Large diversity changes among aerobic anoxygenic phototrophs in a freshwater lake. Large diversity changes among aerobic anoxygenic phototrophs in a freshwater lake

Aerobic anoxygenic photoheterotrophic (AAP bacteria) bacteria represent a functional group that harvests light energy using bacteriochlorophyll-containing photosynthetic reaction centers. They are an active and rapidly growing component of freshwater bacterioplankton, with the highest numbers observed usually in summer. High diversity of freshwater AAP bacteria has been observed in lakes, but their seasonal dynamics remain unknown. Here, we analyzed, for the first time, the temporal changes in the composition of phototrophic community in an oligo-mesotrophic freshwater lake using amplicon sequencing of the pufM marker gene. The AAP bacteria community was dominated by phototrophic Gammaproteobacteria and Alphaproteobacteria, with smaller contribution of phototrophic Chloroflexota and Gemmatimonadota. Phototrophic Eremiobacteriota or members of Myxococcota were not detected. Interestingly, some AAP bacteria groups, such as Limnohabitans, Rhodoferax, Rhodobacterales or Rhizobiales, were constantly present over the sampling period, while others, such as Sphingomonadales, Rhodospirillales or Caulobacterales appeared only transiently. The environmental factors that best explained the seasonal changes in AAP bacteria community were temperature, concentrations of oxygen and dissolved organic matter.