Sodium-Dependent Azotobacter chroococcum Strains Are Aeroadaptive, Microaerophilic, Nitrogen-Fixing Bacteria

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RESUMO

Na+ -dependent strains of Azotobacter chroococcum were observed to have very low reactivities with the H2O2 spot test for catalase. The cell extract of the representative Na+ -dependent strain 184 contained a catalase specific activity that was 10-to 600-fold lower than those found in Na+ -independent strains of A. chroococcum. Peroxidase and superoxide dismutase activities existed in all strains, although only certain Na+ -dependent strains contained a peroxidase reactive with p-phenylenediamine. The activities of catalase and peroxidase in the Na+ -dependent strain 184 were dependent on iron availability, which helped to explain the iron-dependent growth characteristic of this strain. The activities of these enzymes were not increased by subjecting the cells to increased aeration, nitrogen-fixing conditions, or paraquat. Strain 184 was found to be very sensitive to H2O2 or paraquat, even under iron-sufficient conditions, and was difficult to recover quantitatively on solid plating media. Strain 184 was more susceptible to H2O2 when grown under low-aeration, nitrogen-fixing conditions than when it was grown in the presence of NH4+. Low population densities of strain 184 grew in nitrogen-free medium under microaerophilic conditions, while more dense populations were able to fix nitrogen under aerobic conditions. Therefore, these bacteria appeared to be aeroadaptive, microaerophilic, nitrogen-fixing bacteria.

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