Abstract
Two thermophilic, strictly chemolithoautotrophic, microaerophilic, hydrogen-oxidizing members of the Bacteria designated strain EX-H1(T) and strain EX-H2(T) were isolated from two separate deep-sea hydrothermal vent sites at 9degrees N 104degrees W in the Pacific Ocean and Guaymas Basin. The motile 2--4-microm-long rods were Gram-negative and non-sporulating. The temperature range for growth was between 55 and 80 degrees C for EX- H1(T) (optimum at 73 degrees C) and 55--75 degrees C for EX-H2(T) (optimum at 70 degrees C). Both strains grew fastest at 2.5% (w/v) NaCl and at pH 6, although growth was observed from pH 4.7 to pH 7.5. EX-H1(T) and EX-H2(T) were able to use elemental sulfur, thiosulfate or hydrogen as an electron donor, and oxygen (2--3%, v/v) or nitrate as an electron acceptor. EX-H1(T) was also able to use elemental sulfur as an electron acceptor. EX-H1(T) and EX-H2(T) further differed in their genomic G+C content (38.5 and 37.4 mol%, respectively) and 16S rRNA sequences (4% difference). Maximum-likelihood analysis of the 16S rRNA phylogeny placed both isolates within the Aquificales as a distinct lineage and showed them to be only about 85% similar to Aquifex pyrophilus. On the basis of phenotypic and phylogenetic characteristics, it is proposed that EX-H1(T) and EX-H2(T) belong to a new genus within the Aquificales, namely Persephonella gen. nov. It is further proposed that EX-H1(T) be named Persephonella marina sp. nov., the type species of the genus, and that EX-H2(T) be named Persephonella guaymasensis sp. nov., a second species in this genus.