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Journal of Bacteriology, April 2009, p. 2296-2306, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01430-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

A DNase Encoded by Integrated Element CJIE1 Inhibits Natural Transformation of Campylobacter jejuni{triangledown} ,{dagger}

Esther J. Gaasbeek,1,2 Jaap A. Wagenaar,1,2,4 Magalie R. Guilhabert,3,{ddagger} Marc M. S. M. Wösten,2,4 Jos P. M. van Putten,2,4 Linda van der Graaf-van Bloois,1 Craig T. Parker,3 and Fimme J. van der Wal1,4*

Department of Bacteriology and TSEs, Central Veterinary Institute of Wageningen UR, Lelystad, The Netherlands,1 Department of Infectious Diseases and Immunology, Utrecht University, Yalelaan 1, 3584 CL Utrecht, The Netherlands,2 Produce Safety and Microbiology Research Unit, Agricultural Research Service, U.S. Department of Agriculture, 800 Buchanan Street, Albany, California 94710,3 WHO/OIE Collaborating Centre/Reference Laboratory for Campylobacter, The Netherlands4

Received 13 October 2008/ Accepted 8 January 2009

The species Campylobacter jejuni is considered naturally competent for DNA uptake and displays strong genetic diversity. Nevertheless, nonnaturally transformable strains and several relatively stable clonal lineages exist. In the present study, the molecular mechanism responsible for the nonnatural transformability of a subset of C. jejuni strains was investigated. Comparative genome hybridization indicated that C. jejuni Mu-like prophage integrated element 1 (CJIE1) was more abundant in nonnaturally transformable C. jejuni strains than in naturally transformable strains. Analysis of CJIE1 indicated the presence of dns (CJE0256), which is annotated as a gene encoding an extracellular DNase. DNase assays using a defined dns mutant and a dns-negative strain expressing Dns from a plasmid indicated that Dns is an endogenous DNase. The DNA-hydrolyzing activity directly correlated with the natural transformability of the knockout mutant and the dns-negative strain expressing Dns from a plasmid. Analysis of a broader set of strains indicated that the majority of nonnaturally transformable strains expressed DNase activity, while all naturally competent strains lacked this activity. The inhibition of natural transformation in C. jejuni via endogenous DNase activity may contribute to the formation of stable lineages in the C. jejuni population.

* Corresponding author. Mailing address: Central Veterinary Institute of Wageningen UR, Department of Bacteriology and TSEs, P.O. Box 65, 8200 AB Lelystad, The Netherlands. Phone: (31) 320 238395. Fax: (31) 320 238961. E-mail: Fimme.vanderWal{at}wur.nl

{triangledown} Published ahead of print on 16 January 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

{ddagger} Present address: AgraQuest, 1540 Drew Avenue, Davis, CA 95618.

Journal of Bacteriology, April 2009, p. 2296-2306, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01430-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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