The Temporal Dynamics of Slightly Deleterious Mutations in Escherichia coli and Shigella spp.
The Temporal Dynamics of Slightly Deleterious Mutations in Escherichia coli and Shigella spp.
复制标题
DOI：
10.1093/molbev/msn252
复制
发表时间：
2009-02-01
影响因子：
10.7
通讯作者：
Feil, Edward J.
中科院分区：
文献类型：
--
作者：
Balbi, Kevin J.;Rocha, Eduardo P. C.;Feil, Edward J.
志贺氏菌是最近出现的大肠杆菌的克隆，它独立地采用了细胞内的致病生活方式。我们通过比较代表5个大肠杆菌和4个志贺氏菌基因组交集的2,098个直系物中独特多态的归一化、方向性频率分布，检验了这种利基专门化的分子进化后果。我们注意到志贺氏菌基因组中过多的AT富集性变化(GC>；AT)、颠换和非同义变化。通过在时间框架内检验这些差异，我们得出的结论是，我们的结果与志贺氏菌由于有效种群数量减少而放松或低效的选择是一致的。讨论了不同的解释，以及有趣的宋内氏志贺氏菌例外。最后，这一分析支持了这样的观点，即核苷酸组成通常不处于突变平衡，但选择在维持较高的GC含量方面发挥了作用，而不是仅仅由突变偏向造成的。这一论点对提纯选择非常弱的细菌内共生体基因组中腺嘌呤和胸腺嘧啶的富集性提供了启示。
The Shigella are recently emerged clones of Escherichia coli, which have independently adopted an intracellular pathogenic lifestyle. We examined the molecular evolutionary consequences of this niche specialization by comparing the normalized, directional frequency profiles of unique polymorphisms within 2,098 orthologues representing the intersection of five E. coli and four Shigella genomes. We note a surfeit of AT-enriching changes (GC -> AT), transversions, and nonsynonymous changes in the Shigella genomes. By examining these differences within a temporal framework, we conclude that our results are consistent with relaxed or inefficient selection in Shigella owing to a reduced effective population size. Alternative interpretations, and the interesting exception of Shigella sonnei, are discussed. Finally, this analysis lends support to the view that nucleotide composition typically does not lie at mutational equilibrium but that selection plays a role in maintaining a higher GC content than would result solely from mutation bias. This argument sheds light on the enrichment of adenine and thymine in the genomes of bacterial endosymbionts where purifying selection is very weak.