Tourova, Tatjana P.

A moderately halophilic, obligately chemolithoautotrophic, sulfur-oxidizing bacterium, designated strain HRh1T, was obtained from mixed sediment samples from hypersaline chloride–sulfate lakes in the Kulunda Steppe, in south-western Siberia (Russia), using aerobic enrichment culture at 1 M NaCl with thiocyanate as substrate. Cells of the isolate were short, non-motile rods with a Gram-negative type of cell wall. The bacterium was an obligate aerobe capable of chemolithoautotrophic growth with thiocyanate and thiosulfate. With thiosulfate, it grew at NaCl concentrations of 0.2–3.0 M (optimum 0.5 M) and at pH 6.3–8.0 (optimum pH 7.3–7.5). During growth on thiocyanate, cyanate was identified as an intermediate. The dominant cellular fatty acids were C16 : 0and C18 : 1ω7. Phylogenetic analysis based on 16S rRNA gene sequencing placed the isolate in the classGammaproteobacteriaas an independent lineage, with an unclassified marine sulfur-oxidizing bacterium as the closest culturable relative (93 % sequence similarity). A singlecbbLgene (coding for the key enzyme of the Calvin–Benson cycle of autotrophic CO2assimilation) with relatively low similarity to any homologous genes found in chemolithoautotrophs was detected in strain HRh1T. On the basis of our phenotypic and phylogenetic analysis, the halophilic isolate is proposed to represent a new genus and novel species,Thiohalobacter thiocyanaticusgen. nov., sp. nov. The type strain ofThiohalobacter thiocyanaticusis HRh1T(=DSM 21152T=UNIQEM U249T).

A novel anaerobic, thermophilic, alkalitolerant bacterium, strain 2204T, was isolated from a hot spring of the Baikal Lake region. The cells of strain 2204Twere 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 H2and CO2according to the equation CO+H2O→CO2+H2. No organic substrates were used as energy sources. For lithotrophic growth on CO, 0·2 g acetate or yeast extract l−1was required but did not support growth in the absence of CO. Growth was observed in the temperature range 37–68 °C, the optimum being 55 °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 2204T. Thus, isolate 2204Twas found to be the first known moderately thermophilic and alkalitolerant H2-producing anaerobic carboxydotroph. The novel bacterium fell within the cluster of the familyPeptococcaceaewithin the low-G+C-content Gram-positive bacteria, where it formed a separate branch. On the basis of morphological, physiological and phylogenetic features, strain 2204Tshould be assigned to a novel genus and species, for which the nameThermincola carboxydiphilagen. nov., sp. nov. is proposed. The type strain is strain 2204T(=DSM 17129T=VKM B-2283T=JCM 13258T).