A novel facultatively anaerobic moderately thermophilic bacterium, strain B-154 T, was isolated from a terrestrial hot spring in the Baikal lake region (Russian Federation). Gram-negative, motile, spherical cells were present singly, in pairs, or aggregates, and reproduced by binary fission. The strain grew at 30-57 °C and within a pH range of 5.1-8.4 with the optimum at 50 °C and pH 6.8-7.1. Strain B-154 T was a chemoorganoheterotroph, growing on mono-, di- and polysaccharides (xylan, starch, galactan, galactomannan, glucomannan, xyloglucan, pullulan, arabinan, lichenan, beta-glucan, pachyman, locust bean gum, xanthan gum). It did not require sodium chloride or yeast extract for growth. Major cellular fatty acids were anteiso-C15:0, iso-C16:0 and iso-C14:0. The respiratory quinone was MK-7. The complete genome of strain B-154 T was 4.73 Mbp in size; its G + C content was 61%. According to the phylogenomic analysis strain B-154 T forms a separate family-level phylogenetic lineage. Moreover, together with Limisphaera ngatamarikiensis and "Pedosphaera parvula" this strain forms a separate order-level phylogenetic lineage within Verrucomicrobiae class. Hence, we propose a novel order, Limisphaerales ord. nov., with two families Limisphaeraceae fam. nov. and Fontisphaeraceae fam. nov., and a novel genus and species Fontisphaera persica gen. nov., sp. nov. with type strain B-154 T. Ecogenomic analysis showed that representatives of the Limisphaerales are widespread in various environments. Although some of them were detected in hot springs the majority of Limisphaerales (54% of the studied metagenome-assembled genomes) were found in marine habitats. This study allowed a better understanding of physiology and ecology of Verrucomicrobiota - a rather understudied bacterial phylum.
Keywords: Baikal lake; Fontisphaera; Fontisphaeraceae; Hydrolytic; Limisphaerales; Thermophilic.
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