Anaerobic digestion （AD） is gaining increasing attention due to the ability to covert organic pollutants into energy-rich biogas and, accordingly, growing interest is paid to the microbial ecology of AD systems. Des...Anaerobic digestion （AD） is gaining increasing attention due to the ability to covert organic pollutants into energy-rich biogas and, accordingly, growing interest is paid to the microbial ecology of AD systems. Despite extensive efforts, AD microbial ecology is still limitedly understood, especially due to the lack of quantitative information on the structures and dynamics of AD microbial communities. Such knowledge gap is particularly pronounced in sewage sludge AD processes although treating sewage sludge is among the major practical applications of AD. Therefore, we examined the microbial communities in three full-scale sewage sludge digesters using qualitative and quantitative molecular techniques in combination： denaturing gradient gel electrophoresis （DGGE） and real-time polymerase chain reaction （PCR）. Eight out of eleven bacterial sequences retrieved from the DGGE analysis were not affiliated to any known species while all eleven archaeal sequences were assigned to known methanogen species. Quantitative real-time PCR analysis revealed that, based on the 16S rRNA gene abundance, the hydrogenotrophic order Methanomicrobiales is the most dominant methanogen group （〉 94% of the total methanogen population） in all digesters. This corresponds well to the prevailing occurrence of the DGGE bands related to Methanolinea and Methanospirillum, both belonging to the order Methanomicrobiales, in all sludge samples. It is therefore suggested that hydrogenotrophic methanogens, especially Methanomicrobiales strains, are likely the major players responsible for biogas production in the digesters studied. Our observation is contrary to the conventional understanding that aceticlastic methanogens generally dominate methanogen communities in stable AD environments, suggesting the need for further studies on the dominance relationship in various AD systems.展开更多
Wetland ecosystems are the most important natural methane(CH_(4))sources,whose fluxes periodically fluctuate.Methanogens(methane producers)and methanotrophs(methane consumers)are considered key factors affecting CH_(4...Wetland ecosystems are the most important natural methane(CH_(4))sources,whose fluxes periodically fluctuate.Methanogens(methane producers)and methanotrophs(methane consumers)are considered key factors affecting CH_(4)fluxes in wetlands.However,the symbiotic relationship between methanogens and methanotrophs remains unclear.To help close this research gap,we collected and analyzed samples from four soil depths in the Dajiuhu subalpine peatland in January,April,July,and October 2019 and acquired seasonal methane flux data from an eddy covariance(EC)system,and investigated relationships.A phylogenetic molecular ecological networks(pMENs)analysis was used to identify keystone species and the seasonal variations of the co-occurrence patterns of methanogenic and methanotrophic communities.The results indicate that the seasonal variations of the interactions between methanogenic and methanotrophic communities contributed to CH_(4)emissions in wetlands.The keystone species discerned by the network analysis also showed their importance in mediating CH_(4)fluxes.Methane(CH_(4))emissions in wetlands were lowest in spring;during this period,the most complex interactions between microbes were observed,with intense competition among methanogens while methanotrophs demonstrated better cooperation.Reverse patterns manifested themselves in summer when the highest CH_(4)flux was observed.Methanoregula formicica was negatively correlated with CH_(4)fluxes and occupied the largest ecological niches in the spring network.In contrast,both Methanocella arvoryzae and Methylocystaceae demonstrated positive correlations with CH_(4)fluxes and were better adapted to the microbial community in the summer.In addition,soil temperature and nitrogen were regarded as significant environmental factors to CH_(4)fluxes.This study was successful in explaining the seasonal patterns and microbial driving mechanisms of CH_(4)emissions in wetlands.展开更多
Background: This study investigated changes in rumen protozoal and methanogenic communities, along with the correlations among microbial taxa and methane(CH_4) production of six Belmont Red Composite beef steers fed t...Background: This study investigated changes in rumen protozoal and methanogenic communities, along with the correlations among microbial taxa and methane(CH_4) production of six Belmont Red Composite beef steers fed tea seed saponins(TSS). Animals were fed in three consecutive feeding periods, a high-grain basal diet for 14 d(BD period) then a period of progressive addition of TSS to the basal diet up to 30 g/d for 20 d(TSS period), followed by the basal diet for 13 d without TSS(BDP post-control period).Results: The study found that TSS supplementation decreased the amount of the protozoal genus Entodinium and increased Polyplastron and Eudiplodinium genera. During BDP period, the protozoa community of steers did not return to the protozoal profiles observed in BD period, with higher proportions of Metadinium and Eudiplodinium and lower Isotricha. The addition of TSS was found to change the structure of methanogen community at the subgenus level by decreasing the abundance of methanogens in the SGMT clade and increasing the abundance of methanogens in the RO clade. The correlation analysis indicated that the abundance of SGMT clade methanogens were positively correlated with Isotricha, and Isotricha genus and SGMT clade methanogens were positively correlated with CH_4 production. While RO clade were positively correlated with the proportion of Metadinium genus, which was negatively correlated with CH_4 emission.Conclusions: These results suggest that different genera of rumen protozoa ciliates appear to be selectively inhibited by TSS, and the change in methanogen community at the subgenus level may be due to the mutualistic relationships between methanogens and rumen ciliates.展开更多
Methanogenic archaea reside primarily in the rumen and the lower segments of the intestines of ruminants, where they utilize the reducing equivalents derived from rumen fermentation to reduce carbon dioxide, formic ac...Methanogenic archaea reside primarily in the rumen and the lower segments of the intestines of ruminants, where they utilize the reducing equivalents derived from rumen fermentation to reduce carbon dioxide, formic acid, or methylamines to methane（CH_4）. Research on methanogens in the rumen has attracted great interest in the last decade because CH_4 emission from ruminants contributes to global greenhouse gas emission and represents a loss of feed energy. Some DNA-based phylogenetic studies have depicted a diverse and dynamic community of methanogens in the rumen. In the past decade, researchers have focused on elucidating the underpinning that determines and affects the diversity, composition, structure, and dynamics of methanogen community of the rumen. Concurrently, many researchers have attempted to develop and evaluate interventions to mitigate enteric CH_4 emission. Although much work has been done using plant secondary metabolites, other approaches such as using nitrate and 3-nitrooxy propanol have also yielded promising results. Most of these antimethanogenic compounds or substances often show inconsistent results among studies and also lead to adverse effects on feed intake and digestion and other aspects of rumen fermentation when fed at doses high enough to achieve effective mitigation. This review provides a brief overview of the rumen methanogens and then an appraisal of most of the antimethanogenic compounds and substances that have been evaluated both in vitro and in vivo. Knowledge gaps and future research needs are also discussed with a focus on methanogens and methane mitigation.展开更多
