Distribution, community structure and metabolic potential of bacterioplankton in a small boreal lake: Microscopy-based survey and 16S rRNA-based DNA metabarcoding

Bacteria are numerous and diverse organisms that have a significant impact on the functioning of aquatic ecosystems. On the vast territory of the West Siberian Lowland (Russia) there are many rivers, lakes and bogs, the microbial communities of which are almost unexplored. Here, we report the study results on the distribution, diversity, community structure and functions of bacterioplankton in the pelagic and littoral zones of one of the lakes, located in this region (Lake Kuchak) obtained using microscopic techniques and 16S rRNA gene metabarcoding. The high total bacterial abundance and biomass, the diversity indices, and the high number of Actinobacteria amplicon sequence variants (ASVs), along with the relatively low number of Betaproteobacteria ASVs, indicate the eutrophication of the lake, especially in its overgrown littoral zone. Similar bacterial communities developed in the pelagic and littoral zones due to similar environmental conditions in these habitats of this small and shallow lake. Nevertheless, there were some differences between the pelagic and littoral zones, causing differences in the bacterial communities of these zones more in size and morphological structure than in taxonomic composition. Comparative analysis of the bacterial metabolic ways showed the higher functional potential in the pelagic zone compared to the littoral one. Signs of methylotrophic and methanotrophic activities, as well as pollutant biodegradation potential of the bacterioplankton were identified. The bacterial distribution and community composition indicates the input of organic substances into the lake from the watershed, but also shows the community resistance to allochthonous microorganisms. Alpha diversity indices, distribution of taxonomic groups and some other results indicate deterioration of water quality in the overgrown littoral zone.