A new facultatively autotrophic hydrogen- and sulfur-oxidizing from an alkaline environment

An alkaliphilic bacterium, strain AHO 1, was isolated from an enrichment cu lture with hydrogen at pH 10 inoculated with a composite sample of sediment s from five highly alkaline soda lakes (Kenya). This bacterium is a gram-ne gative, nonmotile, rod-shaped, obligately aerobic, and facultatively autotr ophic hydrogen-oxidizing organism. It was able to oxidize reduced sulfur co mpounds to sulfate during heterotrophic growth. It utilized a wide range of organic compounds as carbon and energy sources and grew mixotrophically wi th hydrogen and acetate. With sulfur compounds, mixotrophic growth was obse rved only in acetate-limited continuous culture. The normal pH range for au totrophic growth with hydrogen was pH 8.0-10.25, with a pH optimum at 9-9.5 . Growth at pH values lower than 8.0 was extremely slow. Heterotrophic grow th with acetate was optimal at pH 10.0. The hydrogen-oxidizing activity of whole cells was maximal at pH 9.0 and still substantial up to pH 11. NAD-de pendent hydrogenase activity was found in the soluble fraction of the cell- free extract, but no methylene blue-dependent activity in either the solubl e or membrane fractions was observed. On the basis of its pH profile, the s oluble hydrogenase of strain AHO 1 was a typical pH-neutral enzyme. Phyloge netic analysis revealed that strain AHO 1 belongs to the alpha-3 subgroup o f the Proteobacteria with a closest relation to a recently described alkali philic aerobic bacteriochlorophyll a-containing bacterium "Roseinatronobact er thiooxidans".