The environmental problems caused by plastics of fossil origin are well known. To reduce harmful impact on the environment, bacterial-based plastics, such as polyhydroxyalkanoates (PHAs), are a promising solution. Mic...The environmental problems caused by plastics of fossil origin are well known. To reduce harmful impact on the environment, bacterial-based plastics, such as polyhydroxyalkanoates (PHAs), are a promising solution. Microbial PHAs can be produced using abundant and inexpensive agricultural by-products as raw material. In this study, the potential use of Cupriavidus necator 11599 for the bioconversion of cassava starch into biodegradable PHAs was explored. Although Cupriavidus necator 11599 is a well-known PHA producer, it cannot grow directly on starch. Thus, acid hydrolysis was carried out on the starch extracted from cassava peels to obtain fermentable sugars. Optimal concentration of reducing sugars (RSs) was obtained by hydrolysis of cassava peel starch with sulfuric acid concentrations of 0.4 N and 0.6 N, at 95˚C and 4 h. The hydrolyzed starch was used for PHA production in Erlenmeyer flasks using reducing sugars (RSs) concentrations ranging from 10 g/L to 25 g/L. The best RS concentration 20 g/L and 25 g/L gave 85.13% ± 1.17% and 89.01% ± 2.49% of biomass PHA content and biomass concentrations of 8.18 g/L and 8.32 g/L, respectively in 48 hours. This research demonstrates that cassava peel starch as an inexpensive feedstock could be used for PHA production, paving the way for the use of other starchy materials to make bioplastics.展开更多
Microbial polyhydroxyalkanoates （PHAs） are a family of biopolyesters produced by many wild type and engineered bacteria. PHAs have diverse structures accompanied by flexible thermal and mechanical properties. Combin...Microbial polyhydroxyalkanoates （PHAs） are a family of biopolyesters produced by many wild type and engineered bacteria. PHAs have diverse structures accompanied by flexible thermal and mechanical properties. Combined with their in vitro biodegradation, cell and tissue compatibility, PHAs have been studied for medical applications, especially medical implants applications, including heart valve tissue engineering, vascular tissue engineering, bone tissue engineering, cartilage tissue engineering, nerve conduit tissue engineering as well as esophagus tissue engineering. Most studies have been conducted in the authors＇ lab in the past 20＋ years. Recently, mechanism on PHA promoted tissue regeneration was revealed to relate to cell responses to PHA biodegradation products and cell-material interactions mediated by microRNA. Very importantly, PHA implants were found not to cause carcinogenesis during long-term implantation. Thus, PHAs should have a bright future in biomedical areas.展开更多
Many bacteria have been found to synthesize a family of polyesters termed polyhydroxyalkanoate, abbreviated as PHA. Some interesting physical properties of PHAs such as piezoelectricity, non-linear optical activity, b...Many bacteria have been found to synthesize a family of polyesters termed polyhydroxyalkanoate, abbreviated as PHA. Some interesting physical properties of PHAs such as piezoelectricity, non-linear optical activity, biocompatibility and biodegradability offer promising applications in areas such as degradable packaging, tissue engineering and drug delivery. Over 90 PHAs with various structure variations have been reported and the number is still increasing. The mechanical property of PHAs changes from brittle to flexible to elastic, depending on the side-chainlength of PHA. Many attempts have been made to produce PHAs as biodegradable plastics using various microorganisms obtained from screening natural environments, genetic engineering and mutation. Due to the high production cost, PHAs still can not compete with the nondegradable plastics, such as polyethylene and polypropylene. Various processes have been developed using low cost raw materials for fermentation and an inorganic extraction process for PHA purification. However, a super PHA production strain may play the most critical role for any large-scale PHA production. Our recent study showed that PHA synthesis is a common phenomenon among bacteria inhabiting various locations, especially oil-contaminated soils. This is very important for finding a suitable bacterial strain for PHA production. In fact, PHA production strains capable of rapid growth and rapid PHA synthesis on cheap molasses substrate have been found on molasses contaminated soils. A combination of novel properties and lower cost will allow easier commercialization of PHA for many applications.展开更多
The production of polyhydroxyalkanoates(PHA) from wastewaters using microbial mixed cultures(MMC) has been attracting increased interest because of PHA's biodegradability characteristics. Production of PHA by an M...The production of polyhydroxyalkanoates(PHA) from wastewaters using microbial mixed cultures(MMC) has been attracting increased interest because of PHA's biodegradability characteristics. Production of PHA by an MMC enriched with PHA-accumulating bacteria was compared using anaerobically treated and acidified brewery wastewaters under various feeding strategies, namely pulse and batch feed addition. To obtain an enriched MMC, a sequencing batch reactor was inoculated with activated sludge fed with acetate and subjected to aerobic dynamic feeding. The enriched MMC was able to accumulate PHA up to 72.6% of cell dry weight(CDW) with pulse addition of acetate controlled by the dissolved oxygen(DO) concentration in the reactor. In a batch accumulation experiment with acetate,the PHA content achieved(28.5% CDW) was less than that of the pulse feeding strategy with the same amount of acetate(～2000 mg C/L). Using anaerobically treated and acidified brewery wastewater fed in pulses, the maximum PHA accumulated by the enriched MMC was similar for both wastewaters(45% CDW), in spite of the higher volatile fatty acid concentration in acidified brewery wastewater. The pulse feed addition controlled by the DO concentration was difficult to implement for wastewater as compared to acetate because the difference in DO concentration between substrate availability and depletion was low. For the batch addition of acidified wastewater, a slightly lower PHA content(39%CDW) was obtained. These results show that both brewery wastewaters can be utilized for PHA production with a similar maximum PHA storage capacity.展开更多
Four sequence batch reactors（SBRs） fed by fermented sugar cane wastewater were continuously operated under the aerobic dynamic feeding（ADF） mode with different configurations of sludge retention time（SRT）, carbo...Four sequence batch reactors（SBRs） fed by fermented sugar cane wastewater were continuously operated under the aerobic dynamic feeding（ADF） mode with different configurations of sludge retention time（SRT）, carbon and initial biomass concentrations to enrich polyhydroxyalkanoate（PHA） accumulating mixed microbial cultures（MMCs） from municipal activated sludge.The stability of SBRs was investigated besides the enrichment performance. The microbial community structures of the enriched MMCs were analyzed using terminal restriction fragment length polymorphism（T-RFLP）. The optimum operating conditions for the enrichment process were： SRT of 5 days, carbon concentration of 2.52 g COD/L and initial biomass concentration of3.65 g/L. The best enrichment performance in terms of both operating stability and PHA storage ability of enriched cultures（with the maximum PHA content and PHA storage yield（YPHA/S） of61.26% and 0.68 mg COD/mg COD, respectively） was achieved under this condition. Effects of the SRT, carbon concentration and initial biomass concentration on the PHA accumulating MMCs selection process were discussed respectively. A new model including the segmentation of the enrichment process and the effects of SRT on each phase was proposed.展开更多
