Catalase and superoxide dismutase activity in ammonia-oxidising bacteria
A range of ammonia-oxidising bacteria (AOB) was tested for the presence of the oxidative stress enzymes catalase and superoxide dismutase (SOD). All AOB possessed both activities, but overall activity and regulation were in several ways different among the strains. Nitrosomonas europaea contained very high specific activities of catalase compared to the other nitrifiers. Only one catalase isozyme, expressed at a constant specific activity per cell during growth in batch culture, was detectable in N. europaea by native PAGE analysis. In contrast, Nitrosospira multiformis possessed four catalase isozymes whose expression was strongly regulated by growth phase in batch culture. SOD expression patterns in the strains generally followed those of catalase, although changes of the SOD isozyme profiles were not apparent in batch culture. Growth of N. europaea on the surface of membrane filters (microcolony and biofilm formation) resulted in altered proportions of catalase and SOD specific activities, indicating regulation by cell density. This report represents the first description of different isozyme composition and of growth phase-dependent regulation of catalase and SOD enzyme production in AOB.