Affiliation:
1. Department of Microbiology, University of Alberta, Edmonton, Alberta, Canada
Abstract
Na
+
-dependent strains of
Azotobacter chroococcum
were observed to have very low reactivities with the H
2
O
2
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 H
2
O
2
or paraquat, even under iron-sufficient conditions, and was difficult to recover quantitatively on solid plating media. Strain 184 was more susceptible to H
2
O
2
when grown under low-aeration, nitrogen-fixing conditions than when it was grown in the presence of NH
4
+
. 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.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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