Taxonomic and Functional Analysis of Metagenome-Assembled Genomes from Saline Lakes of the Barguzin Depression (Baikal Rift Zone)

Abstract— This work presents the first analysis of metagenome-assembled genomes (MAGs) of lake bottom sediments of the Barguzin Depression (Baikal Rift Zone). For soda–saline Lake Gudzhirganskoe, altogether 16 prokaryotic MAGs were distributed across six phyla: Bacillota, Bacteroidota, Deinococcota, Desulfobacterota, Gemmatimonadota, and Pseudomonadota. In soda Lake Nukhe-Nur, 21 prokaryotic MAGs represented six bacterial phyla: Bacteroidota, Bipolaricaulota, Chloroflexota, Deinococcota, Desulfobacterota, and Pseudomonadota, as well as three archaeal phyla: Aenigmatarchaeota, Halobacteriota, and Thermoplasmatota. A significant share of these MAGs (over 76% on the genus level) represented new taxa that could not be assigned to known genera. Functional profiling of the 37 MAGs revealed a range of marker genes involved in the biogeochemical cycles of carbon, nitrogen, and sulfur. It was shown that the microbial communities of the studied lakes had distinct features in terms of their functional potential. In particular, the processes with the greatest potential for carbon fixation: the Calvin cycle, the Wood–Ljungdahl pathway, and the reductive tricarboxylic acid cycle (rTCA), were most prevalent in Lake Nukhe-Nur, whereas the crucial stage of energy metabolism in Lake Gudzhirganskoe was oxidative phosphorylation. Only a few MAGs possessed marker genes of nitrogen fixation and dissimilatory nitrate reduction to ammonia (DNRA). In the sulfur cycle, the key actors were members of Desulfobacterota and Gammaproteobacteria, which participated in dissimilatory sulfate reduction and oxidation of sulfur compounds.