Distribution of chromosome length variation in natural isolates of Escherichia coli
Distribution of chromosome length variation in natural isolates of Escherichia coli
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DOI：
10.1093/oxfordjournals.molbev.a025847
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发表时间：
1998-01-01
影响因子：
10.7
通讯作者：
Ochman, H
中科院分区：
文献类型：
--
作者：
Bergthorsson, U;Ochman, H
通过使用位点仅限于 rDNA 操纵子的限制性内切酶进行物理作图，分析了 35 个大肠杆菌天然分离株中染色体大小的大规模变异。尽管实验室菌株大肠杆菌 K12 和肠沙门氏菌 sv、鼠伤寒沙门氏菌 LT2 的遗传图谱和染色体长度高度一致，但大肠杆菌天然菌株之间的染色体长度差异可能高达 1 Mb，长度范围为 4.5 至 5.5 Mb。这种变异是由分散在整个基因组中的多种变化产生的，并且这些变化是相关的；即，对染色体的一部分的添加常常伴随着对其他染色体区域的添加。这种变异模式很可能是选择作用的结果，该选择作用是为了保持环状染色体两侧的复制起点和终点之间的距离相等。观察到的大小差异存在很大的系统发育成分：来自大肠杆菌某些亚群的天然分离株始终具有较大的染色体，这表明较大染色体中的许多额外 DNA 是通过共同祖先共享的。基因组大小和生长速率之间没有显着的相关性，这反驳了细菌基因组的精简是对自然种群更快生长速率选择的反应的观点。
Large-scale variation in chromosome size was analyzed in 35 natural isolates of Escherichia coli by physical mapping with a restriction enzyme whose sites are restricted to rDNA operons. Although the genetic maps and chromosome lengths of the laboratory strains E. coli K12 and Salmonella enterica sv, Typhimurium LT2 are highly congruent, chromosome lengths among natural strains of E. coli can differ by as much as 1 Mb, ranging from 4.5 to 5.5 Mb in length. This variation has been generated by multiple changes dispersed throughout the genome, and these alterations are correlated; i.e., additions to one portion of the chromosome are often accompanied by additions to other chromosomal regions. This pattern of variation is most probably the result of selection acting to maintain equal distances between the replication origin and terminus on each side of the circular chromosome. There is a large phylogenetic component to the observed size variation: natural isolates from certain subgroups of E. coli have consistently larger chromosomes, suggesting that much of the additional DNA in larger chromosomes is shared through common ancestry. There is no significant correlation between genome sizes and growth rates, which counters the view that the streamlining of bacterial genomes is a response to selection for faster growth rates in natural populations.