In this work, sucrose utilizing microbes from soil were screened to evaluate their ability for accumulation of biopolymer of polyhydroxyalkanoate （PHA）. Among 72 isolates were transferred to mineral salt medium （MS...In this work, sucrose utilizing microbes from soil were screened to evaluate their ability for accumulation of biopolymer of polyhydroxyalkanoate （PHA）. Among 72 isolates were transferred to mineral salt medium （MSM）, 33 strains can be grown on sucrose agar medium. However, only one strain showed a strong black color for Sudan Black and gave positive result for Nile blue A. Identification by 16S rDNA nucleotide sequence homology of the isolate showed very closely to Hydrogenophaga sp. （99% identify）. To consider PHA production, the isolate was grown in the medium containing sucrose as a sole carbon under controlled conditions of 35 ℃ and at pH 7. Maximum dry cell weight （DCW） and PHA production were obtained at 3.61 g/L and 2.41 g/L after 36 and 42 h batch fermentation. Sucrose uptake measured in term of total organic carbon （TOC） showed at 14.73 g within 48 h. The highest PHA was 68.15% （gPHA/gDCW） giving maximum PHA yield （YP/s） of 0.17 （gPHA/gs ） and a productivity of 0.057 gPHA/L.h. This highlights the potential of microbial resources in soil environment and may be an exploitable application for the industrial production of PHA.展开更多
Concerns about feasibility,separability,settleability,efficiency once hampered studies on polyhydroxyalkanoates(PHAs)production,which mainly focused on single strain microorganism or activated sludge rather than artif...Concerns about feasibility,separability,settleability,efficiency once hampered studies on polyhydroxyalkanoates(PHAs)production,which mainly focused on single strain microorganism or activated sludge rather than artificial microbial consortia.Here,a medium chain length PHAs(mcl-PHAs)producing Pseudomonas-Saccharomyces consortium with xylose as the main substrate was studied.Mcl-PHAs accumulation increased from 12.69 mg·L^-1 to 152.3 mg·L^-1 without any optimization method.The presence of Saccharomyces cerevisiae,though in a relatively low concentration,improved the sedimentation of cell mass of the mixed culture by 60%.Reasons for better sedimentation of the consortium were complex:first,the length of Pseudomonas putida increased two to three times in the consortium;second,the positive surface charge of P.putida was neutralized by S.cerevisiae;third,the adhesion proteins on the surface of S.cerevisiae interacted with the P.putida.展开更多
A total of 5 biochemically characterized lipase positive bacterial strains were screened for Polyhydroxyalkanoates(PHA)production by Nile blue staining and confirmation was done by Sudan Black B.PHA production ability...A total of 5 biochemically characterized lipase positive bacterial strains were screened for Polyhydroxyalkanoates(PHA)production by Nile blue staining and confirmation was done by Sudan Black B.PHA production ability for all strains was optimized followed by time profiling calculation and comparison via using glucose and two plant oils i.e.,canola and mustard oil.Quantitative analysis showed that glucose can serve as a carbon source for maximum biomass(2.5 g/L CDW for strain 5)and PHA production(70.3%for strain 2).PHA produced by strain 2 was further analyzed for its chemical composition and type via Fourier Transform Infrared(FT-IR)spectroscopy.It revealed homopolymer(PHB)and copolymer(PHB-co-PHV)production of PHA(peaks at 1743 cm-1 and 2861 cm-1,respectively)with both canola and mustard oil unlike glucose which produced only homopolymer one i.e.,PHB(peaks at 1110 cm-1,1411 cm-1 and 1650 cm-1).Crystallinity of FT-IR analyzed PHA was calculated using mathematical formulas which showed decrease from glucose to canola to mustard oil.This study revealed that plant oils can serve as better carbon source to produce better quality(ductile and copolymer)PHA.Moreover,16S rRNA gene sequencing analysis showed that strain 1,strain 2,strain 3,strain 4 and strain 5 are Stenotrophomonas sp.N3,Exiguobacterium sp.N4,Exiguobacterium sp.Ch3,Cellulosimicrobium sp.A8 and Klebsiella sp.LFSM2,respectively.展开更多
Polyhydroxyalkanoates （PHAs）, as a candidate for biodegradable plastic materials, can be synthesized by numerous microorganisms. However, as its production cost is high in comparison with those of chemically synthes...Polyhydroxyalkanoates （PHAs）, as a candidate for biodegradable plastic materials, can be synthesized by numerous microorganisms. However, as its production cost is high in comparison with those of chemically synthesized plastics, a lot of research has been focused on the efficient production of PHAs using different methods. In the present study, the mutation effects of PHAs production in strain pCB4 were investigated with implantation of low energy ions. It was found that under the implantation conditions of 7.8×10^14 N^＋/cm^2 at 10 keV, a high-yield PHAs strain with high genetic stability was generated from many mutants. After optimizing its fermentation conditions, the biomass, PHAs concentration and PHAs content of pCBH4 reached 2.26 g/L, 1.81 g/L, and 80.08% respectively, whereas its wild type controls were about 1.24 g/L, 0.61 g/L, and 49.20%. Moreover, the main constituent of PHAs was identified as poly-3-hydroxybutyrates （PHB） in the mutant stain and the yield of this compound was increased up to 41.33% in contrast to that of 27.78% in the wild type strain.展开更多
Gas chromatography determination of polyhydroxyalkanoates has been common;however,the pretreatment steps are often complex,and gas chromatography operation conditions are not given in detail.In this study,gas chromato...Gas chromatography determination of polyhydroxyalkanoates has been common;however,the pretreatment steps are often complex,and gas chromatography operation conditions are not given in detail.In this study,gas chromatography is used for analyzing PHB,PHV and PH2MV,three majors of PHAs in activated sludge.The sample was centrifuged at a speed of 4000 r/min for the separation of floc and supernatant,freezen,and dried for 12 h in vacuum freezing drier;and then transferred to the fridge for freezing to ice and drying for 12 h in vacuum freezing drier;then chloroform and a simple composition digestion solution including methanol,sulfuric acid and benzoic acid was added;digested at 105 ℃ for 6 h;cooled to room temperature,the lower solution of the result can be used for analyzing.Samples were analyzed by gas chromatography with FID detector and auto sampler;the standard curve of standard material shows an excellent linear relationship with correlation coefficients larger than 0.99;the relative standard deviation (RSD) of sludge samples is less than 1%.The recovery rates of each sample are between 95%-105%.The GC analysis time of each PHA sample is shorter than 10 minutes.展开更多
