Calorithrix insularis gen. nov., sp nov., a novel representative of the phylum Calditrichaeota

A moderately thermophilic, anaerobic bacterium designated as strain KRT was isolated from a shallow-water submarine hydrothermal vent (Kunashir Island, Southern Kurils, Russia). Cells of strain KRT were thin (0.2-0.3 mu m), flexible, motile, Gram-stain-negative rods of variable length. Optimal growth conditions were pH 6.6, 55 degrees C and 1-3% (w/v) NaCl. Strain KRT was able to ferment a wide range of proteinaceous substrates, pyruvate, and mono-, di- and polysaccharides. The best growth occurred with proteinaceous compounds. Nitrate significantly stimulated the growth on proteinaceous substrates decreasing H-2 formation, ammonium being the main product of nitrate reduction. Strain KRT did not need the presence of a reducing agent in the medium and tolerated the presence of oxygen in the gas phase up to 3% (v/v). In the presence of nitrate, aerotolerance of isolate KRT was enhanced up to 6-8% O-2 (v/v). Strain KRT was able to grow chemolithoheterotrophically, oxidizing H-2 and reducing nitrate to ammonium. Yeast extract (0.05 g l(-1)) was required for growth. The G+C content of the genomic DNA of strain KRT was 47.3 mol%. 16S rRNA gene sequence analysis placed isolate KRT in the phylum Calditrichaeota where it represented a novel species of a new genus, for which the name Calorithrix insularis gen. nov., sp. nov. is proposed. The type strain of Calorithrix insularis is KRT (=DSM 101605(T) =VKM B-3022(T)).