Community Structure And Nitrogen Removal Characteristics Of Aerobic Anoxygenic Photosynthetic Bacteria In Drinking Water Reservoirs

Aerobic anoxygenic photosynthetic bacteria（AAPB）have become a hot topic in the field of aquatic microbial ecology and play an important role in water material circulation and energy flow.They are unique photoheterotrophs which can use bacteriochlorophyll-containing to harvest light energy for photosynthesis without oxygen production but also absorb organic matter from environment to maintain cell growth and metabolism.They are widely distributed in typical aquatic ecosystems such as various oceanic regions oceans,lakes and river estuaries with high abundance.However,the related reports of AAPB in stratified reservoir waters were few.In recent years,more and more AAPB species have been discovered and reported,based on phylogenetic analysis of puf M gene,most AAPB belong to alpha-,beta-,and gamma-proteobacteria,and their abundance and diversity show significant differences with different habitats.In order to investigate the community structure and nitrogen removal characteristics of AAPB in drinking water reservoirs,Jinpen and Lijiahe drinking water reservoir water bodies were selected.Based on the analysis of water quality parameters,quantitative real-time PCR and Illumina Mi Seq high-throughput sequencing technique targeting the puf M gene were applied to this study.Furthermore,the redundancy analysis was used to reveal the influence of environmental factors on their community structure.The results have guiding significance for parsing the spatial and temporal variability of AAPB abundance and diversity in stratified reservoir and simultaneously provide a theoretical basis for exploring exploring the driving factors of AAPB population structure.The nitrogen removal efficiencies of plenty of mix cultured AAPB,isolated and screened from the source water,were calculated to obtain three groups of the mix cultured AAPB with high efficiency of nitrogen and carbon removal performance.Successivly,DNA sequencing technology based on puf M gene was used to analyze the comuunity structure of mix cultured AAPB,and combined with the network method to reveal the co-interaction patterns and interactions among them.Additionally,the nitrogen and cabon removal efficiencies of source water by three groups of AAPB flora were calculated to evaluate their adaptabilities and applicabilities in source water.The fingings include:（1）The results showed that the AAPB abundance ranged from（6.70±0.43）×10³to（2.69±0.15）×10⁴ copies m L^-1 in Jinpen reservoir during the natural mixing period,the dominant AAPB genus were Bradyrhizobium sp.and Methylobacterium sp.There was a strong interaction between AAPB genera,and their community structures were mainly affected by water temperature（T）,total nitrogen（TN）,nitrate nitrogen（NO₃^--N）and light intensity and comprehensively regulated by environmental factors.（2）The sequencing results based on puf M gene showed that the community structure composition and distribution of AAPB were significantly different in Jinpen reservoir during thermal stratification and stabilization period,mainly including Bradyrhizobium sp.,Methylobacterium sp.,Sphingomonas sp.,and Limnohabitans sp.,and the spatial and temporal distribution of abundance was extremely different.Network analysis results showed that the interaction between AAPB genera was complex and changeable.（3）It was found that the AAPB composition and abundance of Lijiahe reservoir were significantly different from that of Jinpen reservoir,and the most abundant AAPB were Methylobacterium sp.and Limnohabitans sp..In addition,AAPB genus with high abundance has also been detected,mainly including Blastomonas sp.,Pseudomonas sp.,and Bradyrhizobium sp.,and their interactions are complicated.（4）Three groups of mix-cultured AAPB named as LH19,LB20 and LH21,with high efficiency of nitrogen and carbon removal performance were isolated successfully from source water.The results showed that their total dissoved nitrogen（TDN）removal efficiencies were 87.25%,87.30%,and 88.45%,respectively.Moreover,their NO₃^--N removal efficiencies were 93.68%,93.37%,and 94.97%,respectively.Additionally,their dissolved organic carbon（DOC）removal efficiencies were 99.11%,99.14%,and 99.30%,respectively.The puf M gene sequencing observed that the community composition and relative abundance of AAPB changed over the culture time.For example,for LB20,Vradyrhizobium sp.was the most dominant at 9 h,with the persentage of 39.50%,while Roseateles depolymerans became the most abundant at 48 h,accounting for 42.10%.Network analysis indicated that the co-occurrence and interaction of different AAPB genera was complex.Similarly,for LB20,Limnohabitans planktonicus was positive correlated with Methylobacterium sp.,while was negative correlated with Rubrivivax gelatinosu.This co-occurrence will drive the TDN and NO₃^--N removal performance by mix-cultured AAPB.（5）The removal efficiencies of total dissolved nitrogen（TDN）of source water by LH19,LB20,and LH21 were 24.89%,27.04%,and 22.33%,respectively;the removal efficiencies of NO₃^--N were 31.00%,35.60,and 30.40%,respectively;and the removal efficiencies of DOC was 28.22%,31.17%,and 25.59%,respectively,significantly higher than some reported aerobic denitrifying bacteria.