Isolation and characterization of a Gram-positive polyphosphate-accumulating bacterium.

A Gram-positive polyphosphate-accumulating bacterium was isolated from phosphate-removal activated sludge using pyruvate-supplemented agar plates. The isolate was oval or coccobacilli (0.4-0.7 x 0.5-1.0 mm) that occurred singly, in pairs or irregular clumps. Polyphosphate granules in the cells were observed by toluidine blue staining. The pure culture of the isolate rapidly took up phosphate (9.2 mg-P/g-dry weight) in the 3-h aerobic incubation without organic substrates, after anaerobic incubation with organic substrates containing casamino acids. When acetate was the sole carbon source in the anaerobic incubation, the isolate did not remove phosphate. These physiological features of the isolate were similar to those of Microlunatus phosphovorus. However, unlike M. phosphovorus the P-removal ability of the isolate was relatively low and was not accelerated by repeating the anaerobic/aerobic incubation cycles. Phylogenetic analysis and comparison of several characteristics showed that the isolate was identified as Tetrasphaera elongata which was recently proposed as a new polyphosphate-accumulating species isolated from activated sludge. As the isolate contained menaquinone (MK)-8(H(4)) as the predominant isoprenoid ubiquinone, it may be significantly responsible for phosphate removal, because MK-8(H(4)) has reportedly been found in fairly high proportions in many phosphate-removing activated sludges.