A novel Gram-negative coccus/coccobacillus, strain Ben 114T, growing in tetrads, clusters or aggregates, was isolated from activated sludge by micromanipulation. 16S rRNA gene sequence analysis revealed that it belonged to the ‘
Alphaproteobacteria’, with no close relatives among cultured bacterial isolates. On the basis of phylogenetic data, this organism is considered to belong to a new genus, Defluvicoccus, represented by the species Defluvicoccus vanussp. nov., a name chosen because of the distinctive staining properties of this organism; only the cell wall stained strongly with a wide range of stains, giving the cell a hollow and empty appearance. No intracellular polyphosphate granules could be detected after staining, but poly- β-hydroxyalkanoate inclusions were detected using Nile blue A staining. Because of its taxonomic distance from its closest relatives among the ‘ Alphaproteobacteria’, namely members of the genera Azospirillum, Phaeospirillum, Rhodospirillum, Rhodocista, Magnetospirillumand Rhodospira, D. vanusis considered to represent a new phylogenetic lineage within subgroup 1 of the ‘ Alphaproteobacteria’, the D. vanussubgroup. The type strain is Ben 114T (=NCIMB 13612T=CIP 107350T).