Polyhydroxyalkanoates（PHAs）were synthesized in activated sludge using three types of carbon sources（sodium acetate,sodium propionate and sodium butyrate）,and their characterization were studied.It was shown that t...Polyhydroxyalkanoates（PHAs）were synthesized in activated sludge using three types of carbon sources（sodium acetate,sodium propionate and sodium butyrate）,and their characterization were studied.It was shown that the content of PHA synthesized by microorganisms in activated sludge were different.The biggest synthetic amount up to 36.7% of VSS was obtained when sodium acetate was used as carbon source.The polymer yield was lower when using sodium propionate as the carbon source than when using others,with25.1% of VSS,while resulted in an increase of hydroxyvalerate（HV）units produced.The structure and thermal properties of extracted biopolymers were analyzed by scanning electron microscope（SEM）,Fourier transform infrared spectroscopy（FTIR）and themogravimetry（TG）.展开更多
Pseudomonas putida KT217 was grown on a complex medium comprised of co-products of the ethanol and biodiesel industries to assess the organism's capability to produce medium-chain-length polyhydroxyalkanoate (mcl-...Pseudomonas putida KT217 was grown on a complex medium comprised of co-products of the ethanol and biodiesel industries to assess the organism's capability to produce medium-chain-length polyhydroxyalkanoate (mcl-PHA). The growth phase was carried out in a medium containing 400 g/L condensed corn solubles (CCS), supplemented with ammonium hydroxide as a nitrogen source. Following the exponential phase, co-products of the biodiesel industry (soapstock and glycerin) were fed into the reactor to trigger PHA production. When glycerin was added to the bioreactor (75 g/L total addition), the final cell dry weight (CDW) and PHA content were 30 g/L and 31%, respectively. The monomeric composition in the PHA formed was relatively uniform throughout incubation with 3-hydroxydecanoate dominating. When a total of 153 g/L of sunflower soapstock was added to the bioreactor in a fed-batch manner, the final CDW and PHA content were 17 g/L and 17%, respectively. Following addition of soapstock the monomeric composition of the polymer changed dramatically, with the 3-hydroxyoctanoate monomer becoming dominant and greater unsaturation present in the PHA.展开更多
Thick cathodes can overcome the low capacity issues,which mostly hamper the performance of the conventional active cathode materials,used in rechargeable Li batteries.However,the typical slurry-based method induces cr...Thick cathodes can overcome the low capacity issues,which mostly hamper the performance of the conventional active cathode materials,used in rechargeable Li batteries.However,the typical slurry-based method induces cracking and flaking during the fabrication of thick electrodes.In addition,a significant increase in the charge-transfer resistance and local cur-rent overload results in poor rate capabilities and cycling stabilities,thereby limiting electrode thickening.In this study,a synergistic dual-network combination strategy based on a conductive nanofibrillar network(CNN)and a nano-bridging amor-phous polyhydroxyalkanoate(aPHA)binder is used to demonstrate the feasibility of constructing a high-performance thick cathode.The CNN and aPHA dual network facilitates the fabrication of a thick cathode(≥250μm thickness and≥90 wt%active cathode material)by a mass-producible slurry method.The thick cathode exhibited a high rate capability and excel-lent cycling stability.In addition,the thick cathode and thin Li metal anode pair(Li//t-NCM)exhibited an optimal energy performance,affording high-performance Li metal batteries with a high areal energy of~25.3 mW h cm^(-2),a high volumetric power density of~1720 W L^(-1),and an outstanding specific energy of~470 W h kg^(-1)at only 6 mA h cm^(-2).展开更多
Poly(3-hydroxybutyrate),a crucial member of the large biodegradable polyhydroxyalkanoate family,suffers from its brittleness.To enhance its performance,we employed a straightforward approach involving the ring-opening...Poly(3-hydroxybutyrate),a crucial member of the large biodegradable polyhydroxyalkanoate family,suffers from its brittleness.To enhance its performance,we employed a straightforward approach involving the ring-opening copolymerization of racemic-β-butyrolactone(rac-β-BL)andβ-propiolactone(β-PL)using the syndio-selective amino-alkoxy-bis(phenolate)-yttrium complex as a catalyst,thanks to the excellent ductility of poly(3-hydroxypropionate).Control over the rac-β-BL/β-PL feeding ratios and polymerization time yielded random or block copolymers with tunable thermal and mechanical properties comparable to traditional fossil-based plastics.Furthermore,we achieved one-pot synthesis of hard-soft-hard triblock copolymers by exploiting monomers’different copolymerization rates and a bifunctional initiator,thus transforming polyhydroxyalkanoates from hard and tough plastics to soft and ductile thermoplastic elastomers.展开更多
Environmental issues such as air pollution and climate change due to excessive fossil fuel burning;plastic pollution and wastewater contamination are a cause of global concern.Bacteria have the ability to not only uti...Environmental issues such as air pollution and climate change due to excessive fossil fuel burning;plastic pollution and wastewater contamination are a cause of global concern.Bacteria have the ability to not only utilize organic contaminants present in wastewater,but also to synthesize bioproducts such as fatty acid methyl esters(FAMEs),the primary molecules in biodiesel and Polyhydroxyalkanoates(PHAs)or bioplastics.The present study aims to investigate production of FAMEs and PHA along with biodegradation of wastewater contaminants by sewage sludge bacteria.Screening of sewage sludge bacteria was done for their lipid/PHA accumulation potential in filter sterilized wastewater by viable colony,fluorescence microscopy and spectrofluorometry methods using nile red staining.For characterization of bacterial FAME and PHA,cultures were subjected to in situ transesterification and analysed using gas chromatography mass spectrometry(GC-MS).A previously reported thermotolerant bacterial strain Bacillus sp.ISTVK1,that showed promising results was further tested for its the potential to produce FAME/PHA along with wastewater contaminant removal by performing physico-chemical analyses,scanning electron microscopy-energy dispersive X-ray(SEM-EDX)spectroscopy and transmission electron microscopy(TEM).The analysis showed the presence of C_(15−18)FAMEs such as Hexadecanoic acid,methyl ester and Tetradecanoic acid 12-methyl ester and PHA such as Pentanoic acid,4-oxo,methyl ester.Physico-chemical analysis of culture supernatant revealed a 92%reduction in COD and the absence of contaminants such as Benzene,1,1’-(2-pentene-1,5-diyl)bis(R.T.=25.42)and 5-(1-Phenyl-cyclopentyl)-[1,3,4]oxadiazole-(R.T.=27.75)from post-treated samples.Results of SEM-EDX and TEM further confirmed bacterial lipid/PHA accumulation and contaminant reduction post-treatment.The potential of the thermotolerant Bacillus sp.ISTVK1 for biodiesel and biopolymer production along with wastewater contaminant removal,as revealed in this study could have future implications in various thermal and polymer industries and wastewater valorization technologies.展开更多