The β-1,3-glucan from yeast has been extensively examined for its immuno-enhancing effects in animals.However,investigation on the relationship among β-glucan,gut microbiota and immune-modulating effects remains lim...The β-1,3-glucan from yeast has been extensively examined for its immuno-enhancing effects in animals.However,investigation on the relationship among β-glucan,gut microbiota and immune-modulating effects remains limited particularly in pigs.Considering the critical roles of gut methanogens in the microbial fermentation,energy metabolism and disease resistance,we investigated the phylogenetic diversity of methanogens from fermented cultures of porcine colonic digesta with（G） or without（N） yeast β-glucan based on sequences of the archaeal 16S rRNA gene.A total of 145 sequences in the G library were assigned into 8 operational taxonomic units（OTUs） with the majority of sequences（114/145） related to strains Methanobrevibacter millerae or Methanobrevibacter gottschalkii with high identities ranging from 97.9 to 98.6%,followed by 23 sequences to Methanobrevibacter ruminantium,2 sequences to Methanobrevibacter smithii and one sequence to Methanobrevibacter wolinii.The 142 sequences in the N library were assigned to 2 OTUs with most sequences（127/142） related to strains M.millerae or M.gottschalkii with sequence identities ranging from 97.9 to 98.5%,and 15 sequences related to M.gottschalkii with 97.9% identity.Shannon diversity index showed that the G library exhibited significantly higher archaeal diversity（P0.05） and Libshuff analysis indicated the differences in the community structure between the two libraries were significant（P0.0001）.In conclusion,the current study provides evidence that addition of yeast β-glucan significantly increased the diversity of methanogens in in vitro fermented porcine colonic digesta.展开更多
Exploring methane-metabolizing microorganisms'distribution patterns and driving factors is significant for estimating the global methane budget,but our current knowledge is limited.In this study,we took a systemat...Exploring methane-metabolizing microorganisms'distribution patterns and driving factors is significant for estimating the global methane budget,but our current knowledge is limited.In this study,we took a systematic soil and microbial survey along the coast of river channels in the Yellow River Delta,which included the most rapidly deposited sedimentation globally.The prokaryotes,fungi,and protists had more significant changes between two regions with distinct deposition ages than across soil depths,while the accumulation of soil organic matter was the most critical external driving force for the succession of microbial communities.The deposition ages of sedimentary soils also altered the methanogenic and methanotrophic communities,with methanogens showing a greater response to environmental gradient changes than methanotrophs.The distribution of methanogens was mainly influenced by the direct regulation of biological factors represented by fungi and indirectly regulated by environmental stresses along the sedimentation gradient.Our self-developed inter-domain ecological network platform has further investigated the inter-trophic relationships between methane-metabolizing microorganisms and other microbes.Methanogens and methanotrophs form the core species of a highly interconnected network,and there is a strong interdependence between them and fungi and protists,while other prokaryotic species are relatively independent,in addition,methanogens play a central role in species interactions as modular hubs,they tended to be associated with saprotrophic fungi in the older sedimentation region,while in the newer sedimentation region,they were more associated with bacterial groups.This study enhances our understanding of the microbial hierarchical web in coastal wetland ecosystems.展开更多
The information provided by completely sequenced genomes of methanogens can yield insights into a deeper molecular understanding of evolutionary mechanisms.This review describes the advantages of using metabolic pathw...The information provided by completely sequenced genomes of methanogens can yield insights into a deeper molecular understanding of evolutionary mechanisms.This review describes the advantages of using metabolic pathways to clarify evolutionary correlation of methanogens with archaea and prokaryotes.Metabolic trees can be used to highlight similarities in metabolic networks related to the biology of methanogens.Metabolic genes are among the most modular in the cell and their genes are expected to travel laterally,even in recent evolution.Phylogenetic analysis of protein superfamilies provides a perspective on the evolutionary history of some key metabolic modules of methanogens.Phage-related genes from distantly related organisms typically invade methanogens by horizontal gene transfer.Metabolic modules in methanogenesis are phylogenetically aligned in closely related methanogens.Reverse order reactions of methanogenesis are achieved in methylotrophic methanogens using metabolic and structural modules of key enzymes.A significant evolutionary process is thought to couple the utilization of heavy metal ions with energetic metabolism in methanogens.Over 30 of methanogens genomes have been sequenced to date,and a variety of databases are being developed that will provide for genome annotation and phylogenomic analysis of methanogens.Into the context of the evolutionary hypothesis,the integration of metabolomic and proteomic data into large-scale mathematical models holds promise for fostering rational strategies for strain improvement.展开更多
Global efforts to avert climate change cannot succeed without tackling the emission of methane from soil and other ecosystems.Methane is a greenhouse gas that retains heat in the atmosphere and causes global warming.I...Global efforts to avert climate change cannot succeed without tackling the emission of methane from soil and other ecosystems.Methane is a greenhouse gas that retains heat in the atmosphere and causes global warming.Its production is the last step of organic matter decomposition,and it is produced by methanogenic archaea bearing the functional gene mcrA(encoding methyl-coenzyme M reductase).Methane production involves the reduction of acetate or carbon dioxide in a microaerophilic or anaerobic environment under the catalytic actions of methyl-coenzyme M to generate methane.On the other hand,methane-oxidizing bacteria,also known as methanotrophs,through the catalytic action of particulate methane monooxygenase(pMMO),oxidize methane and reduce its emission to the atmosphere.In essence,both production and consumption of methane happen within the soil.Methanotrophs and methanogens inhabit the same soil environment.In fact,a shift in the balance between methanogen and methanotroph activities and abundances could influence soil methane emission and global warming.In this review,we highlight recent advances in drivers of methane flux,pmoA(encoding pMMO)and mcrA gene abundances,methane emission and control,relationships between microbial functional gene abundances and soil functions,and methods for studying the pmoA and mcrA gene abundances in soil.We also highlight gaps that need to be filled and the impact of the mcrA/pmoA gene abundance ratio in driving the methane emission rate in soil.We also discuss the various abiotic factors that control pmoA and mcrA gene abundances.展开更多
Methanogenic archaea are known as human gut inhabitants since more than 30 years ago through the detection of methane in the breath and isolation of two methanogenic species belonging to the order Methanobacteriales, ...Methanogenic archaea are known as human gut inhabitants since more than 30 years ago through the detection of methane in the breath and isolation of two methanogenic species belonging to the order Methanobacteriales, Methanobrevibacter smithii and Methanosphaera stadtmanae. During the last decade, diversity of archaea encountered in the human gastrointestinal tract (GIT) has been extended by sequence identification and culturing of new strains. Here we provide an updated census of the archaeal diversity associated with the human GIT and their possible role in the gut physiology and health. We particularly focus on the still poorly characterized 7<sup>th</sup> order of methanogens, the Methanomassiliicoccales, associated to aged population. While also largely distributed in non-GIT environments, our actual knowledge on this novel order of methanogens has been mainly revealed through GIT inhabitants. They enlarge the number of final electron acceptors of the gut metabolites to mono- di- and trimethylamine. Trimethylamine is exclusively a microbiota-derived product of nutrients (lecithin, choline, TMAO, L-carnitine) from normal diet, from which seems originate two diseases, trimethylaminuria (or Fish-Odor Syndrome) and cardiovascular disease through the proatherogenic property of its oxidized liver-derived form. This therefore supports interest on these methanogenic species and its use as archaebiotics, a term coined from the notion of archaea-derived probiotics.展开更多
