Department of Population Medicine and Diagnostic Sciences, Cornell University, Ithaca, New York, USA.
Genome Biol Evol. 2010;2:646-55. doi: 10.1093/gbe/evq048. Epub 2010 Aug 4.
Defining bacterial species and understanding the relative cohesiveness of different components of their genomes remains a fundamental problem in microbiology. Bacterial species tend to be comprised of both a set of core and dispensable genes, with the sum of these two components forming the species pan-genome. The role of the core and dispensable genes in defining bacterial species and the question of whether pan-genomes are finite or infinite remain unclear. Here we demonstrate, through the analysis of 96 genome sequences derived from two closely related sympatric sister species of pathogenic bacteria (Campylobacter coli and C. jejuni), that their pan-genome is indeed finite and that there are unique and cohesive features to each of their genomes defining their genomic identity. The two species have a similar pan-genome size; however, C. coli has acquired a larger core genome and each species has evolved a number of species-specific core genes, possibly reflecting different adaptive strategies. Genome-wide assessment of the level of lateral gene transfer within and between the two sister species, as well as within the core and non-core genes, demonstrates a resistance to interspecies recombination in the core genome of the two species and therefore provides persuasive support for the core genome hypothesis for bacterial species.
定义细菌物种以及理解其基因组不同组成部分的相对内聚性仍然是微生物学中的一个基本问题。细菌物种通常由一组核心基因和可分配基因组成，这两个组成部分的总和构成了物种泛基因组。核心基因和可分配基因在定义细菌物种中的作用以及泛基因组是否有限或无限的问题仍不清楚。在这里，我们通过对来自两种密切相关的共生姐妹种（致病性细菌弯曲杆菌和空肠弯曲杆菌）的 96 个基因组序列的分析表明，它们的泛基因组确实是有限的，并且它们的每个基因组都具有独特且有凝聚力的特征，从而定义了其基因组的身份。这两个物种具有相似的泛基因组大小；然而，空肠弯曲杆菌获得了更大的核心基因组，每个物种都进化出了一些物种特异性的核心基因，这可能反映了不同的适应策略。对这两个姐妹种之间以及核心基因和非核心基因内的水平基因转移程度的全基因组评估表明，两种物种的核心基因组对种间重组具有抵抗力，因此为细菌物种的核心基因组假说提供了有力支持。
