Wide distribution of anaerobic ammonium‐oxidizing bacteria in the water column of the South China Sea: Implications for their survival strategies

Aim Anammox bacteria are widely distributed in various environments, but the community composition and survival strategies of anammox bacteria in oligotrophic, deep-sea water rich in dissolved oxygen (DO) remain unknown. We aimed to understand the distribution of anammox bacteria in the water columns of the South China Sea (SCS). Time period Three cruises were in October 2014, October 2015 and September 2016, respectively. Location Six water columns were obtained in the SCS, China (E 111-120 degrees, N 16-22 degrees). Methods The diversity and community composition of anammox bacteria were investigated through a high-throughput sequencing technique targeting the anammox 16S rRNA gene. Results Unexpectedly, phylogenetic analysis showed thatCa. Brocadia (78.35%) was the dominant genus whileCa. Scalindua and unclassified species accounted for 12.62% and 9.03%, respectively. The highest diversity of anammox bacteria and concentrations of particulate organic matter (POM) were simultaneously observed in the 50-200 m layer, suggesting that particles may be a favourable niche for anammox bacteria. The wide distribution of anammox bacteria in the DO-rich sea waters suggests two possible survival strategies: one strategy is attaching to particles and using anaerobic anammox metabolism to produce energy, and the other strategy is free-living and using aerobic metabolism to produce energy. Main conclusions A high diversity of anammox bacteria was found in the aerobic water columns, andCa. Brocadia was the clearly dominant genus. Furthermore, anammox microbes could improve their viability by switching their metabolic pathways between anaerobic and aerobic conditions. Overall, our study has improved the understanding of the distribution and survival strategies of anammox communities in an aerobic marine environment and could provide new ideas for engineering applications in wastewater treatment with anammox technology.