Elevated levels of atmospheric CO_(2)(eCO_(2))promote rice growth and increase methane(CH_(4))emissions from rice paddies,because increased input of plant photosynthate to soil stimulates methanogenic archae.However,t...Elevated levels of atmospheric CO_(2)(eCO_(2))promote rice growth and increase methane(CH_(4))emissions from rice paddies,because increased input of plant photosynthate to soil stimulates methanogenic archae.However,temporal trends in the effects of eCO_(2)on rice growth and CH_(4)emissions are still unclear.To investigate changes in the effects of eCO_(2)over time,we conducted a two-season pot experiment in a walk-in growth chamber.Positive effects of eCO_(2)on rice leaf photosynthetic rate,biomass,and grain yield were similar between growing seasons.However,the effects of eCO_(2)on CH_(4) emissions decreased over time.Elevated CO_(2)increased CH_(4)emissions by 48%-101%in the first growing season,but only by 28%-30%in the second growing season.We also identified the microbial process underlying the acclimation of CH4 emissions to atmospheric CO_(2)enrichment:eCO_(2)stimulated the abundance of methanotrophs more strongly in soils that had been previously exposed to eCO_(2)than in soils that had not been.These results emphasize the need for long-term eCO_(2)experiments for accurate predictions of terrestrial feedbacks.展开更多
The microbial community structure and functionally distinct groups in three kinds of produced water samples from the shallow,mesothermic and low-salinity Daqing oil reservoir were systematically evaluated using both c...The microbial community structure and functionally distinct groups in three kinds of produced water samples from the shallow,mesothermic and low-salinity Daqing oil reservoir were systematically evaluated using both culture-dependent and culture-independent methods.Sequence analysis of the 16S rRNA genes indicated that the bacterial library was dominated by Acinetobacter and Arcobacter and the archaeal community was dominated by Methanosaeta and Methanolinea.Two isolated methanogens were closely related with Methanothermobacter thermautotrophicus and Methanoculleus receptaculi.The fermentative bacteria were identified as Pseudomonas,Haloanaerobium,Alcalibacter,Arcobacter,and Pannonibacter.The predominant nitrate-reducing bacteria fell within the genus Pseudomonas.The dominant members of the cultured hydrocarbon-oxidizing bacteria were phylogenetically associated with Micrococcus,Pseudomonas,and Bacillus.Enrichments of biosurfactants and biopolymer producing groups mainly yielded Pseudomonas,Bacillus,and Acenitobacter-related members.The functional groups related to polymer degradation were also affiliated with Pseudomonas and Bacillus.Results from this study provide the fresh insight into the diversity of microbial communities in Daqing petroleum reservoirs.The vast pool of functional strains retrieved in this study was presumed to include the promising strains that could be applied in microbial-enhanced oil recovery in future.展开更多
The characteristics of methane emission were compared among six types of upland and paddy soils developed from different parent materials with distinct physics and chemical properties after planting rice. The fluxes o...The characteristics of methane emission were compared among six types of upland and paddy soils developed from different parent materials with distinct physics and chemical properties after planting rice. The fluxes of methane emission in submerged soils from the upland were obviously lower than those from the paddy rice field. The flux of methane emission in the paddy soil developed from fluvo-aquic soil was the largest among all the types of soils. Planting of rice was helpful to emission of methane in soils. The amounts of various groups of methanogenic flora were conformed with the deferences among the fluxes of methane emission in various types of soils. Methane formation was observed in each type Of air-dried soils stored for a long time after addition of water and incubation at 35℃.展开更多
Microbial electrosynthesis(MES) can potentially provide a mean for storing renewable energy surpluses as chemical energy. However, the fluctuating nature of these energy sources may represent a threat to MES, as the m...Microbial electrosynthesis(MES) can potentially provide a mean for storing renewable energy surpluses as chemical energy. However, the fluctuating nature of these energy sources may represent a threat to MES, as the microbial communities that develop on the biocathode rely on the continuous existence of a polarized electrode. This work assesses how MES performance, product generation and microbial community evolution are affected by a long-period(6 weeks) power off(open circuit). Acetogenic and H2-producing bacteria activity recovered after reconnection. However, few days later syntrophic acetate oxidation bacteria and H2-consuming methanogens became dominant, producing CH4 as the main product, via electromethanogenesis and the syntrophic interaction between eubacterial and archaeal communities which consume both the acetic acid and the hydrogen present in the cathode environment. Thus,the system proved to be resilient to a long-term power interruption in terms of electroactivity. At the same time, these results demonstrated that the system could be extensively affected in both end product generation and microbial communities.展开更多
This letter emphasizes the need to expand discussions on gut microbiome’s role in inflammatory bowel disease(IBD)and colorectal cancer(CRC)by including the often-overlooked non-bacterial components of the human gut f...This letter emphasizes the need to expand discussions on gut microbiome’s role in inflammatory bowel disease(IBD)and colorectal cancer(CRC)by including the often-overlooked non-bacterial components of the human gut flora.It highlights how viral,fungal and archaeal inhabitants of the gut respond towards gut dysbiosis and contribute to disease progression.Viruses such as bacteriophages target certain bacterial species and modulate the immune system.Other viruses found associated include Epstein-Barr virus,human papillomavirus,John Cunningham virus,cytomegalovirus,and human herpes simplex virus type 6.Fungi such as Candida albicans and Malassezia contribute by forming tissue-invasive filaments and producing inflammatory cytokines,respectively.Archaea,mainly methanogens are also found altering the microbial fermentation pathways.This correspondence,thus underscores the significance of considering the pathological and physiological mechanisms of the entire spectrum of the gut microbiota to develop effective therapeutic interventions for both IBD and CRC.展开更多
Background The red macroalgae Asparagopsis is an effective methanogenesis inhibitor due to the presence of halogenated methane(CH_(4))analogues,primarily bromoform(CHBr_(3)).This study aimed to investigate the degrada...Background The red macroalgae Asparagopsis is an effective methanogenesis inhibitor due to the presence of halogenated methane(CH_(4))analogues,primarily bromoform(CHBr_(3)).This study aimed to investigate the degradation process of CHBr3 from A taxiformis in the rumen and whether this process is diet-dependent.An in vitro batch culture system was used according to a 2×2 factorial design,assessing two A taxiformis inclusion rates[0(CTL)and 2%DM diet(AT)]and two diets[high-concentrate(HC)and high-forage diet(HF)].Incubations lasted for 72 h and samples of headspace and fermentation liquid were taken at 0,0.5,1,3,6,8,12,16,24,48 and 72 h to assess the pattern of degradation of CHBr_(3) into dibromomethane(CH_(2)Br_(2))and fermentation parameters.Additionally,an in vitro experiment with pure cultures of seven methanogens strains(Methanobrevibacter smithii,Methanobrevibacter ruminantium,Methanosphaera stadtmanae,Methanosarcina barkeri,Methanobrevibacter millerae,Methanorhermobacter wolfei and Methanobacterium mobile)was conducted to test the effects of increasing concentrations of CHBr3(0.4,2,10and 50μmol/L).Results The addition of AT significantly decreased CH_(4) production(P=0.002)and the acetate:propionate ratio(P=0.003)during a 72-h incubation.The concentrations of CHBr_(3) showed a rapid decrease with nearly 90%degraded within the first 3 h of incubation.On the contrary,CH_(2)Br_(2) concentration quickly increased during the first 6 h and then gradually decreased towards the end of the incubation.Neither CHBr_(3) degradation nor CH_(2)Br_(2) synthesis were affected by the type of diet used as substrate,suggesting that the fermentation rate is not a driving factor involved in CHBr_(3)degradation.The in vitro culture of methanogens showed a dose-response effect of CHBr3 by inhibiting the growth of M.smithii,M.ruminantium,M.stadtmanae,M.barkeri,M.millerae,M.wolfei,and M.mobile.Conclusions The present work demonstrated that CHBr_(3) from A.taxiformis is quickly degraded to CH_(2)Br_(2)in the rumen and that the fermentation rate promoted by different diets is not a driving factor involved in CHBr_(3)degradation.展开更多
