Periphytic biofilms exist widely in paddy fields, but their influences on the hydrolysis of organic phosphorus(P) have rarely been investigated. In this study,a periphytic biofilm was incubated in a paddy soil solutio...Periphytic biofilms exist widely in paddy fields, but their influences on the hydrolysis of organic phosphorus(P) have rarely been investigated. In this study,a periphytic biofilm was incubated in a paddy soil solution, and hydrolysis kinetic parameters(half-saturation constant(Km) and maximum catalytic reaction rate(Vmax)), optimal environmental conditions, substrate specificity, and response to different P regimes of the phosphatase activities in the periphytic biofilm were determined, in order to characterize extracellular phosphatase activities in periphytic biofilms from paddy fields. The results indicated that the periphytic biofilm could produce an acid phosphomonoesterase(PMEase), an alkaline PMEases, and a phosphodiesterase(PDEase). These three phosphatases displayed high substrate affinity, with Km values ranging from 141.03 to 212.96 μmol L^(-1). The Vmax/Km ratios for the phosphatases followed the order of alkaline PMEase > acid PMEase > PDEase, which suggested that the PMEases, especially the alkaline PMEase, had higher catalytic efficiency. The optimal pH was 6.0 for the acid PMEase activity and 8.0 for the PDEase activity, and the alkaline PMEase activity increased with a pH increase from 7.0 to 12.0. The optimal temperature was 50℃ for the PMEases and 60℃ for the PDEase. The phosphatases showed high catalytic efficiency for condensed P over a wide pH range and for orthophosphate monoesters at pH 11.0, except for inositol hexakisphosphate at pH 6.0. The inorganic P supply was the main factor in the regulation of phosphatase activities. These findings demonstrated that the periphytic biofilm tested had high hydrolysis capacity for organic and condensed P,especially under P-limited conditions.展开更多
Heterotrophic bacterial production and respiration,two important contributors to carbon cycling,play an important role in global biogeochemical cycles.However,recent research suggests that these two processes may be d...Heterotrophic bacterial production and respiration,two important contributors to carbon cycling,play an important role in global biogeochemical cycles.However,recent research suggests that these two processes may be decoupled,and the underlying changes in community structure and their interactions remain unclear.In this study,two research expeditions to the North Pacific Subtropical Gyre(NPSG)during the summer and winter of 2020–2021 revealed seasonal shifts in bacterial metabolism and community structure in response to environmental factors.The findings indicated notable seasonal fluctuations in bacterial abundance and production in the surface waters.Both peaked in winter compared to summer.Alterations in bacterial abundance that were further evident at the community level demonstrated significant seasonal differences in bacterial community structure and diversity and revealed,in particular,the intricacy of the networks and interactions among bacterial communities in winter.Bacterial respiration displayed no significant seasonal variations and was decoupled from bacterial abundance and production.The implication was that bacterial production did not directly dictate bacterial respiration.Specific taxa exerted a more substantial influence on bacterial respiration,potentially including groups with high respiration rates but relatively low abundance,thus challenging the notion that highly abundant taxa are invariably the most metabolically active.Moreover,the interplay between different bacterial taxa and their interactions may also impact the overall strength of bacterial community respiration.These findings significantly enhance our understanding of the decoupling between bacterial production and respiration,which is crucial for unraveling the complex mechanisms underlying carbon cycling and energy flow in marine ecosystems.展开更多
基金supported by the State Key Basic Research Program of China (No. 2015CB158200)the National Natural Science Foundation of China (No. 41877102)+1 种基金the Interdisciplinary Innovation Team of Chinese Academy of Sciences (CAS)the Youth Innovation Promotion Association of CAS (No. 2014272)。
文摘Periphytic biofilms exist widely in paddy fields, but their influences on the hydrolysis of organic phosphorus(P) have rarely been investigated. In this study,a periphytic biofilm was incubated in a paddy soil solution, and hydrolysis kinetic parameters(half-saturation constant(Km) and maximum catalytic reaction rate(Vmax)), optimal environmental conditions, substrate specificity, and response to different P regimes of the phosphatase activities in the periphytic biofilm were determined, in order to characterize extracellular phosphatase activities in periphytic biofilms from paddy fields. The results indicated that the periphytic biofilm could produce an acid phosphomonoesterase(PMEase), an alkaline PMEases, and a phosphodiesterase(PDEase). These three phosphatases displayed high substrate affinity, with Km values ranging from 141.03 to 212.96 μmol L^(-1). The Vmax/Km ratios for the phosphatases followed the order of alkaline PMEase > acid PMEase > PDEase, which suggested that the PMEases, especially the alkaline PMEase, had higher catalytic efficiency. The optimal pH was 6.0 for the acid PMEase activity and 8.0 for the PDEase activity, and the alkaline PMEase activity increased with a pH increase from 7.0 to 12.0. The optimal temperature was 50℃ for the PMEases and 60℃ for the PDEase. The phosphatases showed high catalytic efficiency for condensed P over a wide pH range and for orthophosphate monoesters at pH 11.0, except for inositol hexakisphosphate at pH 6.0. The inorganic P supply was the main factor in the regulation of phosphatase activities. These findings demonstrated that the periphytic biofilm tested had high hydrolysis capacity for organic and condensed P,especially under P-limited conditions.
基金supported by the National Natural Science Foundation of China[grant numbers 42122044,42130401,41890803]。
文摘Heterotrophic bacterial production and respiration,two important contributors to carbon cycling,play an important role in global biogeochemical cycles.However,recent research suggests that these two processes may be decoupled,and the underlying changes in community structure and their interactions remain unclear.In this study,two research expeditions to the North Pacific Subtropical Gyre(NPSG)during the summer and winter of 2020–2021 revealed seasonal shifts in bacterial metabolism and community structure in response to environmental factors.The findings indicated notable seasonal fluctuations in bacterial abundance and production in the surface waters.Both peaked in winter compared to summer.Alterations in bacterial abundance that were further evident at the community level demonstrated significant seasonal differences in bacterial community structure and diversity and revealed,in particular,the intricacy of the networks and interactions among bacterial communities in winter.Bacterial respiration displayed no significant seasonal variations and was decoupled from bacterial abundance and production.The implication was that bacterial production did not directly dictate bacterial respiration.Specific taxa exerted a more substantial influence on bacterial respiration,potentially including groups with high respiration rates but relatively low abundance,thus challenging the notion that highly abundant taxa are invariably the most metabolically active.Moreover,the interplay between different bacterial taxa and their interactions may also impact the overall strength of bacterial community respiration.These findings significantly enhance our understanding of the decoupling between bacterial production and respiration,which is crucial for unraveling the complex mechanisms underlying carbon cycling and energy flow in marine ecosystems.
