In situ characterization of substrate uptake by Microthrix parvicella using microautoradiography

Microthrix parvicella is a filamentous microorganism responsible for bulking and foaming problems in many activated sludge treatment plants. The problems have increased with the introduction of nutrient removal in many countries, and presently, there is no reliable control strategy for M. parvicella. Little is known about the physiology of M. parvicella, and conflicting data exist about its preferred organic substrates, and whether it is able to be physiologically active under anaerobic and anoxic conditions. In this study, the ability of M. parvicella to take up various radioactively labeled organic compounds was investigated in situ at three nutrient removal plants using a microautoradiographic technique. Of 12 compounds tested under aerobic conditions only the long chain fatty acids (LCFA), oleic acid and palmitic acid, and to some extent a lipid, trioleic acid, were assimilated. None of the simple substrates such as acetate, propionate, butyrate, glucose, ethanol, glycine and leucine were taken up. Furthermore, the uptake of oleic acid was compared under anaerobic, anoxic and aerobic conditions, and it was demonstrated that in addition to aerobic conditions M. parvicella was also able to take up oleic acid under anaerobic and anoxic conditions. No difference in substrate uptake pattern for M. parvicella was found among the tested activated sludge plants. The results strongly indicate that a better control strategy against M. parvicella must rely on a better understanding of presence and availability of triglycerides and LCFA, and an improved knowledge of the physiology of M. parvicella under anaerobic and anoxic conditions.