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Journal of Bacteriology, September 2006, p. 6308-6317, Vol. 188, No. 17
0021-9193/06/$08.00+0     doi:10.1128/JB.00585-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

Proline Betaine Uptake in Sinorhizobium meliloti: Characterization of Prb, an Opp-Like ABC Transporter Regulated by both Proline Betaine and Salinity Stress

Geneviève Alloing,^* Isabelle Travers, Brice Sagot, Daniel Le Rudulier, and Laurence Dupont

Unité Interactions Plantes-Microorganismes et Santé Végétale, UMR6192 CNRS-INRA-Université de Nice Sophia Antipolis, Centre INRA Agrobiotech, Sophia Antipolis, France

Received 25 April 2006/ Accepted 13 June 2006

Sinorhizobium meliloti uses proline betaine (PB) as an osmoprotectant when osmotically stressed and as an energy source in low-osmolarity environments. To fulfill this dual function, two separate PB transporters, BetS and Hut, that contribute to PB uptake at high and low osmolarity, respectively, have been previously identified. Here, we characterized a novel transport system that mediates the uptake of PB at both high and low osmolarities. Sequence analysis of Tn5-luxAB chromosomal insertions from several PB-inducible mutants has revealed the presence of a four-gene locus encoding the components of an ABC transporter, Prb, which belongs to the oligopeptide permease (Opp) family. Surprisingly, prb mutants were impaired in their ability to transport PB, and oligopeptides were not shown to be competitors for PB uptake. Further analysis of Prb specificity has shown its ability to take up other quaternary ammonium compounds such as choline and, to a lesser extent, glycine betaine. Interestingly, salt stress and PB were found to control prb expression in a positive and synergistic way and to increase Prb transport activity. At low osmolarity, Prb is largely implicated in PB uptake by stationary-phase cells, likely to provide PB as a source of carbon and nitrogen. Furthermore, at high osmolarity, the analysis of prb and betS single and double mutants demonstrated that Prb, together with BetS, is a key system for protection by PB.

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* Corresponding author. Mailing address: Unité Interactions Plantes-Microorganismes et Santé Végétale, UMR6192 CNRS-INRA-Université de Nice Sophia Antipolis, Centre INRA Agrobiotech, 400 Route des Chappes, BP167, 06903 Sophia Antipolis Cédex, France. Phone: (33) 492 386 632. Fax: (33) 492 386 630. E-mail: alloing{at}unice.fr.

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Journal of Bacteriology, September 2006, p. 6308-6317, Vol. 188, No. 17
0021-9193/06/$08.00+0     doi:10.1128/JB.00585-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

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