Sulfurihydrogenibium azorense, sp nov., a thermophilic hydrogen-oxidizing microaerophile from terrestrial hot springs in the Azores

Five hydrogen-oxidizing, thermophilic, strictly chemolithoautotrophic, microaerophilic strains, with similar (99-100%) 16S rRNA gene sequences were isolated from terrestrial hot springs at Furnas, Sao Miguel Island, Azores, Portugal. The strain, designated Az-Fu1(T), was characterized. The motile, 0.9-2.0 mum rods were Gram-negative and non-sporulating. The temperature growth range was from 50 to 73 degreesC; (optimum at 68 degreesC). The strains grew fastest in 0.1 % (w/v) NaCl and at pH 6, although growth was observed from pH 5.5 to 7.0. Az-Fu1(T) can use elemental sulfur, sulfite, thiosulfate, ferrous iron or hydrogen as electron donors, and oxygen (0.2-9.0%, v/v) as electron acceptor. Az-Fu1(T) is also able to grow anaerobically, with elemental sulfur, arsenate and ferric iron as electron acceptors. The Az-Fu1(T) G + C content was 33.6 mol%. Maximum-likelihood analysis of the 16S rRNA phylogeny placed the isolate in a distinct lineage within the Aquificales, closely related to Sulfurihydrogenibium subterraneum (2.0% distant). The 16S rRNA gene of Az-Fu1(T) is 7.7% different from that of Persephonella marina and 6.8% different from Hydrogenothermus marinus. Based on the phenotypic and phylogenetic characteristics presented here, it is proposed that Az-Fu1(T) belongs to the recently described genus Sulfurihydrogenibium. It is further proposed that Az-Fu1(T) represents a new species, Sulfurihydrogenibium azorense.