Moran Nancy A, McLaughlin Heather J, Sorek Rotem
Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, AZ 85721, USA.
Science. 2009 Jan 16;323(5912):379-82. doi: 10.1126/science.1167140.
Among cellular organisms, symbiotic bacteria provide the extreme examples of genome degradation and reduction. However, only isolated snapshots of eroding symbiont genomes have previously been available. We documented the dynamics of symbiont genome evolution by sequencing seven strains of Buchnera aphidicola from pea aphid hosts. We estimated a spontaneous mutation rate of at least 4 x 10(-9) substitutions per site per replication, which is more than 10 times as high as the rates previously estimated for any bacteria. We observed a high rate of small insertions and deletions associated with abundant DNA homopolymers, and occasional larger deletions. Although purifying selection eliminates many mutations, some persist, resulting in ongoing loss of genes and DNA from this already tiny genome. Our results provide a general model for the stepwise process leading to genome reduction.
在细胞生物中，共生细菌展现了基因组退化和缩减的极端例子。然而，此前仅能获得正在衰退的共生体基因组的孤立片段。我们通过对来自豌豆蚜宿主的七种蚜虫内共生菌（Buchnera aphidicola）菌株进行测序，记录了共生体基因组进化的动态过程。我们估计每个复制位点的自发突变率至少为4×10⁻⁹ 替换，这比之前对任何细菌估计的突变率高出10倍以上。我们观察到与大量DNA同聚物相关的高频率小插入和缺失，以及偶尔出现的较大缺失。尽管纯化选择消除了许多突变，但仍有一些突变留存，导致这个原本就很小的基因组持续丢失基因和DNA。我们的研究结果为导致基因组缩减的逐步过程提供了一个通用模型。