Microbial enhanced oil recovery (MEOR) is the research focus in the field of energy development as an environmentally friendly and low cost technology. MEOR can bes divided into indigenous microbial oil recovery and e...Microbial enhanced oil recovery (MEOR) is the research focus in the field of energy development as an environmentally friendly and low cost technology. MEOR can bes divided into indigenous microbial oil recovery and exogenous microbial oil recovery. The ultimate goal of indigenous microbial flooding is to enhance oil recovery via stimulation of specific indigenous microorganisms by injecting optimal nutrients. For studying the specific rule to activate the indigenous community during the long-term injection period, a series of indigenous displacement flooding experiments were carried out by using the long-core physical simulation test. The experimental results have shown that the movement of nutrients components (i.e., carbon/nitrogen/phosphorus) differed from the consumption of them. Moreover, there was a positive relationship between the nutrients concentration and bacteria concentration once observed in the produced fluid. And the trend of concentration of acetic acid was consistent with that of methanogens. When adding same activators, the impacts of selective activators to stimulate the indigenous microorganisms became worse along with the injection period, which led to less oil recovery efficiency.展开更多
The present lab-scale research reveals the enrichment of anaerobic ammonium oxidation microorganism from methanogenic anaerobic granular sludge and the effect of inorganic carbon(sodium bicarbonate)on anaerobic ammoni...The present lab-scale research reveals the enrichment of anaerobic ammonium oxidation microorganism from methanogenic anaerobic granular sludge and the effect of inorganic carbon(sodium bicarbonate)on anaerobic ammonium oxidation.The enrichment of anammox bacteria was carried out in a 7.0-L sequencing batch reactor(SBR)and the effect of bicarbonate on anammox was conducted in a 3.0-L SBR.Research results,especially the biomass,showed first signs of anammox activity after 54 d cultivation with synthetic wastewater,when the pH was controlled between 7.5 and 8.3,the temperature was 35°C.The anammox activity increased as the influent bicarbonate concentration increased from 1.0to 1.5 g/L,and then,was inhibited as the bicarbonate concentration approached 2.0 g/L.However,the activity could be restored by the reduction of bicarbonate concentration to 1.0 g/L,as shown by rapid conversion of ammonium,and nitrite and nitrate production with normal stoichiometry.The optimization of the bicarbonate concentration in the reactor could increase the anammox rate up to 66.4 mgN/(L-d).展开更多
Microbial methanogenesis is a major source of the greenhouse gas methane(CH4).It is the final step in the anaerobic degradation of organic matter when inorganic electron acceptors such as nitrate,ferric iron,or sulfat...Microbial methanogenesis is a major source of the greenhouse gas methane(CH4).It is the final step in the anaerobic degradation of organic matter when inorganic electron acceptors such as nitrate,ferric iron,or sulfate have been depleted.Knowledge of this degradation pathway is important for the creation of mechanistic models,prediction of future CH4 emission scenarios,and development of mitigation strategies.In most anoxic environments,CH4 is produced from either acetate(aceticlastic methanogenesis)or hydrogen(H2)plus carbon dioxide(CO2)(hydrogenotrophic methanogenesis).Hydrogen can be replaced by other CO2-type methanogenesis,using formate,carbon monoxide(CO),or alcohols as substrates.The ratio of these two pathways is tightly constrained by the stoichiometry of conversion processes.If the degradation of organic matter is complete(e.g.,degradation of straw in rice paddies),then fermentation eventually results in production of acetate and H2 at a ratio of>67%aceticlastic and<33%hydrogenotrophic methanogensis.However,acetate production can be favored when heterotrophic or chemolithotrophic acetogenesis is enhanced,and H2 production can be favored when syntrophic acetate oxidation is enhanced.This typically occurs at low and elevated temperatures,respectively.Thus,temperature can strongly influence the methanogenic pathway,which may range from 100%aceticlastic methanogenesis at low temperatures to 100%hydrogenotrophic methanogenesis at high temperatures.However,if the degradation of organic matter is not complete(e.g.,degradation of soil organic matter),the stoichiometry of fermentation is not tightly constrained,resulting,for example,in the preferential production of H2,followed by hydrogenotrophic methanogenesis.Preferential production of CH4 by either aceticlastic or hydrogenotrophic methanogenesis can also happen if one of the methanogenic substrates is not consumed by methanogens but is,instead,accumulated,volatilized,or utilized otherwise.Methylotrophic methanogens,which can use methanol as a substrate,are widespread,but it is unlikely that methanol is produced in similar quantities as acetate,CO2,and H2.Methylotrophic methanogenesis is important in saline environments,where compatible solutes are degraded to methyl compounds(trimethyl amine and dimethyl sulfide)and then serve as non-competitive substrates,while acetate and hydrogen are degraded by non-methanogenic processes,e.g.,sulfate reduction.展开更多
Global warming, as a result of an increase in the mean temperature of the planet, might lead to catastrophic events for humanity. This temperature increase is mainly the result of an increase in the atmospheric greenh...Global warming, as a result of an increase in the mean temperature of the planet, might lead to catastrophic events for humanity. This temperature increase is mainly the result of an increase in the atmospheric greenhouse gases （GHG） concentration. Water vapor, carbon dioxide （CO2）, methane （CH4） and nitrous oxide （N20） are the most important GHG, and human activities, such as industry, livestock and agriculture, contribute to the production of these gases. Methane, at an atmospheric concentration of 1.7 gmol tool-1 currently, is responsible for 16% of the global warming due to its relatively high global warming potential. Soils play an important role in the CH4 cycle as methanotrophy （oxidation of CH4） and methanogenesis （production of CH4） take place in them. Understanding methanogenesis and methanotrophy is essential to establish new agriculture techniques and industrial processes that contribute to a better balance of GHG. The current knowledge of methanogenesis and methanotrophy in soils, anaerobic CH4 oxidation and methanotrophy in extreme environments is also discussed.展开更多
基金supported by the 2013 Research Fund of Ulsan National Institute of Science and Technology through a Future Challenge Project
文摘Anaerobic digestion （AD） is gaining increasing attention due to the ability to covert organic pollutants into energy-rich biogas and, accordingly, growing interest is paid to the microbial ecology of AD systems. Despite extensive efforts, AD microbial ecology is still limitedly understood, especially due to the lack of quantitative information on the structures and dynamics of AD microbial communities. Such knowledge gap is particularly pronounced in sewage sludge AD processes although treating sewage sludge is among the major practical applications of AD. Therefore, we examined the microbial communities in three full-scale sewage sludge digesters using qualitative and quantitative molecular techniques in combination： denaturing gradient gel electrophoresis （DGGE） and real-time polymerase chain reaction （PCR）. Eight out of eleven bacterial sequences retrieved from the DGGE analysis were not affiliated to any known species while all eleven archaeal sequences were assigned to known methanogen species. Quantitative real-time PCR analysis revealed that, based on the 16S rRNA gene abundance, the hydrogenotrophic order Methanomicrobiales is the most dominant methanogen group （〉 94% of the total methanogen population） in all digesters. This corresponds well to the prevailing occurrence of the DGGE bands related to Methanolinea and Methanospirillum, both belonging to the order Methanomicrobiales, in all sludge samples. It is therefore suggested that hydrogenotrophic methanogens, especially Methanomicrobiales strains, are likely the major players responsible for biogas production in the digesters studied. Our observation is contrary to the conventional understanding that aceticlastic methanogens generally dominate methanogen communities in stable AD environments, suggesting the need for further studies on the dominance relationship in various AD systems.
