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Journal of Bacteriology, March 2009, p. 1519-1527, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01661-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Essential Role for the BacA Protein in the Uptake of a Truncated Eukaryotic Peptide in Sinorhizobium meliloti{triangledown}

Victoria L. Marlow,1 Andreas F. Haag,1 Hajime Kobayashi,2 Vivien Fletcher,1 Marco Scocchi,3 Graham C. Walker,2 and Gail P. Ferguson1*

School of Medicine & Dentistry, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, United Kingdom,1 Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139,2 Department of Life Sciences, University of Trieste, Via Giorgieri 1, 34127 Trieste, Italy3

Received 25 November 2008/ Accepted 4 December 2008

The inner membrane BacA protein is essential for the establishment of chronic intracellular infections by Sinorhizobium meliloti and Brucella abortus within plant and mammalian hosts, respectively. In their free-living state, S. meliloti and B. abortus mutants lacking BacA have reductions in their outer membrane lipid A very-long-chain fatty acid (VLCFA) contents and exhibit low-level resistance to the glycopeptide bleomycin in comparison to their respective parent strains. In this paper we investigate the hypothesis that BacA is involved in peptide uptake in S. meliloti. We determined that an S. meliloti {Delta}bacA mutant is completely resistant to a truncated form of the eukaryotic peptide Bac7, Bac7(1-16), and this phenotype appears to be independent of its lipid A alteration. Subsequently, we discovered that BacA and/or Escherichia coli SbmA is essential for fluorescently labeled Bac7(1-16) uptake in S. meliloti. Given that there are hundreds of root nodule-specific peptides within the legume host, our data suggest that BacA-mediated peptide uptake could play a central role in the chronic infection process of S. meliloti. However, since we determined that two symbiotically defective S. meliloti bacA site-directed mutants (with the Q193G and R389G mutations, respectively) with known reductions in their lipid A VLCFA contents are still capable of peptide uptake, these findings suggest that BacA-dependent peptide uptake cannot fully account for the essential role of BacA in the legume symbiosis. Further, they provide evidence that the BacA function that leads to the S. meliloti lipid A VLCFA modification plays a key role in the chronic infection of legumes.

* Corresponding author. Mailing address: School of Medicine, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, United Kingdom. Phone: 44 1224 559147. Fax: 44 1224 555766. E-mail: g.ferguson{at}abdn.ac.uk

{triangledown} Published ahead of print on 12 December 2008.

Journal of Bacteriology, March 2009, p. 1519-1527, Vol. 191, No. 5
0021-9193/09/$08.00+0     doi:10.1128/JB.01661-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Haag, A. F., Wehmeier, S., Beck, S., Marlow, V. L., Fletcher, V., James, E. K., Ferguson, G. P. (2009). The Sinorhizobium meliloti LpxXL and AcpXL Proteins Play Important Roles in Bacteroid Development within Alfalfa. J. Bacteriol. 191: 4681-4686 [Abstract] [Full Text]  


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