At one time, most of the species belonging to the genera Brevundimonas, Burkholderia, Ralstonia, and Acidovonax were members of the genus Pseudomonas.These organisms have been categorized into five unrelated rRNA homology groups through ribosomal ribonucleic acid (rRNA)-deoxyribonucleic acid (DNA) hybridization studies.belong to tRNA homology group III (along with genera Comamo- nas, Delftia, Hydrogenophaga spp.); Brevundimonas spp.Phenotypically, they are all aerobic, non-spore-forming, straight or slightly curved, slender, gram-negative bacilli with cells that range from 1 to 5 um long and 0.5 to 1 um wide.Members of these genera use a variety of carbohydrate, alcohol, and amino acid substrates as carbon and energy sources.Organisms in these genera have many similar phenotypic characteristics but are genetically distinct.make up rRNA homology group IV (and for completeness, Stenotrophomonas spp.All species except Burkholderia mallei are motile, having one or several polar flagella.belong to rRNA homology group 1: Burkholderia and Ralstonia spp.belong to rRNA homology group II; Acidovorax spp.Preudomonas spp.belong to group V).Although they are able to survive and