The Structure And Ecological Function Differentiation Of Bacterioplankton Community With Different Lifestyles In Poyang Lake

In the lake ecosystem,bacterioplankton often competes for space and nutrients and occupies different microecological niches through a variety of pathways,resulting in two different lifestyles of bacterioplankton:particle-attached bacteria（PAB）and free-living bacteria（FLB）.The different lifestyles may lead to differences in their community structure and ecological functions.However,most of the studies have focused on analyzing the community structure of bacterioplankton with different lifestyles,while the linkage between lifestyles and ecological functions is still poorly understood.Therefore,this study focused on the community structure and ecological function differentiation of bacterioplankton with different lifestyles in freshwater lakes,and explored the main factors affecting the differentiation of planktonic lifestyle and ecological functions.In order to scientifically analyze the influence of planktonic lifestyle on biogeochemical cycles in freshwater lake ecosystems.In this study,surface water,overlying water and sediment samples were collected from the whole hydrological cycle（water-rising period,high-water-level period,water-declining period and low-water-level period）of Poyang Lake,the largest freshwater lake in China.Two different lifestyles of bacterioplankton:particle-attached bacteria（PAB）and free-living bacteria（FLB）were obtained by graded filtration.The community structures and the abundance of relevant functional genes involved in C,N,P and S metabolism of PAB and FLB in surface and overlying water were analyzed by high-throughput sequencing technology and fluorescence quantitative PCR,and compared with the sediment bacterial community.And on the basis of these,the effects of environmental parameters on the lifestyle and ecological functions were explored by redundancy analysis.The main conclusions obtained were as follows:（1）There were significant differences in the diversity,community composition and ecological functions of the planktonic bacterial communities with different lifestyles in the surface water of Poyang Lake.Forαdiversity,FLB community diversity was significantly lower than that of PAB community.For community composition,the relative abundance of Proteobacteria,Bacteroidota,Cyanobacteria,Acidobacteriota,Planctomycetes,Chloroflexi and Gemmatimonadetes were significantly higher in the PAB community,while the relative abundance of Actinobacteriota and Firmicutes were significantly higher in the FLB community;at the genus level,Mesorhizobium,Cyanobium＿PCC-6307,Flavobacterium,Rhizobiales＿Incertae＿Sedis＿uncultured,Novosphingobium and Pseudorhodobacter had significantly higher relative abundance in the PAB community,while hgc Iclade,Sporichthyaceae＿ge,Limnohabitans,Methylobacterium,Sphingomonas and Polynucleobacter had significantly higher relative abundance in the FLB community.Functional predictions based on the FAPROTAX database showed that both PAB and FLB communities in surface water contained high abundance of chemoheterotrophic and aerobic chemoheterotrophic functions,in addition to a large number of phototrophic and nitrate reducing functions in PAB communities,while FLB communities also contained some animal symbionts,human-associated pathogens,the presence of small amounts of aromatic compounds,hydrocarbons,aliphatic non-methane hydrocarbons,and aromatic hydrocarbon degradation functions,in addition to some methylotrophic functions,especially methanol oxidation.To validate the functional predictions,we quantified the functional genes of PAB and FLB communities in the surface water.We found that the PAB community played a more important role in carbon fixation,methanogenesis,methane oxidation,and ammonia oxidation functions,while the FLB community played a more important role in methanol oxidation,nitrite oxidation,and nitrous oxide reduction.Redundancy analysis showed that,for the surface water,the environmental variables that had the greatest influence on the structure of the PAB community were Tm（Temperature）,followed by DO（Dissolved oxygen）,NH₄⁺-N（Ammonia nitrogen）,and NO₃^--N（Nitrate nitrogen）,and the environmental variables that significantly affected their ecological functions were NH₄⁺-N,AP（Available phosphorus）,Cond（Conductivity）,and TP（Total phosphorus）.The environmental variables that also had the greatest influence on the structure of the FLB community were Tm,followed by NO₃^--N,DTN（Total dissolved nitrogen）,and TP,and the environmental variables that had a major impact on their ecological functions were NH₄⁺-N,Cond,p H,and Tm.