Proposal to reject the genus Hydrogenomonas: Taxonomic implications

Abstract

Fifty- six strains of "hydrogen bacteria and relate dnonaut o t r op hi c ba ct e r ia, including nearly all existing named Hydroge- nomonas spp., have been compared. It is pro- posed that the genus Hydrogenomonas should be rejected, since its type species EJ. panto- tropha, appears to be a nomen dubium; and that the various species of "hydrogen bacte- ria" should be assigned to other genera, not specifically characterized by the ability to grow autotrophically with H2. The two species of hydrogen bacteria most frequently isolated by enrichment show a peritrichous or degenerate peritrichous fla- gellar arrangement; one is nonpigmented, the other produces yellow (carotenoid) cellular pigments. Of the various possible generic assignments for these two species, assign- ment to the genus Alcaligenes is proposed. The nonpigmented species, previously named Hydrogenomonas eutropha, but never legiti- mately described, is here described as A. eutrophus. The yellow species which includes both facultatively autotrophic and nonautotro- phic strains, is described as a new species, - A. paradoxus. The Gram-negative, coccoid hydrogen bacterium, formerly known as Mi-crococcus denitrificans, is placed in a new genus, Paracoccus. The polarly flagellated species of hydrogen bacteria, including the previously named species Hydrogenomonas facilis, H. flava, H. ruhlandii andwPseudo- monas saccharophila, are all assigned to the genus Pseudomonas.