State Key Laboratories for Agro-biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China.
BMC Microbiol. 2010 Jul 26;10:198. doi: 10.1186/1471-2180-10-198.
The chromosome of Streptomyces has been shown to be unstable, frequently undergoing gross chromosomal rearrangements. However, the mechanisms underlying this phenomenon remain unclear, with previous studies focused on two chromosomal ends as targets for rearrangements. Here we investigated chromosomal instability of Streptomyces avermitilis, an important producer of avermectins, and characterized four gross chromosomal rearrangement events, including a major deletion in the central region. The present findings provide a valuable contribution to the mechanistic study of genetic instability in Streptomyces.
Thirty randomly-selected "bald" mutants derived from the wild-type strain all contained gross chromosomal rearrangements of various types. One of the bald mutants, SA1-8, had the same linear chromosomal structure as the high avermectin-producing mutant 76-9. Chromosomes of both strains displayed at least three independent chromosomal rearrangements, including chromosomal arm replacement to form new 88-kb terminal inverted repeats (TIRs), and two major deletions. One of the deletions eliminated the 36-kb central region of the chromosome, but surprisingly did not affect viability of the cells. The other deletion (74-kb) was internal to the right chromosomal arm. The chromosome of another bald mutant, SA1-6, was circularized with deletions at both ends. No obvious homology was found in all fusion sequences. Generational stability analysis showed that the chromosomal structure of SA1-8 and SA1-6 was stable.
Various chromosomal rearrangements, including chromosomal arm replacement, interstitial deletions and chromosomal circularization, occurred in S. avermitilis by non-homologous recombination. The finding of an inner deletion involving in the central region of S. avermitilis chromosome suggests that the entire Streptomyces chromosome may be the target for rearrangements, which are not limited, as previously reported, to the two chromosomal ends.
链霉菌的染色体已被证明不稳定，经常发生巨大的染色体重排。然而，这一现象的机制尚不清楚，以前的研究集中在两个染色体末端作为重排的靶点。在这里，我们研究了阿维链霉菌的染色体不稳定性，阿维链霉菌是阿维菌素的重要生产者，并对四个巨大的染色体重排事件进行了特征描述，包括在中央区域的一个主要缺失。本研究结果为链霉菌遗传不稳定性的机制研究提供了有价值的贡献。
从野生型菌株中随机挑选的 30 个“秃发”突变体都含有各种类型的巨大染色体重排。其中一个秃发突变体 SA1-8 与高产阿维菌素突变体 76-9 具有相同的线性染色体结构。这两种菌株的染色体都显示出至少三种独立的染色体重排，包括染色体臂替换形成新的 88kb 末端反向重复（TIR），以及两个主要缺失。其中一个缺失消除了染色体的 36kb 中央区域，但令人惊讶的是，这并没有影响细胞的活力。另一个缺失（74kb）位于右侧染色体臂内部。另一个秃发突变体 SA1-6 的染色体两端缺失，形成了环状。在所有融合序列中都没有发现明显的同源性。代际稳定性分析表明，SA1-8 和 SA1-6 的染色体结构是稳定的。
阿维链霉菌中发生了各种染色体重排，包括染色体臂替换、中间缺失和染色体环化，这些重排是通过非同源重组发生的。在阿维链霉菌染色体中央区域发生内部缺失的发现表明，整个链霉菌染色体可能是重排的靶点，而不是以前报道的仅限于两个染色体末端。