基金supported by the National Science Foundation of China(Grant No.31971490).
文摘Wetland ecosystems are the most important natural methane(CH_(4))sources,whose fluxes periodically fluctuate.Methanogens(methane producers)and methanotrophs(methane consumers)are considered key factors affecting CH_(4)fluxes in wetlands.However,the symbiotic relationship between methanogens and methanotrophs remains unclear.To help close this research gap,we collected and analyzed samples from four soil depths in the Dajiuhu subalpine peatland in January,April,July,and October 2019 and acquired seasonal methane flux data from an eddy covariance(EC)system,and investigated relationships.A phylogenetic molecular ecological networks(pMENs)analysis was used to identify keystone species and the seasonal variations of the co-occurrence patterns of methanogenic and methanotrophic communities.The results indicate that the seasonal variations of the interactions between methanogenic and methanotrophic communities contributed to CH_(4)emissions in wetlands.The keystone species discerned by the network analysis also showed their importance in mediating CH_(4)fluxes.Methane(CH_(4))emissions in wetlands were lowest in spring;during this period,the most complex interactions between microbes were observed,with intense competition among methanogens while methanotrophs demonstrated better cooperation.Reverse patterns manifested themselves in summer when the highest CH_(4)flux was observed.Methanoregula formicica was negatively correlated with CH_(4)fluxes and occupied the largest ecological niches in the spring network.In contrast,both Methanocella arvoryzae and Methylocystaceae demonstrated positive correlations with CH_(4)fluxes and were better adapted to the microbial community in the summer.In addition,soil temperature and nitrogen were regarded as significant environmental factors to CH_(4)fluxes.This study was successful in explaining the seasonal patterns and microbial driving mechanisms of CH_(4)emissions in wetlands.
基金supported by grants from the Natural Science Foundation of China (31272472)project grants from Meat & Livestock Australia,Fisheries and Forestry in Australia and Commonwealth Scientific and Industrial Research Organization (CSIRO)。
文摘Background: This study investigated changes in rumen protozoal and methanogenic communities, along with the correlations among microbial taxa and methane(CH_4) production of six Belmont Red Composite beef steers fed tea seed saponins(TSS). Animals were fed in three consecutive feeding periods, a high-grain basal diet for 14 d(BD period) then a period of progressive addition of TSS to the basal diet up to 30 g/d for 20 d(TSS period), followed by the basal diet for 13 d without TSS(BDP post-control period).Results: The study found that TSS supplementation decreased the amount of the protozoal genus Entodinium and increased Polyplastron and Eudiplodinium genera. During BDP period, the protozoa community of steers did not return to the protozoal profiles observed in BD period, with higher proportions of Metadinium and Eudiplodinium and lower Isotricha. The addition of TSS was found to change the structure of methanogen community at the subgenus level by decreasing the abundance of methanogens in the SGMT clade and increasing the abundance of methanogens in the RO clade. The correlation analysis indicated that the abundance of SGMT clade methanogens were positively correlated with Isotricha, and Isotricha genus and SGMT clade methanogens were positively correlated with CH_4 production. While RO clade were positively correlated with the proportion of Metadinium genus, which was negatively correlated with CH_4 emission.Conclusions: These results suggest that different genera of rumen protozoa ciliates appear to be selectively inhibited by TSS, and the change in methanogen community at the subgenus level may be due to the mutualistic relationships between methanogens and rumen ciliates.
基金supported by funding(award number:2012-67015-19437) from the Agriculture and Food Research Initiative(AFRI) of National Institute of Food and Agriculture(NIFA),US Department of Agriculture
文摘Methanogenic archaea reside primarily in the rumen and the lower segments of the intestines of ruminants, where they utilize the reducing equivalents derived from rumen fermentation to reduce carbon dioxide, formic acid, or methylamines to methane（CH_4）. Research on methanogens in the rumen has attracted great interest in the last decade because CH_4 emission from ruminants contributes to global greenhouse gas emission and represents a loss of feed energy. Some DNA-based phylogenetic studies have depicted a diverse and dynamic community of methanogens in the rumen. In the past decade, researchers have focused on elucidating the underpinning that determines and affects the diversity, composition, structure, and dynamics of methanogen community of the rumen. Concurrently, many researchers have attempted to develop and evaluate interventions to mitigate enteric CH_4 emission. Although much work has been done using plant secondary metabolites, other approaches such as using nitrate and 3-nitrooxy propanol have also yielded promising results. Most of these antimethanogenic compounds or substances often show inconsistent results among studies and also lead to adverse effects on feed intake and digestion and other aspects of rumen fermentation when fed at doses high enough to achieve effective mitigation. This review provides a brief overview of the rumen methanogens and then an appraisal of most of the antimethanogenic compounds and substances that have been evaluated both in vitro and in vivo. Knowledge gaps and future research needs are also discussed with a focus on methanogens and methane mitigation.
