Micalis Institute, INRA, AgroParisTech, Université Paris-Saclay, 78350 Jouy-en-Josas, France.
MaIAGE, INRA, Université Paris-Saclay, 78350 Jouy-en-Josas, France.
Sci Rep. 2017 Mar 10;7:44331. doi: 10.1038/srep44331.
The first Lactobacillus delbrueckii ssp. bulgaricus genome sequence revealed the presence of a very large inverted repeat (IR), a DNA sequence arrangement which thus far seemed inconceivable in a non-manipulated circular bacterial chromosome, at the replication terminus. This intriguing observation prompted us to investigate if similar IRs could be found in other bacteria. IRs with sizes varying from 38 to 76 kbp were found at the replication terminus of all 5 L. delbrueckii ssp. bulgaricus chromosomes analysed, but in none of 1373 other chromosomes. They represent the first naturally occurring very large IRs detected in circular bacterial genomes. A comparison of the L. bulgaricus replication terminus regions and the corresponding regions without IR in 5 L. delbrueckii ssp. lactis genomes leads us to propose a model for the formation and evolution of the IRs. The DNA sequence data are consistent with a novel model of chromosome rescue after premature replication termination or irreversible chromosome damage near the replication terminus, involving mechanisms analogous to those proposed in the formation of very large IRs in human cancer cells. We postulate that the L. delbrueckii ssp. bulgaricus-specific IRs in different strains derive from a single ancestral IR of at least 93 kbp.
第一个德氏乳杆菌保加利亚亚种的基因组序列揭示了在复制末端存在一个非常大的反向重复（IR），这是一种迄今为止在非人为操作的圆形细菌染色体中似乎不可思议的 DNA 序列排列。这一有趣的观察结果促使我们研究是否可以在其他细菌中找到类似的 IR。在分析的所有 5 个德氏乳杆菌保加利亚亚种的染色体复制末端都发现了大小在 38 到 76kbp 之间的 IR，但在 1373 个其他染色体中均未发现。它们代表了在圆形细菌基因组中首次发现的天然存在的非常大的 IR。对保加利亚德氏乳杆菌复制末端区域和无 IR 的相应区域与 5 个德氏乳杆菌乳亚种乳糖酶基因组的比较，使我们提出了一个关于 IR 形成和进化的模型。DNA 序列数据与复制末端附近过早复制终止或不可逆染色体损伤后染色体挽救的新模型一致，涉及与在人类癌细胞中形成非常大的 IR 中提出的机制类似的机制。我们推测，不同菌株中保加利亚德氏乳杆菌亚种特异性的 IR 源自至少 93kbp 的单个祖先 IR。
