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J Bacteriol, May 1998, p. 2636-2643, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Identification and Characterization of a New Organic Hydroperoxide Resistance (ohr) Gene with a Novel Pattern of Oxidative Stress Regulation from Xanthomonas campestris pv. phaseoli

Skorn Mongkolsuk,1,2,* Wipa Praituan,1,2 Suvit Loprasert,1 Mayuree Fuangthong,1 and Sangpen Chamnongpol2,dagger

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 December 1997/Accepted 9 March 1998

We have isolated a new organic hydroperoxide resistance (ohr) gene from Xanthomonas campestris pv. phaseoli. This was done by complementation of an Escherichia coli alkyl hydroperoxide reductase mutant with an organic hydroperoxide-hypersensitive phenotype. ohr encodes a 14.5-kDa protein. Its amino acid sequence shows high homology with several proteins of unknown function. An ohr mutant was subsequently constructed, and it showed increased sensitivity to both growth-inhibitory and killing concentrations of organic hydroperoxides but not to either H2O2 or superoxide generators. No alterations in sensitivity to other oxidants or stresses were observed in the mutant. ohr had interesting expression patterns in response to low concentrations of oxidants. It was highly induced by organic hydroperoxides, weakly induced by H2O2, and not induced at all by a superoxide generator. The novel regulation pattern of ohr suggests the existence of a second organic hydroperoxide-inducible system that differs from the global peroxide regulator system, OxyR. Expression of ohr in various bacteria tested conferred increased resistance to tert-butyl hydroperoxide killing, but this was not so for wild-type Xanthomonas strains. The organic hydroperoxide hypersensitivity of ohr mutants could be fully complemented by expression of ohr or a combination of ahpC and ahpF and could be partially complemented by expression ahpC alone. The data suggested that Ohr was a new type of organic hydroperoxide detoxification protein.

* Corresponding author. Mailing address: Laboratory of Biotechnology, Chulabhorn Research Institute, Lak Si, Bangkok 10210, Thailand. Phone: (662) 574-0622. Fax: (662) 574-2027. E-mail: scsmk{at}mucc.mahidol.ac.th.

dagger Present address: Laboratory of Genetics, Gent University, Gent B-9000, Belgium.

J Bacteriol, May 1998, p. 2636-2643, Vol. 180, No. 10
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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