Pseudomonas sp.has been considered one of the most promising microbial platform strains due to its versatile metabolism,enabling the valorization of waste materials into value-added chemical products.As the native pro...Pseudomonas sp.has been considered one of the most promising microbial platform strains due to its versatile metabolism,enabling the valorization of waste materials into value-added chemical products.As the native producer of polyhydroxyal-kanoates(PHAs),the biodegradable biopolyesters,it has been widely engineered by various metabolic engineering tools for the production of PHAs composed of short-chain-length and medium-chain-length monomers with adjustable composition from diverse carbon sources,ranging from pure sugars to crude oils and fatty acids.This review discusses the feasibility of Pseudomonas sp.as the industrial host strain and the recent advances regarding the systems metabolic engineering strategies for PHAs production in Pseudomonas sp.展开更多
Microbial synthesis of functional polymers has become increasingly important for industrial biotechnology. For the first time, it became possible to synthesize controllable composition of poly（3-hydroxyalkanoate） （...Microbial synthesis of functional polymers has become increasingly important for industrial biotechnology. For the first time, it became possible to synthesize controllable composition of poly（3-hydroxyalkanoate） （P3HA） consisting of 3-hydroxydodec- anoate （3HDD） and phenyl group on the side-chain when chromosome of Pseudomonas entomophila was edited to weaken its t-oxidation. Cultured in the presence of 5-phenylvaleric acid （PVA）, the edited P. entomophila produced only homopolymer poly（3-hydroxy-5-phenylvalerate） or P（3HPhV）. While copolyesters P（3HPhV-co-3HDD） of 3-hydroxy-5-phenylvalerate （3HPhV） and 3-hydroxydodecanoate （3HDD） were synthesized when the strain was grown on mixtures of PVA and dodecanoic acid （DDA）. Compositions of 3HPhV in P（3HPhV-co-3HDD） were controllable ranging from 3% to 32% depending on DDDA/PVA ratios. Nuclear magnetic resonance （NMR） spectra clearly indicated that the polymers were homopolymer of P（3HPhV） and random copolymers of 3HPhV and 3HDD. Their mechanical and thermal properties varied dramatically de- pending on the monomer ratios. Our results demonstrated the possibility to produce tailor-made, novel functional PHA using the chromosome edited P. entomophila.展开更多
Polyhydroxyalkanoates(PHA)have been produced by some bacteria as bioplastics for many years.Yet their commercialization is still on the way.A few issues are related to the difficulty of PHA commercialization:namely,hi...Polyhydroxyalkanoates(PHA)have been produced by some bacteria as bioplastics for many years.Yet their commercialization is still on the way.A few issues are related to the difficulty of PHA commercialization:namely,high cost and instabilities on molecular weights(Mw)and structures,thus instability on thermo-mechanical properties.The high cost is the result of complicated bioprocessing associated with sterilization,low conversion of carbon substrates to PHA products,and slow growth of microorganisms as well as difficulty of downstream separation.Future engineering on PHA producing microorganisms should be focused on contamination resistant bacteria especially extremophiles,developments of engineering approaches for the extremophiles,increase on carbon substrates to PHA conversion and controlling Mw of PHA.The concept proof studies could still be conducted on E.coli or Pseudomonas spp.that are easily used for molecular manipulations.In this review,we will use E.coli and halophiles as examples to show how to engineer bacteria for enhanced PHA biosynthesis and for increasing PHA competitiveness.展开更多
Microbial polyhydroxyalkanoates(PHA)have been produced as bioplastics for various purposes.Under the support of China National Basic Research 973 Project,we developed synthetic biology methods to diversify the PHA str...Microbial polyhydroxyalkanoates(PHA)have been produced as bioplastics for various purposes.Under the support of China National Basic Research 973 Project,we developed synthetic biology methods to diversify the PHA structures into homo-,random,block polymers with improved properties to better meet various application requirements.At the same time,various pathways were assembled to produce various PHA from glucose as a simple carbon source.At the end,Halomonas bacteria were reconstructed to produce PHA in changing morphology for low cost production under unsterile and continuous conditions.The synthetic biology will advance the PHA into a bio-and material industry.展开更多
Polyhydroxyalkanoates （PHAs） are a class of biopolyesters that are synthesized intracellularly by microorganisms, mainly by different genera of eubacteria. These biopolymers have diverse physical and chemical proper...Polyhydroxyalkanoates （PHAs） are a class of biopolyesters that are synthesized intracellularly by microorganisms, mainly by different genera of eubacteria. These biopolymers have diverse physical and chemical properties that also classify them as biodegradable in nature and make them compatible to living systems. In the last two decades or so, PHAs have emerged as potential useful materials in the medical field for different applications owing to their unique properties. The lower acidity and bioactivity of PHAs confer them with minimal risk compared to other biopolymers such as poly-lactic acid （PLA） and poly-glycolic acid （PGA）. Therefore, the versatility of PHAs in terms of their non-toxic degradation products, biocompatibility, desired surface modifications, wide range of physical and chemical properties, cellular growth support, and attachment without carcinogenic effects have enabled their use as in vivo implants such as sutures, adhesion barriers, and valves to guide tissue repair and in regeneration devices such as cardiovascular patches, articular cartilage repair scaffolds, bone graft substitutes, and nerve guides. Here, we briefly describe some of the most recent innovative research involving the use of PHAs in medical applications. Microbial production of PHAs also provides the opportunity to develop PHAs with more unique monomer compositions economically through metabolic engineering approaches. At present, it is generally established that the PHA monomer composition and surface modifications influence cell responses.PHA synthesis by bacteria does not require the use of a catalyst （used in the synthesis of other polymers）, which further promotes the biocompatibility of PHA-derived polymers.展开更多
文摘The environmental problems caused by plastics of fossil origin are well known. To reduce harmful impact on the environment, bacterial-based plastics, such as polyhydroxyalkanoates (PHAs), are a promising solution. Microbial PHAs can be produced using abundant and inexpensive agricultural by-products as raw material. In this study, the potential use of Cupriavidus necator 11599 for the bioconversion of cassava starch into biodegradable PHAs was explored. Although Cupriavidus necator 11599 is a well-known PHA producer, it cannot grow directly on starch. Thus, acid hydrolysis was carried out on the starch extracted from cassava peels to obtain fermentable sugars. Optimal concentration of reducing sugars (RSs) was obtained by hydrolysis of cassava peel starch with sulfuric acid concentrations of 0.4 N and 0.6 N, at 95˚C and 4 h. The hydrolyzed starch was used for PHA production in Erlenmeyer flasks using reducing sugars (RSs) concentrations ranging from 10 g/L to 25 g/L. The best RS concentration 20 g/L and 25 g/L gave 85.13% ± 1.17% and 89.01% ± 2.49% of biomass PHA content and biomass concentrations of 8.18 g/L and 8.32 g/L, respectively in 48 hours. This research demonstrates that cassava peel starch as an inexpensive feedstock could be used for PHA production, paving the way for the use of other starchy materials to make bioplastics.
