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Journal of Bacteriology, December 2000, p. 6845-6849, Vol. 182, No. 23
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

A Xanthomonas Alkyl Hydroperoxide Reductase Subunit C (ahpC) Mutant Showed an Altered Peroxide Stress Response and Complex Regulation of the Compensatory Response of Peroxide Detoxification Enzymes

Skorn Mongkolsuk,^1,2,* Wirongrong Whangsuk,^1,2 Paiboon Vattanaviboon,¹ Suvit Loprasert,¹ and Mayuree Fuangthong^1,

Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210,¹ and Department of Biotechnology, Faculty of Science, Mahidol University, Bangkok 10400,² Thailand

Received 12 June 2000/Accepted 13 September 2000

Alkyl hydroperoxide reductase subunit C (AhpC) is the catalytic subunit responsible for alkyl peroxide metabolism. A Xanthomonas ahpC mutant was constructed. The mutant had increased sensitivity to organic peroxide killing, but was unexpectedly hyperresistant to H₂O₂ killing. Analysis of peroxide detoxification enzymes in this mutant revealed differential alteration in catalase activities in that its bifunctional catalase-peroxidase enzyme and major monofunctional catalase (Kat1) increased severalfold, while levels of its third growth-phase-regulated catalase (KatE) did not change. The increase in catalase activities was a compensatory response to lack of AhpC, and the phenotype was complemented by expression of a functional ahpC gene. Regulation of the catalase compensatory response was complex. The Kat1 compensatory response increase in activity was mediated by OxyR, since it was abolished in an oxyR mutant. In contrast, the compensatory response increase in activity for the bifunctional catalase-peroxidase enzyme was mediated by an unknown regulator, independent of OxyR. Moreover, the mutation in ahpC appeared to convert OxyR from a reduced form to an oxidized form that activated genes in the OxyR regulon in uninduced cells. This complex regulation of the peroxide stress response in Xanthomonas differed from that in other bacteria.

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^* Corresponding author. Mailing address: Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand. Phone: (662) 574 0622, ext. 1402. Fax: (662) 574 2027. E-mail: skorn{at}tubtim.cri.or.th.

Present address: Section of Microbiology, Cornell University, Ithaca, NY 14853-8101.

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Journal of Bacteriology, December 2000, p. 6845-6849, Vol. 182, No. 23
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

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