Physiological importance of cytochrome c peroxidase in ethanologenic thermotolerant Zymomonas mobilis.

Zymomonas mobilis ZmCytC as a peroxidase bearing three heme c-binding motifs was investigated with ΔZmcytC constructed. The mutant exhibited filamentous shapes and reduction in growth under a shaking condition at a high temperature compared to the parental strain and became hypersensitive to exogenous H(2)O(2). Under the same condition, the mutation caused increased expression of genes for three other antioxidant enzymes. Peroxidase activity, which was detected in membrane fractions with ubiquinol-1 as a substrate but not with reduced horse heart cytochrome c, was almost abolished in ΔZmcytC. Peroxidase activity was also detected with NADH as a substrate, which was significantly inhibited by antimycin A. NADH oxidase activity of ΔZmcytC was found to be about 80% of that of the parental strain. The results suggest the involvement of ZmCytC in the aerobic respiratory chain via the cytochrome bc(1) complex in addition to the previously proposed direct interaction with ubiquinol and its contribution to protection against oxidative stress.