Dethiosulfovibrio russensis sp nov., Dethiosulfovibrio marinus sp nov and Dethiosulfovibrio acidaminovorans sp nov., novel anaerobic, thiosulfate- and sulfur-reducing bacteria isolated from 'Thiodendron' sulfur mats in different saline environments

Four strains of strictly anaerobic, sulfur- and thiosulfate-reducing bacteria, SR12(T), SR13, SR15(T) and WS100(T), were isolated from 'Thiodendron' sulfur mats obtained from different saline environments. All isolates were motile, Gramnegative, non-spore-forming curved rods with pointed or rounded ends. The sizes of cells varied from 0.9 x 3-5 mum for strains SR12(T), SR13 and SR15(T) to 0.9 x 4-8 mum for strain WS100T. All strains could form long spiral filamentous cells up to 70-110 mum during the early stage of growth. All strains were motile by a tumbling movement and possessed lateral flagella arranged at the concave side of cells. Incomplete cross-septa were distinctive features of all strains. Growth occurred at temperatures of 10-40 degreesC with an optimum at 28 degreesC. The pH limits for growth were 5.5 to 8.0, with optimal growth at ph 6.5-7.0. All isolates were obligately anaerobic and slightly halophilic and grew in media containing 0.5-5 % NaCl with an optimum at 2 % NaCI. All strains were chemoorganoheterotrophic, having a fermentative type of metabolism and utilized proteins, peptides, amino acids and some organic acids, but not sugars, fatty acids or alcohols. Some organic substrates (isoleucine, valine, alanine, glutamate) were utilized only by strain SR12T in the presence of sulfur or thiosulfate. Fermentation of citrate yielded mainly acetate, CO2 and H-2. Sulfur and thiosulfate were reduced to hydrogen sulfide during the fermentation of organic substances, which increased cell yields and growth rates. Sulfate, sulfite, fumarate, nitrate, Fe2O3, MnO2, DMSO and elemental selenium were not used as electron accepters by these strains. The G+C contents of the DNA were 51 mol% for strains SR12(T), SR13 and SR15(T) and 52 mol% for strain WS100(T). Based on morphological, physiological and phylogenetic similarities, all four isolates could be assigned to three new species of the genus Dethiosulfovibrio, named Dethiosulfovibrio russensis (type strain DSM 12538(T)), Dethiosulfovikrio marinus (type strain DSM 12537(T)) and Dethiosulfovibrio acidaminovorans (type strain DSM 12590(T)).