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Journal of Bacteriology, March 2009, p. 1382-1392, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01550-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Oxygen-Limiting Conditions Enrich for Fimbriate Cells of Uropathogenic Proteus mirabilis and Escherichia coli{triangledown}

M. Chelsea Lane,1,{dagger} Xin Li,2,{dagger} Melanie M. Pearson,1,{dagger} Amy N. Simms,1,{dagger} and Harry L. T. Mobley1*

Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620,1 Rheumatology, Allergy, and Immunology Unit, Harvard Medical School, Charlestown Navy Yard, Charlestown, Massachusetts 021292

Received 31 October 2008/ Accepted 17 December 2008

MR/P fimbriae of uropathogenic Proteus mirabilis undergo invertible element-mediated phase variation whereby an individual bacterium switches between expressing fimbriae (phase ON) and not expressing fimbriae (phase OFF). Under different conditions, the percentage of fimbriate bacteria within a population varies and could be dictated by either selection (growth advantage of one phase) or signaling (preferentially converting one phase to the other in response to external signals). Expression of MR/P fimbriae increases in a cell-density dependent manner in vitro and in vivo. However, rather than the increased cell density itself, this increase in fimbrial expression is due to an enrichment of fimbriate bacteria under oxygen limitation resulting from increased cell density. Our data also indicate that the persistence of MR/P fimbriate bacteria under oxygen-limiting conditions is a result of both selection (of MR/P fimbrial phase variants) and signaling (via modulation of expression of the MrpI recombinase). Furthermore, the mrpJ transcriptional regulator encoded within the mrp operon contributes to phase switching. Type 1 fimbriae of Escherichia coli, which are likewise subject to phase variation via an invertible element, also increase in expression during reduced oxygenation. These findings provide evidence to support a mechanism for persistence of fimbriate bacteria under oxygen limitation, which is relevant to disease progression within the oxygen-restricted urinary tract.

* Corresponding author. Mailing address: Department of Microbiology and Immunology, University of Michigan Medical School, 5641 Medical Science Bldg. II, 1150 W. Medical Center Dr., Ann Arbor, MI 48109-0620. Phone: (734) 764-1466. Fax: (734) 763-7163. E-mail: hmobley{at}umich.edu

{triangledown} Published ahead of print on 29 December 2008.

{dagger} These authors contributed equally to this work.

Journal of Bacteriology, March 2009, p. 1382-1392, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01550-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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