Center for Pharmaceutical Biotechnology, College of Pharmacy, University of Illinois at Chicago, Chicago, Illinois, USA.
J Bacteriol. 2012 Sep;194(17):4589-600. doi: 10.1128/JB.00830-12. Epub 2012 Jun 22.
Horizontal gene transfer is an important means of bacterial evolution that is facilitated by transduction, conjugation, and natural genetic transformation. Transformation occurs after bacterial cells enter a state of competence, where naked DNA is acquired from the extracellular environment. Induction of the competent state relies on signals that activate master regulators, causing the expression of genes involved in DNA uptake, processing, and recombination. All streptococcal species contain the master regulator SigX and SigX-dependent effector genes required for natural genetic transformation; however, not all streptococcal species have been shown to be naturally competent. We recently demonstrated that competence development in Streptococcus mutans requires the type II ComRS quorum-sensing circuit, comprising an Rgg transcriptional activator and a novel peptide pheromone (L. Mashburn-Warren, D. A. Morrison, and M. J. Federle, Mol. Microbiol. 78:589-606, 2010). The type II ComRS system is shared by the pyogenic, mutans, and bovis streptococci, including the clinically relevant pathogen Streptococcus pyogenes. Here, we describe the activation of sigX by a small-peptide pheromone and an Rgg regulator of the type II ComRS class. We confirm previous reports that SigX is functional and able to activate sigX-dependent gene expression within the competence regulon, and that SigX stability is influenced by the cytoplasmic protease ClpP. Genomic analyses of available S. pyogenes genomes revealed the presence of intact genes within the competence regulon. While this is the first report to show natural induction of sigX, S. pyogenes remained nontransformable under laboratory conditions. Using radiolabeled DNA, we demonstrate that transformation is blocked at the stage of DNA uptake.
水平基因转移是细菌进化的一种重要手段，它通过转导、共轭和自然遗传转化来实现。转化发生在细菌细胞进入感受态后，此时裸 DNA 从细胞外环境中被获取。感受态的诱导依赖于激活主调控因子的信号，导致参与 DNA 摄取、加工和重组的基因表达。所有链球菌都含有自然遗传转化所需的主调控因子 SigX 和 SigX 依赖性效应基因；然而，并非所有链球菌都被证明具有自然转化能力。我们最近证明，变形链球菌的感受态发育需要 II 型 ComRS 群体感应电路，该电路由 Rgg 转录激活因子和一种新型肽类信息素（L. Mashburn-Warren、D. A. Morrison 和 M. J. Federle，Mol. Microbiol. 78:589-606, 2010）组成。II 型 ComRS 系统由化脓性、变异和牛链球菌共享，包括临床相关病原体酿脓链球菌。在这里，我们描述了小肽类信息素和 II 型 ComRS 类 Rgg 调节剂对 sigX 的激活。我们证实了之前的报道，即 SigX 是功能性的，能够在感受态调控子内激活 sigX 依赖性基因表达，并且 SigX 的稳定性受细胞质蛋白酶 ClpP 的影响。对现有酿脓链球菌基因组的基因组分析显示，感受态调控子内存在完整的基因。虽然这是第一个报道表明自然诱导 sigX 的报告，但在实验室条件下，酿脓链球菌仍然不可转化。使用放射性标记的 DNA，我们证明转化在 DNA 摄取阶段受阻。
