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Journal of Bacteriology, March 2009, p. 1547-1555, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.00926-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Characterization of a {gamma}-Aminobutyric Acid Transport System of Rhizobium leguminosarum bv. viciae 3841{triangledown}

J. P. White,1 J. Prell,2 V. K. Ramachandran,1 and P. S. Poole2*

School of Biological Sciences, University of Reading, Reading RG6 6AJ, United Kingdom,1 Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom2

Received 7 July 2008/ Accepted 9 December 2008

Spontaneous mutants of Rhizobium leguminosarum bv. viciae 3841 were isolated that grow faster than the wild type on {gamma}-aminobutyric acid (GABA) as the sole carbon and nitrogen source. These strains (RU1736 and RU1816) have frameshift mutations (gtsR101 and gtsR102, respectively) in a GntR-type regulator (GtsR) that result in a high rate of constitutive GABA transport. Tn5 mutagenesis and quantitative reverse transcription-PCR showed that GstR regulates expression of a large operon (pRL100242 to pRL100252) on the Sym plasmid that is required for GABA uptake. An ABC transport system, GtsABCD (for GABA transport system) (pRL100248-51), of the spermidine/putrescine family is part of this operon. GtsA is a periplasmic binding protein, GtsB and GtsC are integral membrane proteins, and GtsD is an ATP-binding subunit. Expression of gtsABCD from a lacZ promoter confirmed that it alone is responsible for high rates of GABA transport, enabling rapid growth of strain 3841 on GABA. Gts transports open-chain compounds with four or five carbon atoms with carboxyl and amino groups at, or close to, opposite termini. However, aromatic compounds with similar spacing between carboxyl and amino groups are excellent inhibitors of GABA uptake so they may also be transported. In addition to the ABC transporter, the operon contains two putative mono-oxygenases, a putative hydrolase, a putative aldehyde dehydrogenase, and a succinate semialdehyde dehydrogenase. This suggests the operon may be involved in the transport and breakdown of a more complex precursor to GABA. Gts is not expressed in pea bacteroids, and gtsB mutants are unaltered in their symbiotic phenotype, suggesting that Bra is the only GABA transport system available for amino acid cycling.

* Corresponding author. Mailing address: Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Colney, Norwich NR4 7UH, United Kingdom. Phone: 44 (0)1603 450719. Fax: 44 (0)1603 450778. E-mail: philip.poole{at}bbsrc.ac.uk

{triangledown} Published ahead of print on 19 December 2008.

Journal of Bacteriology, March 2009, p. 1547-1555, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.00926-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Prell, J., Bourdes, A., Karunakaran, R., Lopez-Gomez, M., Poole, P. (2009). Pathway of {gamma}-Aminobutyrate Metabolism in Rhizobium leguminosarum 3841 and Its Role in Symbiosis. J. Bacteriol. 191: 2177-2186 [Abstract] [Full Text]  


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