Marlow Victoria L, Haag Andreas F, Kobayashi Hajime, Fletcher Vivien, Scocchi Marco, Walker Graham C, Ferguson Gail P
Institute of Medical Sciences, University of Aberdeen, Foresterhill, United Kingdom.
J Bacteriol. 2009 Mar;191(5):1519-27. doi: 10.1128/JB.01661-08. Epub 2008 Dec 12.
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.
内膜蛋白BacA对于苜蓿中华根瘤菌和流产布鲁氏菌分别在植物和哺乳动物宿主体内建立慢性细胞内感染至关重要。在其自由生活状态下，缺乏BacA的苜蓿中华根瘤菌和流产布鲁氏菌突变体的外膜脂多糖A超长链脂肪酸（VLCFA）含量降低，并且与各自的亲本菌株相比，对糖肽博来霉素表现出低水平抗性。在本文中，我们研究了BacA参与苜蓿中华根瘤菌肽摄取的假说。我们确定苜蓿中华根瘤菌ΔbacA突变体对真核肽Bac7的截短形式Bac7(1-16)完全抗性，并且这种表型似乎与其脂多糖A改变无关。随后，我们发现BacA和/或大肠杆菌SbmA对于苜蓿中华根瘤菌中荧光标记的Bac7(1-16)摄取至关重要。鉴于豆科宿主内有数百种根瘤特异性肽，我们的数据表明BacA介导的肽摄取可能在苜蓿中华根瘤菌的慢性感染过程中起核心作用。然而，由于我们确定两个共生缺陷的苜蓿中华根瘤菌bacA定点突变体（分别具有Q193G和R389G突变），其脂多糖A VLCFA含量已知降低，但仍能够摄取肽，这些发现表明依赖BacA的肽摄取不能完全解释BacA在豆科植物共生中的重要作用。此外，它们提供了证据表明导致苜蓿中华根瘤菌脂多糖A VLCFA修饰的BacA功能在豆科植物的慢性感染中起关键作用。