基金supported by the Young Scientist Fund of Department of Education of Sichuan Province,China(112A081)
文摘The β-1,3-glucan from yeast has been extensively examined for its immuno-enhancing effects in animals.However,investigation on the relationship among β-glucan,gut microbiota and immune-modulating effects remains limited particularly in pigs.Considering the critical roles of gut methanogens in the microbial fermentation,energy metabolism and disease resistance,we investigated the phylogenetic diversity of methanogens from fermented cultures of porcine colonic digesta with（G） or without（N） yeast β-glucan based on sequences of the archaeal 16S rRNA gene.A total of 145 sequences in the G library were assigned into 8 operational taxonomic units（OTUs） with the majority of sequences（114/145） related to strains Methanobrevibacter millerae or Methanobrevibacter gottschalkii with high identities ranging from 97.9 to 98.6%,followed by 23 sequences to Methanobrevibacter ruminantium,2 sequences to Methanobrevibacter smithii and one sequence to Methanobrevibacter wolinii.The 142 sequences in the N library were assigned to 2 OTUs with most sequences（127/142） related to strains M.millerae or M.gottschalkii with sequence identities ranging from 97.9 to 98.5%,and 15 sequences related to M.gottschalkii with 97.9% identity.Shannon diversity index showed that the G library exhibited significantly higher archaeal diversity（P0.05） and Libshuff analysis indicated the differences in the community structure between the two libraries were significant（P0.0001）.In conclusion,the current study provides evidence that addition of yeast β-glucan significantly increased the diversity of methanogens in in vitro fermented porcine colonic digesta.
基金supported by the National Natural Science Foundation of China(Grant Nos.U1906223,32001092)the Open Project of Key Laboratory of Environmental Biotechnology(Grant No.kf2021003).
文摘Exploring methane-metabolizing microorganisms'distribution patterns and driving factors is significant for estimating the global methane budget,but our current knowledge is limited.In this study,we took a systematic soil and microbial survey along the coast of river channels in the Yellow River Delta,which included the most rapidly deposited sedimentation globally.The prokaryotes,fungi,and protists had more significant changes between two regions with distinct deposition ages than across soil depths,while the accumulation of soil organic matter was the most critical external driving force for the succession of microbial communities.The deposition ages of sedimentary soils also altered the methanogenic and methanotrophic communities,with methanogens showing a greater response to environmental gradient changes than methanotrophs.The distribution of methanogens was mainly influenced by the direct regulation of biological factors represented by fungi and indirectly regulated by environmental stresses along the sedimentation gradient.Our self-developed inter-domain ecological network platform has further investigated the inter-trophic relationships between methane-metabolizing microorganisms and other microbes.Methanogens and methanotrophs form the core species of a highly interconnected network,and there is a strong interdependence between them and fungi and protists,while other prokaryotic species are relatively independent,in addition,methanogens play a central role in species interactions as modular hubs,they tended to be associated with saprotrophic fungi in the older sedimentation region,while in the newer sedimentation region,they were more associated with bacterial groups.This study enhances our understanding of the microbial hierarchical web in coastal wetland ecosystems.
基金the University Grants Commission,New Delhi,India,for financial assistance(32-559/2006)to carry out work described in this review.
文摘The information provided by completely sequenced genomes of methanogens can yield insights into a deeper molecular understanding of evolutionary mechanisms.This review describes the advantages of using metabolic pathways to clarify evolutionary correlation of methanogens with archaea and prokaryotes.Metabolic trees can be used to highlight similarities in metabolic networks related to the biology of methanogens.Metabolic genes are among the most modular in the cell and their genes are expected to travel laterally,even in recent evolution.Phylogenetic analysis of protein superfamilies provides a perspective on the evolutionary history of some key metabolic modules of methanogens.Phage-related genes from distantly related organisms typically invade methanogens by horizontal gene transfer.Metabolic modules in methanogenesis are phylogenetically aligned in closely related methanogens.Reverse order reactions of methanogenesis are achieved in methylotrophic methanogens using metabolic and structural modules of key enzymes.A significant evolutionary process is thought to couple the utilization of heavy metal ions with energetic metabolism in methanogens.Over 30 of methanogens genomes have been sequenced to date,and a variety of databases are being developed that will provide for genome annotation and phylogenomic analysis of methanogens.Into the context of the evolutionary hypothesis,the integration of metabolomic and proteomic data into large-scale mathematical models holds promise for fostering rational strategies for strain improvement.
文摘Global efforts to avert climate change cannot succeed without tackling the emission of methane from soil and other ecosystems.Methane is a greenhouse gas that retains heat in the atmosphere and causes global warming.Its production is the last step of organic matter decomposition,and it is produced by methanogenic archaea bearing the functional gene mcrA(encoding methyl-coenzyme M reductase).Methane production involves the reduction of acetate or carbon dioxide in a microaerophilic or anaerobic environment under the catalytic actions of methyl-coenzyme M to generate methane.On the other hand,methane-oxidizing bacteria,also known as methanotrophs,through the catalytic action of particulate methane monooxygenase(pMMO),oxidize methane and reduce its emission to the atmosphere.In essence,both production and consumption of methane happen within the soil.Methanotrophs and methanogens inhabit the same soil environment.In fact,a shift in the balance between methanogen and methanotroph activities and abundances could influence soil methane emission and global warming.In this review,we highlight recent advances in drivers of methane flux,pmoA(encoding pMMO)and mcrA gene abundances,methane emission and control,relationships between microbial functional gene abundances and soil functions,and methods for studying the pmoA and mcrA gene abundances in soil.We also highlight gaps that need to be filled and the impact of the mcrA/pmoA gene abundance ratio in driving the methane emission rate in soil.We also discuss the various abiotic factors that control pmoA and mcrA gene abundances.
基金Supported by Ph D Scholarship from the French"Ministère de l’Enseignement Supérieur et de la Recherche"(To Nadia Gaci)Science Foundation Ireland through a postdoctoral grant of the Alimentary Pharmabiotic Centre(to Guillaume Borrel)+2 种基金Ph D Scholarship of the European Union(UE)and the Auvergne Council(FEDER)(to William Tottey)Science Foundation Ireland through a Principal Investigator awardby an FHRI award to the ELDERMET project by the Department Agriculture,Fisheries and Marine of the Government of Ireland(to Paul W O’Toole)
文摘Methanogenic archaea are known as human gut inhabitants since more than 30 years ago through the detection of methane in the breath and isolation of two methanogenic species belonging to the order Methanobacteriales, Methanobrevibacter smithii and Methanosphaera stadtmanae. During the last decade, diversity of archaea encountered in the human gastrointestinal tract (GIT) has been extended by sequence identification and culturing of new strains. Here we provide an updated census of the archaeal diversity associated with the human GIT and their possible role in the gut physiology and health. We particularly focus on the still poorly characterized 7<sup>th</sup> order of methanogens, the Methanomassiliicoccales, associated to aged population. While also largely distributed in non-GIT environments, our actual knowledge on this novel order of methanogens has been mainly revealed through GIT inhabitants. They enlarge the number of final electron acceptors of the gut metabolites to mono- di- and trimethylamine. Trimethylamine is exclusively a microbiota-derived product of nutrients (lecithin, choline, TMAO, L-carnitine) from normal diet, from which seems originate two diseases, trimethylaminuria (or Fish-Odor Syndrome) and cardiovascular disease through the proatherogenic property of its oxidized liver-derived form. This therefore supports interest on these methanogenic species and its use as archaebiotics, a term coined from the notion of archaea-derived probiotics.
