Kosenko Natalia Romanovna

A comprehensive study of prokaryotic communities (microbiomes) of bacterial mats and snottites from the karst cave Sheki-Kh’ekh was carried out for the first time, with comparison to cave soil-like bodies (SLBs) from the Muhammed-Kh’ekh cave and adjacent brown forest soil. The total abundance of bacterial cells in mats and snottites varied within a relatively narrow range, from 0.26 to 0.35 billion cells per mL, reaching maximum values in floating bacterial mats and minimum values in snottites. In soil-like bodies, the total bacterial abundance was 0.28 billion cells per g. Actinomycete mycelium was detected in all cave samples, with the highest values observed in floating bacterial mats and the lowest in shoreline bacterial mats.
Metabarcoding analysis (16S rRNA gene sequencing) revealed high taxonomic diversity of prokaryotic communities across the studied substrates. The greatest diversity was recorded in floating bacterial mats (25 phyla and 74 genera). In all cave substrates, the dominant phyla were Pseudomonadota and Bacillota, while Bacteroidota also dominated in floating bacterial mats. Lower relative abundances were observed for Actinomycetota, Verrucomicrobiota, Chloroflexota, Chlorobiota, and Thermodesulfobacteriota. Eleven bacterial phyla were shared between soil and floating bacterial mats: Pseudomonadota,Bacillota,Bacteroidota,Verrucomicrobiota,Chlorobiota,Chloroflexota,Actinomycetota,Acidobacteriota,Cyanobacteriota,Planctomycetota, and Armatimonadota, along with two candidate phyla, Sumerlaeota and Hydrogenedentes. Two archaeal phyla, Woesearchaeota and Nanoarchaeota, were detected in bacterial mats.
A total of 191 bacterial genera were identified across all studied substrates. Only 12 genera were common to bacterial mats and soil: Brevundimonas,Devosia, Flavobacterium,Luteolibacter, Paenibacillus,Paenisporosarcina,Pseudarthrobacter, Pseudomonas,Rhodanobacter,Sphingomonas, Sumerlaea, and Thermomonas. A distinctive feature of floating bacterial mat communities was the high representation of genera involved in sulfur cycling processes. Functional profiling revealed the predominance of sulfur- and iron-cycle-related functions in bacterial mats, whereas nitrogen-cycle-related functions and chemoheterotrophy prevailed in soil communities.
This study significantly expands current knowledge of the taxonomic composition of prokaryotic communities inhabiting bacterial mats and snottites of sulfidic caves in the Chechen Republic. The presence of bacterial genera involved in sulfur and iron transformation processes highlights their ecological significance. The results obtained on the diversity of prokaryotic communities in mats, snottites, and soil-like bodies are of interest for understanding ecosystem functioning and for the targeted search of strains with valuable biotechnological properties.