Activated sludge foaming: the true extent of actinomycete diversity

Isolates from activated sludge foam were provisionally assigned to the genera Gordona and Tsukamurella on the basis of colony morphology and pigmentation. Representatives of the first group were compared with marker strains of validly described species of Gordona by using Curie-point pyrolysis mass spectrometry. Most of the isolates fell into a number of taxa which were equated with groups of marker strains which corresponded to the known Gordona species. In a corresponding experiment the activated sludge isolates, which were provisionally labelled “Tsukamurella spumae” formed a group which was well separated from the marker strains of the genus. Representatives of the isolates were found to have chemical properties consistent with their classification in the genus Tsukamurella. 16S rDNA sequence data, when taken with previous DNA:DNA relatedness results, suggest that Tsukamurella paurometabola is heterogeneous. Similarly, the sequence data provide some evidence that “Tsukamurella spumae” may merit recognition as a novel species.