基金supported by the National Key Research and Development Program of China(2017YFD0300104,2016YFD0300903,2015BAC02B02)the National Natural Science Foundation of China(32022061)+3 种基金the Special Fund for Agroscientific Research in the Public Interest(201503118,201503122)the Agricultural Science and Technology Innovation Program of CAAS(Y2016PT12,Y2016XT01)the Modern Agricultural Development of Jiangsu Province(2019-SJ-039-07)the GEF Project of Climate Smart Staple Crop Production in China(P144531)。
文摘Elevated levels of atmospheric CO_(2)(eCO_(2))promote rice growth and increase methane(CH_(4))emissions from rice paddies,because increased input of plant photosynthate to soil stimulates methanogenic archae.However,temporal trends in the effects of eCO_(2)on rice growth and CH_(4)emissions are still unclear.To investigate changes in the effects of eCO_(2)over time,we conducted a two-season pot experiment in a walk-in growth chamber.Positive effects of eCO_(2)on rice leaf photosynthetic rate,biomass,and grain yield were similar between growing seasons.However,the effects of eCO_(2)on CH_(4) emissions decreased over time.Elevated CO_(2)increased CH_(4)emissions by 48%-101%in the first growing season,but only by 28%-30%in the second growing season.We also identified the microbial process underlying the acclimation of CH4 emissions to atmospheric CO_(2)enrichment:eCO_(2)stimulated the abundance of methanotrophs more strongly in soils that had been previously exposed to eCO_(2)than in soils that had not been.These results emphasize the need for long-term eCO_(2)experiments for accurate predictions of terrestrial feedbacks.
基金supported by Chinese Academy of Science through the Knowledge Innovation Project of The Chinese Academy of Sciences (06LYQY3001)Funding for this project was also provided by Daqing Oilfield Co. Ltd., China
文摘The microbial community structure and functionally distinct groups in three kinds of produced water samples from the shallow,mesothermic and low-salinity Daqing oil reservoir were systematically evaluated using both culture-dependent and culture-independent methods.Sequence analysis of the 16S rRNA genes indicated that the bacterial library was dominated by Acinetobacter and Arcobacter and the archaeal community was dominated by Methanosaeta and Methanolinea.Two isolated methanogens were closely related with Methanothermobacter thermautotrophicus and Methanoculleus receptaculi.The fermentative bacteria were identified as Pseudomonas,Haloanaerobium,Alcalibacter,Arcobacter,and Pannonibacter.The predominant nitrate-reducing bacteria fell within the genus Pseudomonas.The dominant members of the cultured hydrocarbon-oxidizing bacteria were phylogenetically associated with Micrococcus,Pseudomonas,and Bacillus.Enrichments of biosurfactants and biopolymer producing groups mainly yielded Pseudomonas,Bacillus,and Acenitobacter-related members.The functional groups related to polymer degradation were also affiliated with Pseudomonas and Bacillus.Results from this study provide the fresh insight into the diversity of microbial communities in Daqing petroleum reservoirs.The vast pool of functional strains retrieved in this study was presumed to include the promising strains that could be applied in microbial-enhanced oil recovery in future.
文摘The characteristics of methane emission were compared among six types of upland and paddy soils developed from different parent materials with distinct physics and chemical properties after planting rice. The fluxes of methane emission in submerged soils from the upland were obviously lower than those from the paddy rice field. The flux of methane emission in the paddy soil developed from fluvo-aquic soil was the largest among all the types of soils. Planting of rice was helpful to emission of methane in soils. The amounts of various groups of methanogenic flora were conformed with the deferences among the fluxes of methane emission in various types of soils. Methane formation was observed in each type Of air-dried soils stored for a long time after addition of water and incubation at 35℃.
基金the Spanish“Ministerio de Educación,Cultura y Deporte”for the predoctoral FPU Grant(FPU14/01573)the‘Ministerio de Economía y Competitividad’for the support of project ref:CTQ2015-68925-R(MINECO/FEDER,EU)。
文摘Microbial electrosynthesis(MES) can potentially provide a mean for storing renewable energy surpluses as chemical energy. However, the fluctuating nature of these energy sources may represent a threat to MES, as the microbial communities that develop on the biocathode rely on the continuous existence of a polarized electrode. This work assesses how MES performance, product generation and microbial community evolution are affected by a long-period(6 weeks) power off(open circuit). Acetogenic and H2-producing bacteria activity recovered after reconnection. However, few days later syntrophic acetate oxidation bacteria and H2-consuming methanogens became dominant, producing CH4 as the main product, via electromethanogenesis and the syntrophic interaction between eubacterial and archaeal communities which consume both the acetic acid and the hydrogen present in the cathode environment. Thus,the system proved to be resilient to a long-term power interruption in terms of electroactivity. At the same time, these results demonstrated that the system could be extensively affected in both end product generation and microbial communities.
文摘This letter emphasizes the need to expand discussions on gut microbiome’s role in inflammatory bowel disease(IBD)and colorectal cancer(CRC)by including the often-overlooked non-bacterial components of the human gut flora.It highlights how viral,fungal and archaeal inhabitants of the gut respond towards gut dysbiosis and contribute to disease progression.Viruses such as bacteriophages target certain bacterial species and modulate the immune system.Other viruses found associated include Epstein-Barr virus,human papillomavirus,John Cunningham virus,cytomegalovirus,and human herpes simplex virus type 6.Fungi such as Candida albicans and Malassezia contribute by forming tissue-invasive filaments and producing inflammatory cytokines,respectively.Archaea,mainly methanogens are also found altering the microbial fermentation pathways.This correspondence,thus underscores the significance of considering the pathological and physiological mechanisms of the entire spectrum of the gut microbiota to develop effective therapeutic interventions for both IBD and CRC.
