Abstract
A novel thermophilic hydrogen-oxidizing bacterium, Hydrogenophilus hirschii Yel5a(T) (=DSM 11420(T)=JCM 10831(T)) has been isolated from the Angel Terrace Spring, Yellowstone National Park. The isolate was rod-shaped (1.0--1.5 x 0.8 microm) with a polarly inserted flagellum. Cells grew chemolithoautotrophically under an atmosphere of H(2) and CO(2) (80:20) in the presence of low concentrations of O(2) (optimum 2.5%). Organotrophic growth occurred on complex organic substrates such as yeast extract and peptone and on organic acids. Carbohydrates and amino acids were not utilized. The strain grew between 50 and 67 degrees C; optimal growth occurred at a temperature of 63 degrees C. The pH optimum was 6.5. NaCl inhibited growth at concentrations higher than 1.5%. The major respiratory lipoquinone was ubiquinone-8. Analysis of fatty acids of Yel5a(T) revealed a straight-chain saturated C(16:0) as the major component followed by cyclo C(17:0) and cyclo C(19:0). The G+C content of total DNA was 61 mol%. Phylogenetic analysis placed the strain in the beta-proteobacteria. The 16S rDNA sequence of strain Yel5a(T) was related to that of Hydrogenophilus thermoluteolus. To our knowledge, Hydrogenophilus hirschii is the most thermophilic micro-organism found within the proteobacteria that grows in the temperature range 50--68 degrees C.