基金financially supported by the State Basic Science Foundation 973 project(Nos.2012CB725201 and 2012CB725200)
文摘Microbial polyhydroxyalkanoates （PHAs） are a family of biopolyesters produced by many wild type and engineered bacteria. PHAs have diverse structures accompanied by flexible thermal and mechanical properties. Combined with their in vitro biodegradation, cell and tissue compatibility, PHAs have been studied for medical applications, especially medical implants applications, including heart valve tissue engineering, vascular tissue engineering, bone tissue engineering, cartilage tissue engineering, nerve conduit tissue engineering as well as esophagus tissue engineering. Most studies have been conducted in the authors＇ lab in the past 20＋ years. Recently, mechanism on PHA promoted tissue regeneration was revealed to relate to cell responses to PHA biodegradation products and cell-material interactions mediated by microRNA. Very importantly, PHA implants were found not to cause carcinogenesis during long-term implantation. Thus, PHAs should have a bright future in biomedical areas.
基金Tsinghua University 985 Project Fund and The State 95 Key Research and Development Fund and Hong Kong Polytechnic University contributed to this project.
文摘Many bacteria have been found to synthesize a family of polyesters termed polyhydroxyalkanoate, abbreviated as PHA. Some interesting physical properties of PHAs such as piezoelectricity, non-linear optical activity, biocompatibility and biodegradability offer promising applications in areas such as degradable packaging, tissue engineering and drug delivery. Over 90 PHAs with various structure variations have been reported and the number is still increasing. The mechanical property of PHAs changes from brittle to flexible to elastic, depending on the side-chainlength of PHA. Many attempts have been made to produce PHAs as biodegradable plastics using various microorganisms obtained from screening natural environments, genetic engineering and mutation. Due to the high production cost, PHAs still can not compete with the nondegradable plastics, such as polyethylene and polypropylene. Various processes have been developed using low cost raw materials for fermentation and an inorganic extraction process for PHA purification. However, a super PHA production strain may play the most critical role for any large-scale PHA production. Our recent study showed that PHA synthesis is a common phenomenon among bacteria inhabiting various locations, especially oil-contaminated soils. This is very important for finding a suitable bacterial strain for PHA production. In fact, PHA production strains capable of rapid growth and rapid PHA synthesis on cheap molasses substrate have been found on molasses contaminated soils. A combination of novel properties and lower cost will allow easier commercialization of PHA for many applications.
基金the DAAD Sandwich Model Scholarships for Master's Students of the IITs and IIMs, 2016/17, who funded the research stay of Mr.Pravesh Tamang in Germany (Personal Ref No: 91635161)
文摘The production of polyhydroxyalkanoates(PHA) from wastewaters using microbial mixed cultures(MMC) has been attracting increased interest because of PHA's biodegradability characteristics. Production of PHA by an MMC enriched with PHA-accumulating bacteria was compared using anaerobically treated and acidified brewery wastewaters under various feeding strategies, namely pulse and batch feed addition. To obtain an enriched MMC, a sequencing batch reactor was inoculated with activated sludge fed with acetate and subjected to aerobic dynamic feeding. The enriched MMC was able to accumulate PHA up to 72.6% of cell dry weight(CDW) with pulse addition of acetate controlled by the dissolved oxygen(DO) concentration in the reactor. In a batch accumulation experiment with acetate,the PHA content achieved(28.5% CDW) was less than that of the pulse feeding strategy with the same amount of acetate(～2000 mg C/L). Using anaerobically treated and acidified brewery wastewater fed in pulses, the maximum PHA accumulated by the enriched MMC was similar for both wastewaters(45% CDW), in spite of the higher volatile fatty acid concentration in acidified brewery wastewater. The pulse feed addition controlled by the DO concentration was difficult to implement for wastewater as compared to acetate because the difference in DO concentration between substrate availability and depletion was low. For the batch addition of acidified wastewater, a slightly lower PHA content(39%CDW) was obtained. These results show that both brewery wastewaters can be utilized for PHA production with a similar maximum PHA storage capacity.