（2）There were also significant differences in the diversity,community composition and ecological functions of the planktonic bacterial communities with different lifestyles in the overlying water of Poyang Lake.Forα-diversity,PAB community diversity was significantly higher than FLB community.For community composition,the relative abundance of Bacteroidota,Acidobacteriota,Chloroflexi,Nitrospirota and Myxococcota were significantly higher in the PAB community,while the relative abundance of Actinobacteriota and Patescibacteria were significantly higher in the FLB community;at the genus level,the relative abundance of Flavobacterium was significantly higher in the PAB community,while the relative abundance of Enhydrobacter,Limnohabitans,CL500-29marinegroup and hgc Iclade had significantly higher relative abundance in the FLB community.The functional predictions based on the FAPROTAX database showed that both PAB and FLB communities in the overlying water contained high abundance of chemoenergetic heterotrophic and aerobic chemoenergetic heterotrophic functions,in addition to a large number of phototrophic functions in the PAB community,while the FLB community also contained some human-associated pathogens,a small amount of hydrocarbon degradation functions,in addition to some methylotrophic functions,and especially methanol oxidation.To validate the functional predictions,we quantified the functional genes of PAB and FLB communities in the overlying water.We found that the PAB community played more important roles in carbon fixation,methanogenesis,methane oxidation,nitrogen fixation,nitrite oxidation,and ammonia oxidation functions,while the FLB community played a more important role in methanol oxidation.Redundancy analysis showed that,for the overlying water,the environmental variables that had the greatest impact on the structure of the PAB community were Tm,followed by Cond,AP,and DTP（Total dissolved phosphorus）,and the environmental variables that had a major impact on their ecological functions were NH₄⁺-N,TP,AP and SD（Transparency）.The environmental variables that had the greatest influence on the structure of the FLB community were also Tm,followed by SD,Cond and p H,and the environmental variables that had a major impact on their ecological functions were p H,Chl a（Chlorophyll a）,and NO₃^--N.（3）In the vertical direction,we found that both surface water and overlying water showed great similarity in bacterial community diversity,community composition and ecological functions for both PAB and FLB communities,with significant differences from sediment bacterial communities.For community diversity,the sediment bacterial community diversity was significantly higher than that of the planktonic bacterial community.In addition,the PAB community diversity in the overlying water was significantly higher than that in the surface water,which was closer to that of the sediment bacterial community.For the community composition,Proteobacteria and Bacteroidetes may be the dominant phyla in the PAB community,while the FLB community is enriched with more Actinobacteria,and the sediment bacterial community contains more Acidobacteria,Chloroflexi,MBNT15,Nitrospirae,Desulfobacterota,Myxococcota,Latescibacterota,Gemmatimonadota and Sva0485.At the genus level,the PAB community in surface and overlying waters contained a large number of Flavobacterium and Cyanobium＿PCC-6307 in surface and overlying waters contained a large number of hgc I＿clade,while the hgc I＿clade was abundant in the FLB community.In addition,we found that the sediment bacterial community contained higher abundance of SC-I-84.The results of functional prediction showed that both in surface water and overlying water,the PAB communities contained a large number of phototrophic functions,the FLB communities contain some animal symbionts,human-associated pathogens,and some methanotrophic functions,especially methanol oxidation,while the sediment bacterial community contains some fermentation functions,nitrate reduction functions,and aromatic compound degradation functions.In summary,our study found that the bacterioplankton with different lifestyles（free-living bacteria and particle-attached bacteria）in Poyang Lake are differentiated in community structure and ecological functions.The free-living bacterial community contains a large number of Actinobacteria（especially hgc I＿clade genus）to utilize small molecules of dissolved organic matter in the water column,mainly performing methanol oxidation function,nitrite oxidation and nitrous reduction.The particle-attached bacterial community contains a large number of Flavobacterium and Cyanobium＿PCC-6307 to enable it to better attach to particulate organic matter and obtain more carbon sources,mainly performing carbon fixation,methanogenesis and methane oxidation functions as well as nitrogen fixation and ammonia oxidation functions.In addition,we also found that the sediment bacterial community contained a large number of SC-I-84 genus（belongs to the phylum Proteobacteria）,also contained higher abundance of carbon fixation and nitrogen fixation genes.The results of this study elucidate the differentiation in community structure and ecological functions of bacterioplankton with different lifestyles in the ecosystem of Poyang Lake,which is important for the comprehensive study of microbial-mediated ecological processes and biogeochemical cycles in the lake environment.