Rikiya Takahashi

Isolation of Sphaerotilus natans-lysing microorganism from activated sludge

Abstract Sphaerotilus natans is thought to be a causative agent for bulking of activated sludge. Four microorganisms lysing S. natans were isolated from sewage activated sludge. One of the isolates, K-01, was investigated further. K-01 formed plaques 3–5 d after plating together with S. natans on PYG agar plates. The plaques enlarged gradually into surrounding S. natans cells and finally covered the entire surface of the plates. The isolate could not be filtered through a membrane filter with a pore size of 0.2 μm. Electron microscopic observation revealed that K-01 was long-rod shaped, Gram negative microorganism. K-01 could not be cultured on PYG agar medium without S. natans , but it was able to form small colonies on diluted bouillon agar medium without the host cell. K-01 strongly suppressed the growth of S. natans in liquid culture.