Thermosinus carboxydivorans gen. nov., sp. nov., a new anaerobic, thermophilic, carbon-monoxide-oxidizing, hydrogenogenic bacterium from a hot pool of Yellowstone National Park

Abstract

A new anaerobic, thermophilic, facultatively carboxydotrophic bacterium, strain Nor1T, was isolated from a hot spring at Norris Basin, Yellowstone National Park. Cells of strain Nor1Twere curved motile rods with a length of 2·6–3 μm, a width of about 0·5 μm and lateral flagellation. The cell wall structure was of the Gram-negative type. Strain Nor1Twas thermophilic (temperature range for growth was 40–68 °C, with an optimum at 60 °C) and neutrophilic (pH range for growth was 6·5–7·6, with an optimum at 6·8–7·0). It grew chemolithotrophically on CO (generation time, 1·15 h), producing equimolar quantities of H2and CO2according to the equation CO+H2O→CO2+H2. During growth on CO in the presence of ferric citrate or amorphous ferric iron oxide, strain Nor1Treduced ferric iron but produced H2and CO2at a ratio close to 1 : 1, and growth stimulation was slight. Growth on CO in the presence of sodium selenite was accompanied by precipitation of elemental selenium. Elemental sulfur, thiosulfate, sulfate and nitrate did not stimulate growth of strain Nor1Ton CO and none of these chemicals was reduced. Strain Nor1Twas able to grow on glucose, sucrose, lactose, arabinose, maltose, fructose, xylose and pyruvate, but not on cellobiose, galactose, peptone, yeast extract, lactate, acetate, formate, ethanol, methanol or sodium citrate. During glucose fermentation, acetate, H2and CO2were produced. Thiosulfate was found to enhance the growth rate and cell yield of strain Nor1Twhen it was grown on glucose, sucrose or lactose; in this case, acetate, H2S and CO2were produced. In the presence of thiosulfate or ferric iron, strain Nor1Twas also able to grow on yeast extract. Lactate, acetate, formate and H2were not utilized either in the absence or in the presence of ferric iron, thiosulfate, sulfate, sulfite, elemental sulfur or nitrate. Growth was completely inhibited by penicillin, ampicillin, streptomycin, kanamycin and neomycin. The DNA G+C content of the strain was 51·7±1 mol%. Analysis of the 16S rRNA gene sequence revealed that strain Nor1Tbelongs to theBacillus–Clostridiumphylum of the Gram-positive bacteria. On the basis of the studied phenotypic and phylogenetic features, we propose that strain Nor1Tbe assigned to a new genus,Thermosinusgen. nov. The type species isThermosinus carboxydivoranssp. nov. (type strain, Nor1T=DSM 14886T=VKM B-2281T).