Department of Plant and Microbial Biology, University of California, Berkeley, Berkeley, CA 94720.
School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230.
Microbiol Spectr. 2015 Jun;3(3). doi: 10.1128/microbiolspec.VE-0010-2014.
Many Gram-positive and Gram-negative bacteria can become naturally competent to take up extracellular DNA from the environment via a dedicated uptake apparatus. The genetic material that is acquired can (i) be used for nutrients, (ii) aid in genome repair, and (iii) promote horizontal gene transfer when incorporated onto the genome by homologous recombination, the process of "transformation." Recent studies have identified multiple environmental cues sufficient to induce natural transformation in Vibrio cholerae and several other Vibrio species. In V. cholerae, nutrient limitation activates the cAMP receptor protein regulator, quorum-sensing signals promote synthesis of HapR-controlled QstR, chitin stimulates production of TfoX, and low extracellular nucleosides allow CytR to serve as an additional positive regulator. The network of signaling systems that trigger expression of each of these required regulators is well described, but the mechanisms by which each in turn controls competence apparatus genes is poorly understood. Recent work has defined a minimal set of genes that encode apparatus components and begun to characterize the architecture of the machinery by fluorescence microscopy. While studies with a small set of V. cholerae reference isolates have identified regulatory and competence genes required for DNA uptake, future studies may identify additional genes and regulatory connections, as well as revealing how common natural competence is among diverse V. cholerae isolates and other Vibrio species.
许多革兰氏阳性和革兰氏阴性细菌可以通过专门的摄取装置自然成为摄取环境中外源 DNA 的能力体。获得的遗传物质可以 (i) 用作营养物质，(ii) 有助于基因组修复，以及 (iii) 通过同源重组整合到基因组上时促进水平基因转移，这一过程称为“转化”。最近的研究已经确定了多种环境线索，足以在霍乱弧菌和其他几种弧菌物种中诱导自然转化。在霍乱弧菌中，营养限制激活 cAMP 受体蛋白调节剂，群体感应信号促进 HapR 控制的 QstR 的合成，几丁质刺激 TfoX 的产生，细胞外核苷的低浓度允许 CytR 作为额外的正调节剂。触发这些必需调节剂表达的信号系统网络描述得很好，但每个调节剂依次控制能力体基因的机制知之甚少。最近的工作定义了一组最小的基因，这些基因编码装置组件，并通过荧光显微镜开始表征该机器的结构。虽然对一小部分霍乱弧菌参考分离物的研究已经确定了 DNA 摄取所需的调节基因和能力基因，但未来的研究可能会发现其他基因和调节联系，并揭示常见的自然能力在不同的霍乱弧菌分离物和其他弧菌物种中的普遍性。
