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Journal of Bacteriology, August 2009, p. 5057-5067, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00252-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

An Alternative Succinate (2-Oxoglutarate) Transport System in Rhizobium tropici Is Induced in Nodules of Phaseolus vulgaris{triangledown} ,{dagger}

Silvia Batista,1* Eduardo J. Patriarca,2 Rosarita Tatè,2 Gloria Martínez-Drets,1 and Paul R. Gill1,3

Unidad de Microbiología Molecular, Instituto de Investigaciones Biológicas Clemente Estable, Av. Italia 3318, Montevideo 11600, Uruguay,1 Institute of Genetics and Biophysics, Adriano Buzzati Traverso-CNR, Via Pietro Castellino 111, 80131 Naples, Italy,2 Laboratorio de Tecnología Molecular, Facultad de Ciencias, UdelaR, Iguá 4225, Montevideo 11400, Uruguay3

Received 25 February 2009/ Accepted 29 May 2009

The rhizobial DctA permease is essential for the development of effective nitrogen-fixing bacteroids, which was correlated with its requirement for growth on C4-dicarboxylates. A previously described dctA mutant of Rhizobium tropici CIAT899, strain GA1 (dctA), however, was unexpectedly still able to grow on succinate as a sole carbon source but less efficiently than CIAT899. Like other rhizobial dctA mutants, GA1 was unable to grow on fumarate or malate as a carbon source and induced the formation of ineffective nodules. We report an alternative succinate uptake system identified by Tn5 mutagenesis of strain GA1 that was required for the remaining ability to transport and utilize succinate. The alternative uptake system required a three-gene cluster that is highly characteristic of a dctABD locus. The predicted permease-encoding gene had high sequence similarity with open reading frames encoding putative 2-oxoglutarate permeases (KgtP) of Ralstonia solanacearum and Agrobacterium tumefaciens. This analysis was in agreement with the requirement for this gene for optimal growth on and induction by 2-oxoglutarate. The permease-encoding gene of the alternative system was also designated kgtP in R. tropici. The dctBD-like genes in this cluster were found to be required for kgtP expression and were designated kgtSR. Analysis of a kgtP::lacZ transcriptional fusion indicated that a kgtSR-dependent promoter of kgtP was specifically induced by 2-oxoglutarate. The expression of kgtPp was found in bacteroids of nodules formed with either CIAT899 or GA1 on roots of Phaseolus vulgaris. Results suggested that 2-oxoglutarate might be transported or conceivably exported in nodules induced by R. tropici on roots of P. vulgaris.

* Corresponding author. Mailing address: IIBCE, Av. Italia 3318, Montevideo 11600, Uruguay. Phone: 598 2 487 1616, ext. 145. Fax: 598 2 487 5548. E-mail: silvia{at}iibce.edu.uy

{triangledown} Published ahead of print on 5 June 2009.

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

Journal of Bacteriology, August 2009, p. 5057-5067, Vol. 191, No. 16
0021-9193/09/$08.00+0     doi:10.1128/JB.00252-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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