Université de Lyon, CNRS UMR 5240, Université Lyon 1, 10 rue Dubois F-69622 Villeurbanne, France.
UMR1319 MICALIS, INRA, Centre de Recherches de Jouy-en-Josas, 78352 Jouy-en-Josas Cedex, France.
Microbiology (Reading). 2011 Jun;157(Pt 6):1612-1619. doi: 10.1099/mic.0.048173-0. Epub 2011 Mar 10.
Lactococcus lactis is known to take up extracellular peptides via at least three distinct peptide transporters. The well-described oligopeptide transporter Opp alone is able to ensure the growth of L. lactis in milk, while the di- and tripeptide transporter DtpT is involved in a peptide-dependent signalling mechanism. The oligopeptide Opt transporter displays two peptide-binding proteins, OptA and OptS. We previously demonstrated that OptA-dependent transport is dedicated to nutritional peptides, as an optABCDF mutant (of a strain devoid of Opp) has an impaired capacity to grow in milk. Using isogenic peptide transport mutants, this study shows that biosynthesis of the Opt transporter is much less sensitive to downregulation that is dependent on extracellular peptides taken up by DtpT than is Opp biosynthesis; this peptide-dependent regulation relies on the transcriptional repressor CodY. We demonstrate the dual function of the Opt system; while OptA contributes to the bacterial nutrition during growth in milk, OptS is involved in the transport of signalling peptides derived from milk and controlling opp expression. So, these results shed new light on the peptide-dependent regulation relying on two peptide transporters with different specificities: DtpT and Opt (via OptS).
乳球菌已知至少通过三种不同的肽转运体摄取细胞外肽。描述良好的寡肽转运体 Opp 本身能够确保乳球菌在牛奶中的生长，而二肽和三肽转运体 DtpT 则参与肽依赖的信号机制。寡肽 Opt 转运体显示出两种肽结合蛋白 OptA 和 OptS。我们之前证明，OptA 依赖的转运专门用于营养肽，因为缺乏 Opp 的 optABCDF 突变体（菌株）在牛奶中的生长能力受损。使用同源肽转运突变体，本研究表明，Opt 转运体的生物合成对依赖于 DtpT 摄取的细胞外肽的下调的敏感性要低于 Opp 生物合成；这种肽依赖的调节依赖于转录抑制剂 CodY。我们证明了 Opt 系统的双重功能；虽然 OptA 有助于细菌在牛奶中生长时的营养，但 OptS 参与了源自牛奶的信号肽的转运，并控制 opp 表达。因此，这些结果为依赖于具有不同特异性的两种肽转运体（DtpT 和 Opt（通过 OptS））的肽依赖性调节提供了新的见解。
