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L-Rhamnose Transport Is Sugar Kinase (RhaK) Dependent in Rhizobium leguminosarum bv. trifolii

Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada

Received 29 June 2007/ Accepted 11 September 2007

Strains of Rhizobium leguminosarum which are unable to catabolize L-rhamnose, a methyl-pentose sugar, are compromised in the ability to compete for nodule occupancy versus wild-type strains. Previous characterization of the 11-kb region necessary for the utilization of rhamnose identified a locus carrying catabolic genes and genes encoding the components of an ABC transporter. Genetic evidence suggested that the putative kinase RhaK carried out the first step in the catabolism of rhamnose. Characterization of this kinase led to the observation that strains carrying rhamnose kinase mutations were unable to transport rhamnose into the cell. The absence of a functional rhamnose kinase did not stop the transcription and translation of the ABC transporter components. By developing an in vitro assay for RhaK activity, we have been able to show that (i) RhaK activity is consistent with RhaK phosphorylating rhamnose and (ii) biochemical activity of RhaK is necessary for rhamnose transport.

Published ahead of print on 21 September 2007.

This article has been cited by other articles:

• Richardson, J. S., Carpena, X., Switala, J., Perez-Luque, R., Donald, L. J., Loewen, P. C., Oresnik, I. J. (2008). RhaU of Rhizobium leguminosarum Is a Rhamnose Mutarotase. J. Bacteriol. 190: 2903-2910 [Abstract] [Full Text]