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Genetic and physiological analysis of the major OxyR-regulated katA from Xanthomonas campestris pv. phaseoli

Nopmanee Chauvatcharin^1,2,

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

Correspondence
Skorn Mongkolsuk
skorn{at}tubtim.cri.or.th

katA encodes the major catalase that accounts for 90 % of the total catalase activity present in Xanthomonas campestris pv. phaseoli. katA is located upstream of an ORF designated ankA encoding a cytoplasmic membrane protein homologous to eukaryotic ankyrin. Transcriptional analysis of katA and ankA identified two katA transcripts: a major monocistronic katA transcript and a minor bicistronic katA–ankA transcript. KatA expression was induced in the presence of various oxidants including H₂O₂, organic hydroperoxides and the superoxide-generating agent menadione, in an OxyR-dependent manner. Analysis of the katA promoter region showed a putative OxyR binding site located upstream of an Escherichia coli-like ⁷⁰ –35 region that is likely to be responsible for transcription activation in response to oxidant treatment. Gel mobility shift experiments confirmed that purified OxyR specifically binds to the katA promoter. A katA mutant was highly sensitive to H₂O₂ during both the exponential and stationary phases of growth. This phenotype could be complemented by functional katA, confirming the essential role of the gene in protecting X. campestris from H₂O₂ toxicity. Unexpectedly, inactivation of ankA also significantly reduced resistance to H₂O₂ and the phenotype could be complemented by plasmid-borne expression of ankA. Physiological analyses showed that katA plays an important role in, but is not solely responsible for, both the adaptive and menadione-induced cross-protective responses to H₂O₂ killing in X. campestris.

Present address: Center for Vectors and Vector-Borne Diseases, Mahidol University, Bangkok 10400, Thailand.

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