Thermincola carboxydiphila gen. nov., sp nov., a novel anaerobic, carboxydotrophic, hydrogenogenic bacterium from a hot spring of the Lake Baikal area

A novel anaerobic, thermophilic, alkalitolerant bacterium, strain 2204(T), was isolated from a hot spring of the Baikal Lake region. The cells of strain 2204(T) were straight rods of variable length, Gram-positive with an S-layer, motile with one to two lateral flagella, and often formed aggregates of 3-15 cells. The isolate was shown to be an obligate anaerobe oxidizing CO, and producing equimolar quantities of H-2 and CO2 according to the equation CO + H2O -> CO2 + H-2. No organic substrates were used as energy sources. For lithotrophic growth on CO, 0(.)2 g acetate or yeast extract l(-1) was required but did not support growth in the absence of CO. Growth was observed in the temperature range 37-68 degrees C, the optimum being 55 degrees C. The pH range for growth was 6(.)7-9(.)5, the optimum pH being 8(.)0. The generation time under optimal conditions was 1(.)3 h. The DNA G + C content was 45 mol%. Penicillin, erythromycin, streptomycin, rifampicin, vancomycin and tetracycline completely inhibited both growth and CO utilization by strain 2204(T). Thus, isolate 2204(T) was found to be the first known moderately thermophilic: and alkalitolerant H-2-producing anaerobic carboxydotroph. The novel bacterium fell within the cluster of the family Peptococcaceae within the low-G + C-content Gram-positive bacteria, where it formed a separate branch. On the basis of morphological, physiological and phylogenetic features, strain 2204(T) should be assigned to a novel genus and species, for which the name Thermincola carboxydiphila gen. nov., sp. nov. is proposed. The type strain is strain 2204(T) (=DSM 17129(T) =VKM B-2283(T)=JCM 13258(T)).