Polyphosphate-accumulating bacteria that were previously isolated from activated sludge and exhibited high phosphate removal activity were studied taxonomically and phylogenetically. These organisms were gram-positive, coccus-shaped, aerobic chemoorganotrophs that had a strictly respiratory type of metabolism in which oxygen was a terminal electron acceptor. They accumulated large amounts of polyphosphate under aerobic conditions. The major quinone was menaquinone MK-9(H4). The cell wall peptidoglycan contained LL-diaminopimelic acid. The guanine-plus-cytosine content of the DNA was 67.9 mol%. Our isolates were similar phenotypically and chemotaxonomically to Luteococcus japonicus, which was proposed recently as a new genus and species. However, our isolates differed from L. japonicus in cellular fatty acid composition and some other traits. A phylogenetic analysis based on 16S rRNA sequences showed that our isolate differ from the genus Luteococcus and other genera belonging to the high-G+C-content gram-positive group. Accordingly, we concluded that our strain NM-1T (T = type strain) should be assigned to a new genus and species, for which we propose the name Microlunatus phosphovorus.