New Anaerobic Iron-Cycling Bacteria Isolated from the Yessentukskoye Mineral Water Deposit

— Analysis of the composition of microbial communities of the Yessentukskoe mineral water deposit (YMWD) by molecular and classical microbiological methods revealed the presence of numerous uncultured bacteria of high taxonomic rank in the studied water-bearing horizons. Selective media with ferrihydrite (5Fe 2 O 3 ·9Н 2 O), magnetite (Fe 3 O 4 ), and siderite (FeCO 3 ) were used to obtain enrichment and pure cultures of iron-reducing microorganisms belonging to novel taxa in the phylum Actinobacterota (previously the uncultured order OPB41), order Deferribacterales , and the family Melioribacteraceae , as well as those related to the phylum Synergistota . Anaerobic iron-oxidizing bacteria belonged to the genera Ciceribacter and Bradyrhizobium. The results obtained expand our knowledge on biodiversity of the deep subsurface biosphere and reveal unexpected new metabolic features of previously characterized bacterial taxa.