Natronincola ferrireducens sp. nov., and Natronincola peptidovorans sp. nov., new anaerobic alkaliphilic peptolytic iron-reducing bacteria isolated from soda lakes

Two novel strains of obligately alkaliphilic (pH 7.5–10.2, optimum pH 8.4–8.8) anaerobic spore-forming rod-shaped bacteria, Z-0511 and Z-7031, were isolated from enrichment cultures obtained from the iron-reducing (Lake Khadyn, Tyva) and cellulolytic (Lake Verkhnee Beloe, Buryatia) bacterial communities, respectively. The organisms ferment peptides and do not ferment proteins and amino acids, with the exception of histidine and glutamate utilized by strain Z-0511. The major fermentation products were acetate and propionate for strain Z-0511 and formate and acetate for strain Z-7031, respectively. Carbohydrates and fermentable organic acids could not serve as substrates, except for pyruvate in the case of strain Z-7031. Nitrogen and sulfur compounds were not utilized as electron acceptors by the strains grown on medium with yeast extract. Strain Z-0511 utilized fumarate, crotonate, and EDTA-Fe(III) as electron acceptors. Anthraquinone-2,6-disulfonate (quinone) and Mn(IV) were utilized by both strains, as well as amorphous ferric hydroxide (AFH), which was reduced to iron sesquioxides and magnetite. The presence of AFH stimulated growth; it enhanced the yield of the fermentation products and changed the quantitative ratios of these products. According to a phylogenetic analysis of the 16S rRNA gene sequences and the phenotypic characteristics of the new strains, they were classified as new species of the genus Natronincola, Natronincola ferrireducens sp. nov. Z-0511^T (= VKM B-2402, = DSM 18346) and Natronincola peptidovorans sp. nov. Z-7031^T (= VKM B-2503, = DSM 18979).