基金supported by the National Natural Science Foundation of China(No.51378142)the Program for New Century Excellent Talents in University(No.NCET-12-0156)+1 种基金the Open Project of the State Key Laboratory of Urban Water ResourceEnvironment(Harbin institute of Technology)(No.2015DX10)
文摘Four sequence batch reactors（SBRs） fed by fermented sugar cane wastewater were continuously operated under the aerobic dynamic feeding（ADF） mode with different configurations of sludge retention time（SRT）, carbon and initial biomass concentrations to enrich polyhydroxyalkanoate（PHA） accumulating mixed microbial cultures（MMCs） from municipal activated sludge.The stability of SBRs was investigated besides the enrichment performance. The microbial community structures of the enriched MMCs were analyzed using terminal restriction fragment length polymorphism（T-RFLP）. The optimum operating conditions for the enrichment process were： SRT of 5 days, carbon concentration of 2.52 g COD/L and initial biomass concentration of3.65 g/L. The best enrichment performance in terms of both operating stability and PHA storage ability of enriched cultures（with the maximum PHA content and PHA storage yield（YPHA/S） of61.26% and 0.68 mg COD/mg COD, respectively） was achieved under this condition. Effects of the SRT, carbon concentration and initial biomass concentration on the PHA accumulating MMCs selection process were discussed respectively. A new model including the segmentation of the enrichment process and the effects of SRT on each phase was proposed.
文摘In this work, sucrose utilizing microbes from soil were screened to evaluate their ability for accumulation of biopolymer of polyhydroxyalkanoate （PHA）. Among 72 isolates were transferred to mineral salt medium （MSM）, 33 strains can be grown on sucrose agar medium. However, only one strain showed a strong black color for Sudan Black and gave positive result for Nile blue A. Identification by 16S rDNA nucleotide sequence homology of the isolate showed very closely to Hydrogenophaga sp. （99% identify）. To consider PHA production, the isolate was grown in the medium containing sucrose as a sole carbon under controlled conditions of 35 ℃ and at pH 7. Maximum dry cell weight （DCW） and PHA production were obtained at 3.61 g/L and 2.41 g/L after 36 and 42 h batch fermentation. Sucrose uptake measured in term of total organic carbon （TOC） showed at 14.73 g within 48 h. The highest PHA was 68.15% （gPHA/gDCW） giving maximum PHA yield （YP/s） of 0.17 （gPHA/gs ） and a productivity of 0.057 gPHA/L.h. This highlights the potential of microbial resources in soil environment and may be an exploitable application for the industrial production of PHA.
基金Supported by the National Basic Research Program of China(2014CB745100)the National Natural Science Foundation of China(21576197)+1 种基金Tianjin Research Program of Application Foundation and Advanced Technology(18JCYBJC23500)Tianjin Key Research&Development Program(16YFXTSF00460)
文摘Concerns about feasibility,separability,settleability,efficiency once hampered studies on polyhydroxyalkanoates(PHAs)production,which mainly focused on single strain microorganism or activated sludge rather than artificial microbial consortia.Here,a medium chain length PHAs(mcl-PHAs)producing Pseudomonas-Saccharomyces consortium with xylose as the main substrate was studied.Mcl-PHAs accumulation increased from 12.69 mg·L^-1 to 152.3 mg·L^-1 without any optimization method.The presence of Saccharomyces cerevisiae,though in a relatively low concentration,improved the sedimentation of cell mass of the mixed culture by 60%.Reasons for better sedimentation of the consortium were complex:first,the length of Pseudomonas putida increased two to three times in the consortium;second,the positive surface charge of P.putida was neutralized by S.cerevisiae;third,the adhesion proteins on the surface of S.cerevisiae interacted with the P.putida.
文摘A total of 5 biochemically characterized lipase positive bacterial strains were screened for Polyhydroxyalkanoates(PHA)production by Nile blue staining and confirmation was done by Sudan Black B.PHA production ability for all strains was optimized followed by time profiling calculation and comparison via using glucose and two plant oils i.e.,canola and mustard oil.Quantitative analysis showed that glucose can serve as a carbon source for maximum biomass(2.5 g/L CDW for strain 5)and PHA production(70.3%for strain 2).PHA produced by strain 2 was further analyzed for its chemical composition and type via Fourier Transform Infrared(FT-IR)spectroscopy.It revealed homopolymer(PHB)and copolymer(PHB-co-PHV)production of PHA(peaks at 1743 cm-1 and 2861 cm-1,respectively)with both canola and mustard oil unlike glucose which produced only homopolymer one i.e.,PHB(peaks at 1110 cm-1,1411 cm-1 and 1650 cm-1).Crystallinity of FT-IR analyzed PHA was calculated using mathematical formulas which showed decrease from glucose to canola to mustard oil.This study revealed that plant oils can serve as better carbon source to produce better quality(ductile and copolymer)PHA.Moreover,16S rRNA gene sequencing analysis showed that strain 1,strain 2,strain 3,strain 4 and strain 5 are Stenotrophomonas sp.N3,Exiguobacterium sp.N4,Exiguobacterium sp.Ch3,Cellulosimicrobium sp.A8 and Klebsiella sp.LFSM2,respectively.
基金Anhui Key Laboratory Foundation of China(No.04swz002)
文摘Polyhydroxyalkanoates （PHAs）, as a candidate for biodegradable plastic materials, can be synthesized by numerous microorganisms. However, as its production cost is high in comparison with those of chemically synthesized plastics, a lot of research has been focused on the efficient production of PHAs using different methods. In the present study, the mutation effects of PHAs production in strain pCB4 were investigated with implantation of low energy ions. It was found that under the implantation conditions of 7.8×10^14 N^＋/cm^2 at 10 keV, a high-yield PHAs strain with high genetic stability was generated from many mutants. After optimizing its fermentation conditions, the biomass, PHAs concentration and PHAs content of pCBH4 reached 2.26 g/L, 1.81 g/L, and 80.08% respectively, whereas its wild type controls were about 1.24 g/L, 0.61 g/L, and 49.20%. Moreover, the main constituent of PHAs was identified as poly-3-hydroxybutyrates （PHB） in the mutant stain and the yield of this compound was increased up to 41.33% in contrast to that of 27.78% in the wild type strain.
基金Sponsored by the National Water Plan(Grant No.2008ZX07317-008)the Stake Key Lab of Urban Water Resource and Environment(Grant No.2010DX02)
文摘Gas chromatography determination of polyhydroxyalkanoates has been common;however,the pretreatment steps are often complex,and gas chromatography operation conditions are not given in detail.In this study,gas chromatography is used for analyzing PHB,PHV and PH2MV,three majors of PHAs in activated sludge.The sample was centrifuged at a speed of 4000 r/min for the separation of floc and supernatant,freezen,and dried for 12 h in vacuum freezing drier;and then transferred to the fridge for freezing to ice and drying for 12 h in vacuum freezing drier;then chloroform and a simple composition digestion solution including methanol,sulfuric acid and benzoic acid was added;digested at 105 ℃ for 6 h;cooled to room temperature,the lower solution of the result can be used for analyzing.Samples were analyzed by gas chromatography with FID detector and auto sampler;the standard curve of standard material shows an excellent linear relationship with correlation coefficients larger than 0.99;the relative standard deviation (RSD) of sludge samples is less than 1%.The recovery rates of each sample are between 95%-105%.The GC analysis time of each PHA sample is shorter than 10 minutes.
