Department of Plant and Microbial Biology, University of California, Berkeley, CA, USA.
Appl Environ Microbiol. 2013 Mar;79(5):1712-7. doi: 10.1128/AEM.03525-12. Epub 2013 Jan 11.
Horizontally transferred DNA acquired through transformation and recombination has the potential to contribute to the diversity and evolution of naturally competent bacteria. However, many different factors affect the efficiency with which DNA can be transformed and recombined. In this study, we determined how the size of both homologous and nonhomologous regions affects transformation and recombination efficiencies in Xylella fastidiosa, a naturally competent generalist pathogen responsible for many emerging plant diseases. Our experimental data indicate that 96 bp of flanking homology is sufficient to initiate recombination, with recombination efficiencies increasing exponentially with the size of the homologous flanking region up to 1 kb. Recombination efficiencies also decreased with the size of the nonhomologous insert, with no recombination detected when 6 kb of nonhomologous DNA was flanked on either side by 1 kb of homologous sequences. Upon analyzing sequenced X. fastidiosa subsp. fastidiosa genomes for evidence of allele conversion, we estimated the mean size of recombination events to be 1,906 bp, with each event modifying, on average, 1.79% of the nucleotides in the recombined region. There is increasing evidence that horizontally acquired genes significantly affect the genetic diversity of X. fastidiosa, and DNA acquired through natural transformation could be a prominent mode of this horizontal transfer.
通过转化和重组获得的水平转移 DNA 有可能为自然感受态细菌的多样性和进化做出贡献。然而，许多不同的因素会影响 DNA 转化和重组的效率。在这项研究中，我们确定了同源和非同源区域的大小如何影响木质部细菌（一种负责许多新兴植物病害的自然感受态普通病原体）的转化和重组效率。我们的实验数据表明，96bp 的侧翼同源性足以启动重组，随着同源侧翼区域大小的增加，重组效率呈指数级增长，最大可达 1kb。重组效率也随非同源插入物的大小而降低，当 6kb 的非同源 DNA 两侧分别由 1kb 的同源序列包围时，检测不到重组。在分析木质部细菌亚种 fastidiosa 的测序基因组中是否存在等位基因转换的证据时，我们估计重组事件的平均大小为 1906bp，每个事件平均改变重组区域中 1.79%的核苷酸。越来越多的证据表明，水平获得的基因显著影响木质部细菌的遗传多样性，而通过自然转化获得的 DNA 可能是这种水平转移的主要模式。
