Department of Plant and Microbial Biology, University of California, Berkeley, USA.
Department of Environmental Science, Policy and Management, University of California, Berkeley, USA.
Microbiology (Reading). 2014 Jan;160(Pt 1):37-46. doi: 10.1099/mic.0.070581-0. Epub 2013 Oct 22.
For naturally competent bacteria, spatially structured growth can provide an environment for enhanced horizontal gene transfer through transformation and recombination. DNA is often present in the extracellular environment, such as in the extracellular matrix of biofilms, and the lysis of a single cell can result in high local DNA concentrations. Xylella fastidiosa is a naturally competent plant pathogen that typically lives in a surface-attached state, yet previous work characterizing the competence of this organism was conducted with planktonic cells in liquid environments. Here, we show that transformation and recombination efficiencies are two to three orders of magnitude higher for cells grown on solid compared with liquid media, with maximum recombination efficiencies of about 10(-3). Cells were highly competent throughout their exponential growth phase, with no significant change in recombination efficiencies until population growth rates began to slow. Mutations in type IV pili, competency-related, and cell-cell signalling genes significantly impacted the ability of X. fastidiosa to acquire and incorporate DNA. Because X. fastidiosa is highly competent when growing in a surface-attached state, as it does within its insect vectors and host plants, recombination of naturally transformed DNA could be a significant route by which horizontal gene transfer occurs in natural environments.
对于自然感受态细菌，空间结构的生长可以通过转化和重组提供一个增强水平基因转移的环境。DNA 通常存在于细胞外环境中，例如生物膜的细胞外基质中，单个细胞的裂解会导致局部 DNA 浓度升高。木质部难养菌是一种天然感受态植物病原体，通常以附着在表面的状态存在，但之前对该生物体感受态的特征描述是在液体环境中的浮游细胞中进行的。在这里，我们表明，与液体培养基相比，固体培养基上细胞的转化和重组效率高两个到三个数量级，最大重组效率约为 10(-3)。细胞在整个指数生长期都具有高感受态，直到种群生长速率开始减慢，重组效率才没有明显变化。IV 型菌毛、与感受态相关的和细胞间信号转导基因的突变显著影响木质部难养菌获取和整合 DNA 的能力。因为木质部难养菌在附着状态下生长时具有很高的感受态，就像它在昆虫载体和宿主植物中一样，自然转化 DNA 的重组可能是水平基因转移在自然环境中发生的一个重要途径。
