Hooper Sean D, Berg Otto G
Department of Molecular Evolution, EBC, Uppsala University, Norbyvägen 18C, SE-75236 Uppsala, Sweden.
J Mol Evol. 2002 Dec;55(6):734-44. doi: 10.1007/s00239-002-2369-2.
By comparing two strains of Escherichia coli (K12 and O157:H7) with an outgroup of Salmonella and Klebsiella species and analyzing the sets of genes which are present or absent in either of the three groups, we study the gene history of K12, in particular, since the respective divergences of these bacteria. Furthermore, by using a compositional method based on context bias, we evaluate not only recently imported genes but also deleted genes. In addition, we examine recent gene duplications in the two E. coli strains. It is found that turnover of DNA is high in E. coli and, more importantly, that turnover is highest for genes of low GC content. Although levels of import are high, most of the imported genes seem to be "junk" or have poorly understood functions. Nevertheless, selected genes do persist, and may even define some E. coli strains as pathogenic. Our results support the conclusion that some of the pathogenic islands in O157:H7 are likely to have been imported in recent time.
通过将两种大肠杆菌菌株（K12和O157:H7）与沙门氏菌和克雷伯氏菌属的一个外群进行比较，并分析这三组中存在或缺失的基因集，我们研究了K12的基因历史，特别是自这些细菌各自分化以来的历史。此外，通过使用基于上下文偏差的组成方法，我们不仅评估了最近导入的基因，还评估了缺失的基因。此外，我们检查了两种大肠杆菌菌株中最近的基因复制情况。研究发现，大肠杆菌的DNA周转率很高，更重要的是，低GC含量的基因周转率最高。尽管导入水平很高，但大多数导入的基因似乎是“垃圾”基因或功能尚不清楚。然而，某些特定的基因确实留存了下来，甚至可能将一些大肠杆菌菌株定义为致病菌株。我们的结果支持这样的结论，即O157:H7中的一些致病岛很可能是近期导入的。
