Phylogenetic Diversity of Prokaryotic Communities of the Upper Sediment Layers of the Kandalaksha Gulf, White Sea

Abstract—Microbial communities of the sediments of the Kandalaksha Gulf (White Sea) remain insufficiently studied. While the data on the rates of some microbial processes are available, very little is known of the microorganisms inhabiting these sediments. In the present work, high-throughput sequencing of variable regions of the 16S rRNA genes was used to characterize the microbial communities of 47 Kandalaksha Gulf sediment samples, collected at 10 cm below from the bottom surface. Pseudomonadota and Desulfobacterota were the most abundant phyla, which together comprised about a half of all prokaryotes. Determination of the dominant genus-level taxon proved impossible. The most represented chemoorganotrophic microorganisms were uncultured Sandaracinaceae (up to 10.8%) and Woeseia (up to 7.5%). Sulfate-reducing bacteria were important community components in the studied upper sediment layers, with uncultured groups SEEP-SRB1 (up to 7.0%) and Sva0081 (up to 5.9%) among the most abundant. In some samples, the genera Sulfurovum (up to 15.5%) and Thiohalophilus (up to 7.0%), involved in the oxidation of sulfur compounds, were important components of the community. Among the archaeal ASVs, the genus Nitrosopumilus, oxidizing ammonium to nitrite, exhibited the highest relative abundance (up to 6.9% of the total number of prokaryotes). Numerous sequences identified as the 16S rRNA gene fragments of chloroplasts were found in the samples, indicating that the rate of organic matter delivery to the upper sediment layers exceeded the rate of its degradation.