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Journal of Bacteriology, December 2004, p. 7874-7880, Vol. 186, No. 23
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.23.7874-7880.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

KatG Is the Primary Detoxifier of Hydrogen Peroxide Produced by Aerobic Metabolism in Bradyrhizobium japonicum

Heather R. Panek and Mark R. O'Brian^*

Department of Biochemistry and Witebsky Center for Microbial Pathogenesis and Immunology, State University of New York at Buffalo, Buffalo, New York

Received 18 June 2004/ Accepted 2 September 2004

Bacteria are exposed to reactive oxygen species from the environment and from those generated by aerobic metabolism. Catalases are heme proteins that detoxify H₂O₂, and many bacteria contain more than one catalase enzyme. Also, the nonheme peroxidase alkyl hydroperoxide reductase (Ahp) is the major scavenger of endogenous H₂O₂ in Escherichia coli. Here, we show that aerobically grown Bradyrhizobium japonicum cells express a single catalase activity. Four genes encoding putative catalases in the B. japonicum genome were identified, including a katG homolog encoding a catalase-peroxidase. Deletion of the katG gene resulted in loss of catalase activity in cell extracts and of exogenous H₂O₂ consumption by whole cells. The katG strain had a severe aerobic growth phenotype but showed improved growth in the absence of O₂. By contrast, a B. japonicum ahpCD mutant grew well aerobically and consumed H₂O₂ at wild-type rates. A heme-deficient hemA mutant expressed about one-third of the KatG activity as the wild type but grew well aerobically and scavenged low concentrations of exogenous H₂O₂. However, cells of the hemA strain were deficient in consumption of high concentrations of H₂O₂ and were very sensitive to killing by short exposure to H₂O₂. In addition, KatG activity did not decrease as a result of mutation of the gene encoding the transcriptional activator OxyR. We conclude that aerobic metabolism produces toxic levels of H₂O₂ in B. japonicum, which is detoxified primarily by KatG. Furthermore, the katG level sufficient for detoxification does not require OxyR.

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* Corresponding author. Mailing address: Department of Biochemistry, 140 Farber Hall, State University of New York at Buffalo, Buffalo, NY 14214. Phone: (716) 829-3200. Fax: (716) 829-2725. E-mail: mrobrian{at}buffalo.edu.

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Journal of Bacteriology, December 2004, p. 7874-7880, Vol. 186, No. 23
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.23.7874-7880.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

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