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J. Bacteriol. doi:10.1128/JB.00763-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Characterization of the osmoprotectant transporter OpuC from Pseudomonas syringae and demonstration that CBS domains are required for its osmoregulatory function

Department of Plant Pathology, Iowa State University, Ames, IA 50011-3211, USA

^* To whom correspondence should be addressed. Email: gbeattie{at}iastate.edu.

	Abstract

The plant pathogen Pseudomonas syringae may cope with osmotic stress on plants, in part, by importing osmoprotective compounds. In this study, we found that P. syringae pv. tomato (Pst) strain DC3000 was distinct from most bacterial species in deriving greater osmoprotection from exogenous choline than from glycine betaine. This superior osmoprotection was correlated with a higher capacity for uptake of choline than glycine betaine. Of four putative osmoregulatory ABC transporters in DC3000, one, designated OpuC, functioned as the primary or sole transporter for glycine betaine and as one of multiple transporters for choline under high osmolarity. Surprisingly, the homolog of the well-characterized ProU transporter from Escherichia coli and Salmonella typhimurium did not function in osmoprotection. The Pst OpuC transporter was more closely related to the Bacillus subtilis and Listeria monocytogenes OpuC transporters than to known osmoprotectant transporters in Gram-negative bacteria based on sequence similarity and genetic arrangement. The Pst OpuC transporter had a high affinity for glycine betaine, a low affinity for choline, and a broad substrate specificity that included acetylcholine, carnitine and proline betaine. Tandem cystathionine--synthase (CBS) domains in the ATP-binding component of OpuC were required for transporter function. The presence of these CBS domains was correlated with osmoregulatory function among the putative transporters examined in DC3000, and was found to be predictive of functional osmoregulatory transporters in other pseudomonads. These results provide the first functional evaluation of an osmoprotectant transporter in a Pseudomonas species and demonstrate the usefulness of the CBS domains as predictors of osmoregulatory activity.

This article has been cited by other articles:

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• Goldberg, J. B., Hancock, R. E. W., Parales, R. E., Loper, J., Cornelis, P. (2008). Pseudomonas 2007. J. Bacteriol. 190: 2649-2662 [Full Text]