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Applied and Environmental Microbiology, July 2005, p. 3389-3398, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3389-3398.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

OusB, a Broad-Specificity ABC-Type Transporter from Erwinia chrysanthemi, Mediates Uptake of Glycine Betaine and Choline with a High Affinity

Gwénaëlle Choquet, Nathalie Jehan, Christine Pissavin, Carlos Blanco, and Mohamed Jebbar*

Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Ave. du Général Leclerc, 35042 Rennes, France

Received 10 November 2004/ Accepted 4 January 2005

The ability of Erwinia chrysanthemi to cope with environments of elevated osmolality is due in part to the transport and accumulation of osmoprotectants. In this study we have identified a high-affinity glycine betaine and choline transport system in E. chrysanthemi. By using a pool of Tn5-B21 ousA mutants, we isolated a mutant that could grow in the presence of a toxic analogue of glycine betaine (benzyl-glycine betaine) at high osmolalities. This mutant was impaired in its ability to transport all effective osmoprotectants in E. chrysanthemi. The DNA sequence of the regions flanking the transposon insertion site revealed three chromosomal genes (ousVWX) that encode components of an ABC-type transporter (OusB): OusV (ATPase), OusW (permease), and OusX (periplasmic binding protein). The OusB components showed a significant degree of sequence identity to components of ProU from Salmonella enterica serovar Typhimurium and Escherichia coli. OusB was found to restore the uptake of glycine betaine and choline through functional complementation of an E. coli mutant defective in both ProU and ProP osmoprotectant uptake systems. Competition experiments demonstrated that choline, dimethylsulfoniacetate, dimethylsulfoniopropionate, and ectoine were effective competitors for OusB-mediated betaine transport but that carnitine, pipecolate, and proline were not effective. In addition, the analysis of single and double mutants showed that OusA and OusB were the only osmoprotectant transporters operating in E. chrysanthemi.


* Corresponding author. Mailing address: Université de Rennes I, UMR-CNRS 6026, Département Osmorégulation chez les Bactéries, Campus de Beaulieu, Av. du Général Leclerc, 35042 Rennes, France. Phone: (33) 2-23-23-68-52. Fax: (33) 2-23-23-67-75. E-mail: mohamed.jebbar{at}univ-rennes1.fr.


Applied and Environmental Microbiology, July 2005, p. 3389-3398, Vol. 71, No. 7
0099-2240/05/$08.00+0     doi:10.1128/AEM.71.7.3389-3398.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.




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