An isolate of a Gram-positive bacterium, designated strain Ben 106T, was obtained in pure culture by micromanipulation of a biomass sample obtained from a laboratory-scale sequencing batch reactor. This isolate grew axenically as cocci or clusters of cocci arranged in regular tetrads and was morphologically similar to the dominant organism observed in the biomass. This morphology resembled that of some Gram-positive and -negative bacteria and the so-called 'G-bacteria' commonly seen in activated sludge samples. Strain Ben 106T is a non-motile, facultative anaerobe. It is oxidase-negative, catalase-positive and is capable of reducing nitrate. This organism can grow between 20 and 37 degrees C, with an optimum temperature of 25 degrees C. The pH range for growth is between 6.0 and 9.0, with an optimum pH of 7.5. The isolate stained positively for intracellular polyphosphate granules. The diagnostic diamino acid of the peptidoglycan is LL-diaminopimelic acid (LL-A2pm) with a glycine moiety at position 1 of the peptide subunit, which characterizes the presence of a rare peptidoglycan (type A3-gamma'). Two menaquinones, MK-9(H4) and MK-7(H4), are present and the main cellular fatty acid is 12-methyltetradecanoic acid. The G + C content is 74 mol%. From phenotypic characteristics and 16S rDNA sequence analysis, the isolate differed sufficiently from its closest phylogenetic relatives, namely Propionibacterium propionicum, Propioniferax innocua, Friedmanniella antarctica, Luteococcus japonicus and Microlunatus phosphovorus in the A1 subdivision of the Gram-positive bacteria (i.e. Firmicutes with a high G + C content), suborder Propionibacterineae, to be placed in a new genus, Tessaracoccus, as Tessaracoccus bendigoensis gen. nov., sp. nov. The type strain is Ben 106T (= ACM 5119T).