Susceptibility to hydrogen peroxide and catalase activity of root nodule bacteria

The root nodule bacteria (free-living cells) tested had higher susceptibili ty to hydrogen peroxide (H2O2) than the other genera of aerobic or facultat ive anaerobic bacteria tested. The catalase activities tended to have a pos itive correlation with H2O2 resistance among all bacteria tested. Addition of a catalase inhibitor such as 3-amino-1,2,4-triazole increased the suscep tibility to H2O2. These results suggest that the:lower catalase activity br ings about the higher susceptibility of root nodule bacteria to H2O2. Root nodule bacteria seemed to have two or three catalase isozymes during growth and their catalase activities were higher in log phase than in stationary phase, contrary to other genera of bacteria tested.