Lorenzi Jean-Noël, Lespinet Olivier, Leblond Pierre, Thibessard Annabelle
Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), 91198, Gif-sur-Yvette, France.
Université de Lorraine, INRAE, DynAMic, F-54000 Nancy, France.
Microb Genom. 2019 Sep;7(6). doi: 10.1099/mgen.0.000525.
possess a large linear chromosome (6-12 Mb) consisting of a conserved central region flanked by variable arms covering several megabases. In order to study the evolution of the chromosome across evolutionary times, a representative panel of strains and species (125) whose chromosomes are completely sequenced and assembled was selected. The pan-genome of the genus was modelled and shown to be open with a core-genome reaching 1018 genes. The evolution of chromosome was analysed by carrying out pairwise comparisons, and by monitoring indexes measuring the conservation of genes (presence/absence) and their synteny along the chromosome. Using the phylogenetic depth offered by the chosen panel, it was possible to infer that within the central region of the chromosome, the core-genes form a highly conserved organization, which can reveal the existence of an ancestral chromosomal skeleton. Conversely, the chromosomal arms, enriched in variable genes evolved faster than the central region under the combined effect of rearrangements and addition of new information from horizontal gene transfer. The genes hosted in these regions may be localized there because of the adaptive advantage that their rapid evolution may confer. We speculate that (i) within a bacterial population, the variability of these genes may contribute to the establishment of social characters by the production of 'public goods' (ii) at the evolutionary scale, this variability contributes to the diversification of the genetic pool of the bacteria.
拥有一条大型线性染色体（6 - 12兆碱基对），其由一个保守的中央区域组成，两侧是覆盖几个兆碱基的可变臂。为了研究该染色体在进化时间中的演变，选择了一组具有代表性的菌株和物种（125个），其染色体已完全测序和组装。对该属的泛基因组进行建模，结果表明其是开放的，核心基因组有1018个基因。通过进行成对比较，并监测衡量基因保守性（存在/缺失）及其在染色体上的共线性的指标，来分析染色体的进化。利用所选样本提供的系统发育深度，可以推断在染色体的中央区域内，核心基因形成了高度保守的组织，这可以揭示祖先染色体骨架的存在。相反，富含可变基因的染色体臂在重排和水平基因转移新信息添加的共同作用下，比中央区域进化得更快。这些区域中存在的基因可能因其快速进化可能带来的适应性优势而定位在此处。我们推测：（i）在细菌群体中，这些基因的变异性可能通过产生“公共物品”来促进社会特征的建立；（ii）在进化尺度上，这种变异性有助于细菌基因库的多样化。
