Phylogenetic structure of bacterioplankton in water bodies of the Kuibyshev Reservoir basin during the period of mass development of cyanobacteria

The phylogenetic structure of the bacterioplankton of the Usa Bay and the adjacent aquatory of the Kuibyshev Reservoir, as well as three hydrologically connected urban lakes of the Kaban system (Kazan), was analyzed using the results of high-throughput sequencing of the V3‒V4 hypervariable region of the 16S ribosomal RNA gene. In the studied water objects, mass cyanobacterial development was observed, dominated by members of the Aphanizomenon / Dolichospermum and Cyanobium phylogenetic lines and the genus Planktothrix. Alpha- and betaproteobacteria dominated in the heterotrophic bacterioplankton of all stations. A significant proportion of its composition was made up of mixotrophic bacteria with the rhodopsin type of photosynthesis (for example, Ca. Fonsibacter, Ca. Nanopelagicus, Ca. Planctophila). A characteristic feature of the studied samples is a high proportion of bacteria of PVC superphylum, especially Planctomycetota. An assessment was made of the dependence of the composition and structure of bacterioplankton on the composition of the dominant cyanobacterial complexes, and groups of heterotrophic bacteria associated with various cyanobacteria were identified. The most numerous group is formed around Aphanizomenon ‒ Dolichospermum ‒ Microcystis and mainly consists of bacteria that are part of the phycosphere of colonial cyanobacteria, as well as representatives of the PVC superphylum. Two small groups are formed around Limnothrix redekei and Cyanobium rubescens and consist of typical planktonic bacteria, belonging mainly to the order Flavobacteriales and the family Nanopelagicaceae.