基金funded by Blue Ocean Barns.AB has a Ramón y Cajal research contract(RYC2019-027764-I)funded by the Spanish State Research Agency(AEI)。
文摘Background The red macroalgae Asparagopsis is an effective methanogenesis inhibitor due to the presence of halogenated methane(CH_(4))analogues,primarily bromoform(CHBr_(3)).This study aimed to investigate the degradation process of CHBr3 from A taxiformis in the rumen and whether this process is diet-dependent.An in vitro batch culture system was used according to a 2×2 factorial design,assessing two A taxiformis inclusion rates[0(CTL)and 2%DM diet(AT)]and two diets[high-concentrate(HC)and high-forage diet(HF)].Incubations lasted for 72 h and samples of headspace and fermentation liquid were taken at 0,0.5,1,3,6,8,12,16,24,48 and 72 h to assess the pattern of degradation of CHBr_(3) into dibromomethane(CH_(2)Br_(2))and fermentation parameters.Additionally,an in vitro experiment with pure cultures of seven methanogens strains(Methanobrevibacter smithii,Methanobrevibacter ruminantium,Methanosphaera stadtmanae,Methanosarcina barkeri,Methanobrevibacter millerae,Methanorhermobacter wolfei and Methanobacterium mobile)was conducted to test the effects of increasing concentrations of CHBr3(0.4,2,10and 50μmol/L).Results The addition of AT significantly decreased CH_(4) production(P=0.002)and the acetate:propionate ratio(P=0.003)during a 72-h incubation.The concentrations of CHBr_(3) showed a rapid decrease with nearly 90%degraded within the first 3 h of incubation.On the contrary,CH_(2)Br_(2) concentration quickly increased during the first 6 h and then gradually decreased towards the end of the incubation.Neither CHBr_(3) degradation nor CH_(2)Br_(2) synthesis were affected by the type of diet used as substrate,suggesting that the fermentation rate is not a driving factor involved in CHBr_(3)degradation.The in vitro culture of methanogens showed a dose-response effect of CHBr3 by inhibiting the growth of M.smithii,M.ruminantium,M.stadtmanae,M.barkeri,M.millerae,M.wolfei,and M.mobile.Conclusions The present work demonstrated that CHBr_(3) from A.taxiformis is quickly degraded to CH_(2)Br_(2)in the rumen and that the fermentation rate promoted by different diets is not a driving factor involved in CHBr_(3)degradation.
文摘Microbial enhanced oil recovery (MEOR) is the research focus in the field of energy development as an environmentally friendly and low cost technology. MEOR can bes divided into indigenous microbial oil recovery and exogenous microbial oil recovery. The ultimate goal of indigenous microbial flooding is to enhance oil recovery via stimulation of specific indigenous microorganisms by injecting optimal nutrients. For studying the specific rule to activate the indigenous community during the long-term injection period, a series of indigenous displacement flooding experiments were carried out by using the long-core physical simulation test. The experimental results have shown that the movement of nutrients components (i.e., carbon/nitrogen/phosphorus) differed from the consumption of them. Moreover, there was a positive relationship between the nutrients concentration and bacteria concentration once observed in the produced fluid. And the trend of concentration of acetic acid was consistent with that of methanogens. When adding same activators, the impacts of selective activators to stimulate the indigenous microorganisms became worse along with the injection period, which led to less oil recovery efficiency.
文摘The present lab-scale research reveals the enrichment of anaerobic ammonium oxidation microorganism from methanogenic anaerobic granular sludge and the effect of inorganic carbon(sodium bicarbonate)on anaerobic ammonium oxidation.The enrichment of anammox bacteria was carried out in a 7.0-L sequencing batch reactor(SBR)and the effect of bicarbonate on anammox was conducted in a 3.0-L SBR.Research results,especially the biomass,showed first signs of anammox activity after 54 d cultivation with synthetic wastewater,when the pH was controlled between 7.5 and 8.3,the temperature was 35°C.The anammox activity increased as the influent bicarbonate concentration increased from 1.0to 1.5 g/L,and then,was inhibited as the bicarbonate concentration approached 2.0 g/L.However,the activity could be restored by the reduction of bicarbonate concentration to 1.0 g/L,as shown by rapid conversion of ammonium,and nitrite and nitrate production with normal stoichiometry.The optimization of the bicarbonate concentration in the reactor could increase the anammox rate up to 66.4 mgN/(L-d).
基金the Fonds der Chemischen Industrie (Fonds of the Chemical Industry), Germany.
文摘Microbial methanogenesis is a major source of the greenhouse gas methane(CH4).It is the final step in the anaerobic degradation of organic matter when inorganic electron acceptors such as nitrate,ferric iron,or sulfate have been depleted.Knowledge of this degradation pathway is important for the creation of mechanistic models,prediction of future CH4 emission scenarios,and development of mitigation strategies.In most anoxic environments,CH4 is produced from either acetate(aceticlastic methanogenesis)or hydrogen(H2)plus carbon dioxide(CO2)(hydrogenotrophic methanogenesis).Hydrogen can be replaced by other CO2-type methanogenesis,using formate,carbon monoxide(CO),or alcohols as substrates.The ratio of these two pathways is tightly constrained by the stoichiometry of conversion processes.If the degradation of organic matter is complete(e.g.,degradation of straw in rice paddies),then fermentation eventually results in production of acetate and H2 at a ratio of>67%aceticlastic and<33%hydrogenotrophic methanogensis.However,acetate production can be favored when heterotrophic or chemolithotrophic acetogenesis is enhanced,and H2 production can be favored when syntrophic acetate oxidation is enhanced.This typically occurs at low and elevated temperatures,respectively.Thus,temperature can strongly influence the methanogenic pathway,which may range from 100%aceticlastic methanogenesis at low temperatures to 100%hydrogenotrophic methanogenesis at high temperatures.However,if the degradation of organic matter is not complete(e.g.,degradation of soil organic matter),the stoichiometry of fermentation is not tightly constrained,resulting,for example,in the preferential production of H2,followed by hydrogenotrophic methanogenesis.Preferential production of CH4 by either aceticlastic or hydrogenotrophic methanogenesis can also happen if one of the methanogenic substrates is not consumed by methanogens but is,instead,accumulated,volatilized,or utilized otherwise.Methylotrophic methanogens,which can use methanol as a substrate,are widespread,but it is unlikely that methanol is produced in similar quantities as acetate,CO2,and H2.Methylotrophic methanogenesis is important in saline environments,where compatible solutes are degraded to methyl compounds(trimethyl amine and dimethyl sulfide)and then serve as non-competitive substrates,while acetate and hydrogen are degraded by non-methanogenic processes,e.g.,sulfate reduction.
基金Supported by the Centro de Investigación y de Estudios Avanzados del IPN,Mexico and the Consejo Nacional de Ciencia y Tecnología,Mexico(Nos.153216,232468 and 245119)
文摘Global warming, as a result of an increase in the mean temperature of the planet, might lead to catastrophic events for humanity. This temperature increase is mainly the result of an increase in the atmospheric greenhouse gases （GHG） concentration. Water vapor, carbon dioxide （CO2）, methane （CH4） and nitrous oxide （N20） are the most important GHG, and human activities, such as industry, livestock and agriculture, contribute to the production of these gases. Methane, at an atmospheric concentration of 1.7 gmol tool-1 currently, is responsible for 16% of the global warming due to its relatively high global warming potential. Soils play an important role in the CH4 cycle as methanotrophy （oxidation of CH4） and methanogenesis （production of CH4） take place in them. Understanding methanogenesis and methanotrophy is essential to establish new agriculture techniques and industrial processes that contribute to a better balance of GHG. The current knowledge of methanogenesis and methanotrophy in soils, anaerobic CH4 oxidation and methanotrophy in extreme environments is also discussed.
