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Journal of Bacteriology, March 2009, p. 1463-1471, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01583-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Functional Differences of Two Distinct Catalases in Mesorhizobium loti MAFF303099 under Free-Living and Symbiotic Conditions{triangledown}

Masaki Hanyu,1,2 Hanae Fujimoto,1 Kouhei Tejima,1 and Kazuhiko Saeki1*

Department of Biological Sciences, Faculty of Science, Nara Women's University, Nara 630-8506,1 Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan2

Received 8 November 2008/ Accepted 4 December 2008

Protection against reactive oxygen species (ROS) is important for legume-nodulating rhizobia during the establishment and maintenance of symbiosis, as well as under free-living conditions, because legume hosts might assail incoming microbes with ROS and because nitrogenase is extremely sensitive to ROS. We generated mutants of two potential catalase genes in Mesorhizobium loti MAFF303099 to investigate their physiological significance. Biochemical results indicated that genes with the locus tags mlr2101 and mlr6940 encoded a monofunctional catalase and a bifunctional catalase-peroxidase, respectively, that were named katE and katG. Under free-living conditions, the katG mutant demonstrated an extended generation time and elevated sensitivity to exogenous H2O2, whereas the katE mutant exhibited no generation time extension and only a slight increase in sensitivity to exogenous H2O2. However, the katE mutant showed a marked decrease in its survival rate during the stationary phase. With regard to symbiotic capacities with Lotus japonicus, the katG mutant was indistinguishable from the wild type; nevertheless, the mutants with disrupted katE formed nodules with decreased nitrogen fixation capacities (about 50 to 60%) compared to those formed by the wild type. These mutant phenotypes agreed with the expression profiles showing that transcription of katG, but not katE, was high during the exponential growth phase and that transcription levels of katE versus sigA were elevated during stationary phase and were approximately fourfold higher in bacteroids than mid-exponential-phase cells. Our results revealed functional separation of the two catalases, as well as the importance of KatE under conditions of strong growth limitation.

* Corresponding author. Mailing address: Department of Biological Sciences, Faculty of Science, Nara Women's University, Nara 630-8506, Japan. Phone and fax: 81-742-20-3028. E-mail: ksaeki{at}cc.nara-wu.ac.jp

{triangledown} Published ahead of print on 12 December 2008.

Journal of Bacteriology, March 2009, p. 1463-1471, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01583-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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