基金Supported by the National Science&Technology Pillar Program During the 12th Five-Year Plan Period(2014BAC28B01)Beijing Natural Science Foundation(8112012)
文摘Polyhydroxyalkanoates（PHAs）were synthesized in activated sludge using three types of carbon sources（sodium acetate,sodium propionate and sodium butyrate）,and their characterization were studied.It was shown that the content of PHA synthesized by microorganisms in activated sludge were different.The biggest synthetic amount up to 36.7% of VSS was obtained when sodium acetate was used as carbon source.The polymer yield was lower when using sodium propionate as the carbon source than when using others,with25.1% of VSS,while resulted in an increase of hydroxyvalerate（HV）units produced.The structure and thermal properties of extracted biopolymers were analyzed by scanning electron microscope（SEM）,Fourier transform infrared spectroscopy（FTIR）and themogravimetry（TG）.
文摘Pseudomonas putida KT217 was grown on a complex medium comprised of co-products of the ethanol and biodiesel industries to assess the organism's capability to produce medium-chain-length polyhydroxyalkanoate (mcl-PHA). The growth phase was carried out in a medium containing 400 g/L condensed corn solubles (CCS), supplemented with ammonium hydroxide as a nitrogen source. Following the exponential phase, co-products of the biodiesel industry (soapstock and glycerin) were fed into the reactor to trigger PHA production. When glycerin was added to the bioreactor (75 g/L total addition), the final cell dry weight (CDW) and PHA content were 30 g/L and 31%, respectively. The monomeric composition in the PHA formed was relatively uniform throughout incubation with 3-hydroxydecanoate dominating. When a total of 153 g/L of sunflower soapstock was added to the bioreactor in a fed-batch manner, the final CDW and PHA content were 17 g/L and 17%, respectively. Following addition of soapstock the monomeric composition of the polymer changed dramatically, with the 3-hydroxyoctanoate monomer becoming dominant and greater unsaturation present in the PHA.
基金supported by the Basic Science Research Program of the National Research Foundation of Korea(NRF)funded by the Ministry of Education(RS-2023-00302689 and NRF-2021R1A4A2001403)funded by the Korea Institute of Science and Technology(KIST)Institutional Program(2V09840).
文摘Thick cathodes can overcome the low capacity issues,which mostly hamper the performance of the conventional active cathode materials,used in rechargeable Li batteries.However,the typical slurry-based method induces cracking and flaking during the fabrication of thick electrodes.In addition,a significant increase in the charge-transfer resistance and local cur-rent overload results in poor rate capabilities and cycling stabilities,thereby limiting electrode thickening.In this study,a synergistic dual-network combination strategy based on a conductive nanofibrillar network(CNN)and a nano-bridging amor-phous polyhydroxyalkanoate(aPHA)binder is used to demonstrate the feasibility of constructing a high-performance thick cathode.The CNN and aPHA dual network facilitates the fabrication of a thick cathode(≥250μm thickness and≥90 wt%active cathode material)by a mass-producible slurry method.The thick cathode exhibited a high rate capability and excel-lent cycling stability.In addition,the thick cathode and thin Li metal anode pair(Li//t-NCM)exhibited an optimal energy performance,affording high-performance Li metal batteries with a high areal energy of~25.3 mW h cm^(-2),a high volumetric power density of~1720 W L^(-1),and an outstanding specific energy of~470 W h kg^(-1)at only 6 mA h cm^(-2).
基金supported by the National Natural Science Foundation of China(No.52173093)Peking University Ge Li and Ning Zhao Life Science Research Fund for Young Scientists。
文摘Poly(3-hydroxybutyrate),a crucial member of the large biodegradable polyhydroxyalkanoate family,suffers from its brittleness.To enhance its performance,we employed a straightforward approach involving the ring-opening copolymerization of racemic-β-butyrolactone(rac-β-BL)andβ-propiolactone(β-PL)using the syndio-selective amino-alkoxy-bis(phenolate)-yttrium complex as a catalyst,thanks to the excellent ductility of poly(3-hydroxypropionate).Control over the rac-β-BL/β-PL feeding ratios and polymerization time yielded random or block copolymers with tunable thermal and mechanical properties comparable to traditional fossil-based plastics.Furthermore,we achieved one-pot synthesis of hard-soft-hard triblock copolymers by exploiting monomers’different copolymerization rates and a bifunctional initiator,thus transforming polyhydroxyalkanoates from hard and tough plastics to soft and ductile thermoplastic elastomers.
文摘Environmental issues such as air pollution and climate change due to excessive fossil fuel burning;plastic pollution and wastewater contamination are a cause of global concern.Bacteria have the ability to not only utilize organic contaminants present in wastewater,but also to synthesize bioproducts such as fatty acid methyl esters(FAMEs),the primary molecules in biodiesel and Polyhydroxyalkanoates(PHAs)or bioplastics.The present study aims to investigate production of FAMEs and PHA along with biodegradation of wastewater contaminants by sewage sludge bacteria.Screening of sewage sludge bacteria was done for their lipid/PHA accumulation potential in filter sterilized wastewater by viable colony,fluorescence microscopy and spectrofluorometry methods using nile red staining.For characterization of bacterial FAME and PHA,cultures were subjected to in situ transesterification and analysed using gas chromatography mass spectrometry(GC-MS).A previously reported thermotolerant bacterial strain Bacillus sp.ISTVK1,that showed promising results was further tested for its the potential to produce FAME/PHA along with wastewater contaminant removal by performing physico-chemical analyses,scanning electron microscopy-energy dispersive X-ray(SEM-EDX)spectroscopy and transmission electron microscopy(TEM).The analysis showed the presence of C_(15−18)FAMEs such as Hexadecanoic acid,methyl ester and Tetradecanoic acid 12-methyl ester and PHA such as Pentanoic acid,4-oxo,methyl ester.Physico-chemical analysis of culture supernatant revealed a 92%reduction in COD and the absence of contaminants such as Benzene,1,1’-(2-pentene-1,5-diyl)bis(R.T.=25.42)and 5-(1-Phenyl-cyclopentyl)-[1,3,4]oxadiazole-(R.T.=27.75)from post-treated samples.Results of SEM-EDX and TEM further confirmed bacterial lipid/PHA accumulation and contaminant reduction post-treatment.The potential of the thermotolerant Bacillus sp.ISTVK1 for biodiesel and biopolymer production along with wastewater contaminant removal,as revealed in this study could have future implications in various thermal and polymer industries and wastewater valorization technologies.
