Abstract
A novel anaerobic, thermophilic, alkalitolerant bacterium, strain 2204T, was isolated from a hot spring of the Baikal Lake region. The cells of strain 2204T were straight rods of variable length, Gram-positive with an S-layer, motile with one to two lateral flagella, and often formed aggregates of 315 cells. The isolate was shown to be an obligate anaerobe oxidizing CO and producing equimolar quantities of H2 and CO2 according to the equation CO+H2OCO2+H2. No organic substrates were used as energy sources. For lithotrophic growth on CO, 0·2 g acetate or yeast extract l1 was required but did not support growth in the absence of CO. Growth was observed in the temperature range 3768 °C, the optimum being 55 °C. The pH range for growth was 6·79·5, 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 2204T. Thus, isolate 2204T was found to be the first known moderately thermophilic and alkalitolerant H2-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 2204T 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 2204T (=DSM 17129T=VKM B-2283T=JCM 13258T).