1995 Volume 41 Issue 2 Pages 99-117
The new strains of aerobic chemoorganotrophic rhodoquinone-containing bacteria previously isolated from activated sludge were studied from taxonomic and phylogenetic viewpoints. These strains were Gram- negative, nonmotile coccobacilli, had a strictly respiratory type of metabolism with oxygen or nitrate as the terminal acceptor, produced catalase and oxidase, and contained both ubiquinone-8 and rhodoquinone-8 as major quinones. DNA-DNA reassociation studies revealed that the new strains were highly related to each other at hybridization levels of more than 74%, suggesting the genetic coherency of the isolates as a single species. The 16S rRNA gene from one of the isolates, strain AS-P1, was amplified in vitro and sequenced directly. Sequence comparisons and a distance matrix tree analysis revealed that strain AS-P1 was most closely related to Comamonas testosteroni, a representative of the beta subclass of the Proteobacteria, but the level of sequence similarity between the two appeared to be low enough to warrant different generic allocations. The strains were differentiated from related organisms by a number of phenotypic and chemotaxonomic properties. Thus, we conclude that the isolates should be placed in a new genus and species of the beta subclass of the Proteobacteria, for which we propose the name Brachymonas denitrificans. Evolutionary relationships of rhodoquinone producers to bacterial species with various quinone classes were discussed on the basis of 16S rRNA sequence information.
