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Appl. Environ. Microbiol. doi:10.1128/AEM.01508-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Identification of Campylobacter jejuni genes contributing to acid adaptation by transcriptional profiling and genome-wide mutagenesis

Ottawa Institute of Systems Biology, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, 451 Smyth road, Ottawa, K1H 8M5, ON, Canada; Department of Veterinary Pathobiology, Oklahoma State University, Stillwater, OK, 74078, USA

^* To whom correspondence should be addressed. Email: astintzi{at}uottawa.ca.

	Abstract

In order to cause disease, the food- and water-borne pathogen Campylobacter jejuni must face the extreme acidity of the host stomach as well as cope with pH fluctuations in the intestine. In the present study, C. jejuni NCTC 11168 was grown under mild acidic conditions mimicking those encountered in the intestine. The resulting transcriptional profiles revealed how this bacterium fine-tunes gene expression in response to acid stress. This adaptation involves differential expression of respiratory pathways, induction of genes for phosphate transport and repression of energy generation and intermediary metabolism genes. We also generated and screened a transposon-based mutant library to identify genes required for wild-type levels of growth under mild acidic conditions. This screen highlighted the important role played by cell surface components (flagella, outer membrane, capsular polysaccharides, lipooligosaccharides) in the acid stress response of C. jejuni. Our data also revealed that limited correlation exists between genes required for growth under acidic conditions and genes differentially expressed in response to acid. To gain a comprehensive picture of the acid stress response of C. jejuni, we merged transcriptional profiles obtained from acid-adapted cells and cells subjected to acid shock. Genes encoding the transcriptional regulator PerR and putative oxidoreductase subunits Cj0414 and Cj0415 were among the few up-regulated under both acid stress conditions. As a Cj0415 mutant was acid-sensitive, it is likely that these genes are crucial to the acid stress response of C. jejuni, and consequently important for host colonization.

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