Essential role for the BacA protein in the uptake of a truncated eukaryotic peptide in Sinorhizobium meliloti.
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 DeltabacA 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.
Marlow
Victoria L
VL
Institute of Medical Sciences, University of Aberdeen, Foresterhill, United Kingdom.
Haag
Andreas F
AF
Kobayashi
Hajime
H
Fletcher
Vivien
V
Scocchi
Marco
M
Walker
Graham C
GC
Ferguson
Gail P
GP
D000595:Amino Acid Sequence; D000818:Animals; D000890:Anti-Infective Agents / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests / Q000379:methods; D008969:Molecular Sequence Data; D009154:Mutation; D009504:Neutrophils / Q000737:chemistry*; D010456:Peptides, Cyclic / Q000737:chemistry / Q000378:metabolism* / Q000494:pharmacology; D016962:Sinorhizobium meliloti / Q000187:drug effects* / Q000254:growth & development / Q000378:metabolism
D000890:Anti-Infective Agents; D001426:Bacterial Proteins; D026901:Membrane Transport Proteins; D010456:Peptides, Cyclic; C082397:bacA protein, Rhizobium meliloti; C056454:bactenecin