基金supported by the Development of synthetic microbial platform systems for one step-one pot synthesis of next-generation biodegradable biopolymers(NRF-2022M3J4A1053696)from National Research Foundation(NRF)supported by the Korean Ministry of Science and ICT(MSIT)by the Development of next-generation biorefinery platform technologies for leading bio-based chemicals industry project(NRF-2022M3J5A1056072 and NRF-2022M3J5A1056117)from NRF supported by MSIT.
文摘Pseudomonas sp.has been considered one of the most promising microbial platform strains due to its versatile metabolism,enabling the valorization of waste materials into value-added chemical products.As the native producer of polyhydroxyal-kanoates(PHAs),the biodegradable biopolyesters,it has been widely engineered by various metabolic engineering tools for the production of PHAs composed of short-chain-length and medium-chain-length monomers with adjustable composition from diverse carbon sources,ranging from pure sugars to crude oils and fatty acids.This review discusses the feasibility of Pseudomonas sp.as the industrial host strain and the recent advances regarding the systems metabolic engineering strategies for PHAs production in Pseudomonas sp.
基金supported by the National High Technology Research and Development Program of China(2012AA023102 to Liu Lei,Guo Kai and Wu Qiong)the National Basic Research Program of China(2012CB725201 to Chen GuoQiang and Chen JinChun,2012CB725204 to Guo Kai and Wu Qiong)National Natural Science Foundation of China(31270146 to Chen GuoQiang)
文摘Microbial synthesis of functional polymers has become increasingly important for industrial biotechnology. For the first time, it became possible to synthesize controllable composition of poly（3-hydroxyalkanoate） （P3HA） consisting of 3-hydroxydodec- anoate （3HDD） and phenyl group on the side-chain when chromosome of Pseudomonas entomophila was edited to weaken its t-oxidation. Cultured in the presence of 5-phenylvaleric acid （PVA）, the edited P. entomophila produced only homopolymer poly（3-hydroxy-5-phenylvalerate） or P（3HPhV）. While copolyesters P（3HPhV-co-3HDD） of 3-hydroxy-5-phenylvalerate （3HPhV） and 3-hydroxydodecanoate （3HDD） were synthesized when the strain was grown on mixtures of PVA and dodecanoic acid （DDA）. Compositions of 3HPhV in P（3HPhV-co-3HDD） were controllable ranging from 3% to 32% depending on DDDA/PVA ratios. Nuclear magnetic resonance （NMR） spectra clearly indicated that the polymers were homopolymer of P（3HPhV） and random copolymers of 3HPhV and 3HDD. Their mechanical and thermal properties varied dramatically de- pending on the monomer ratios. Our results demonstrated the possibility to produce tailor-made, novel functional PHA using the chromosome edited P. entomophila.
基金This research was financially supported by a grant from Ministry of Sciences and Technology(Grant No.2016YFB0302504)grants from National Natural Science Foundation of China(Grant No.31430003)Tsinghua President Fund also supported this project(Grant No.2015THZ10).
文摘Polyhydroxyalkanoates(PHA)have been produced by some bacteria as bioplastics for many years.Yet their commercialization is still on the way.A few issues are related to the difficulty of PHA commercialization:namely,high cost and instabilities on molecular weights(Mw)and structures,thus instability on thermo-mechanical properties.The high cost is the result of complicated bioprocessing associated with sterilization,low conversion of carbon substrates to PHA products,and slow growth of microorganisms as well as difficulty of downstream separation.Future engineering on PHA producing microorganisms should be focused on contamination resistant bacteria especially extremophiles,developments of engineering approaches for the extremophiles,increase on carbon substrates to PHA conversion and controlling Mw of PHA.The concept proof studies could still be conducted on E.coli or Pseudomonas spp.that are easily used for molecular manipulations.In this review,we will use E.coli and halophiles as examples to show how to engineer bacteria for enhanced PHA biosynthesis and for increasing PHA competitiveness.
基金the State Basic Science Foundation 973(Grant no.2012CB725201)National Natural Science Foundation of China(Grant no.31430003 and 31270146).
文摘Microbial polyhydroxyalkanoates(PHA)have been produced as bioplastics for various purposes.Under the support of China National Basic Research 973 Project,we developed synthetic biology methods to diversify the PHA structures into homo-,random,block polymers with improved properties to better meet various application requirements.At the same time,various pathways were assembled to produce various PHA from glucose as a simple carbon source.At the end,Halomonas bacteria were reconstructed to produce PHA in changing morphology for low cost production under unsterile and continuous conditions.The synthetic biology will advance the PHA into a bio-and material industry.
文摘Polyhydroxyalkanoates （PHAs） are a class of biopolyesters that are synthesized intracellularly by microorganisms, mainly by different genera of eubacteria. These biopolymers have diverse physical and chemical properties that also classify them as biodegradable in nature and make them compatible to living systems. In the last two decades or so, PHAs have emerged as potential useful materials in the medical field for different applications owing to their unique properties. The lower acidity and bioactivity of PHAs confer them with minimal risk compared to other biopolymers such as poly-lactic acid （PLA） and poly-glycolic acid （PGA）. Therefore, the versatility of PHAs in terms of their non-toxic degradation products, biocompatibility, desired surface modifications, wide range of physical and chemical properties, cellular growth support, and attachment without carcinogenic effects have enabled their use as in vivo implants such as sutures, adhesion barriers, and valves to guide tissue repair and in regeneration devices such as cardiovascular patches, articular cartilage repair scaffolds, bone graft substitutes, and nerve guides. Here, we briefly describe some of the most recent innovative research involving the use of PHAs in medical applications. Microbial production of PHAs also provides the opportunity to develop PHAs with more unique monomer compositions economically through metabolic engineering approaches. At present, it is generally established that the PHA monomer composition and surface modifications influence cell responses.PHA synthesis by bacteria does not require the use of a catalyst （used in the synthesis of other polymers）, which further promotes the biocompatibility of PHA-derived polymers.
