The Vertical Profile and Diversity Within the Bacterioplankton Assemblages in a Deep Freshwater Lake (Lake Biwa, Japan)

Holomictic mesotrophic lakes, characterized by oxygenated hypolimnion due to seasonal mixing of their water layers, host microbial assemblages with diversity and community compositions strongly shaped by the constant recycling of nutrients. However, other studies showed occurrences of hypolimnion-specific lineages, distinct from adjacent epilimnion in such lakes. The study focused on Lake Biwa, a tectonic mesotrophic lake in Japan, to spatially elucidate bacterial assemblages between the epilimnion and oxygenated hypolimnion. 16S rRNA gene analysis revealed dominance of bacterial members belonging to Pseudomonadota, Bacillota and Bacteroidota throughout the water column, while other lineages such as Bdellovibrionota, Kapabacteria and WGS were not detected in the epilimnion and were solely hypolimnion-specific in their occurrences. This study serves to further corroborate earlier investigations that have shown bacterioplankton community differences in the vertical distribution of deep-water lakes.