Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
Environ Microbiol Rep. 2011 Dec;3(6):744-9. doi: 10.1111/j.1758-2229.2011.00293.x. Epub 2011 Sep 27.
The marine cyanobacterium Prochlorococcus, the smallest and most abundant oxygenic phototroph, has an extremely streamlined genome and a high rate of protein evolution. High-light adapted strains of Prochlorococcus in particular have seemingly inadequate DNA repair systems, raising the possibility that inadequate repair may lead to high mutation rates. Prochlorococcus mutation rates have been difficult to determine, in part because traditional methods involving quantifying colonies on solid selective media are not straightforward for this organism. Here we used a liquid dilution method to measure the approximate number of antibiotic-resistant mutants in liquid cultures of Prochlorococcus strains previously unexposed to antibiotic selection. Several antibiotics for which resistance in other bacteria is known to result from a single base pair change were used. The resulting frequencies of antibiotic resistance in Prochlorococcus cultures allowed us to then estimate maximum spontaneous mutation rates, which were similar to those in organisms such as E. coli (∼5.4 × 10(-7) per gene per generation). Therefore, despite the lack of some DNA repair genes, it appears unlikely that the Prochlorcoccus genomes studied here are currently being shaped by unusually high mutation rates.
海洋蓝细菌聚球藻是最小和最丰富的需氧光合生物，其基因组极为精简，并且具有很高的蛋白质进化速率。特别是适应高光的聚球藻菌株似乎具有不充分的 DNA 修复系统，这增加了修复不足可能导致高突变率的可能性。聚球藻的突变率一直难以确定，部分原因是传统的方法涉及在固体选择性培养基上量化菌落，对于这种生物体来说并不简单。在这里，我们使用液体稀释法来测量以前未暴露于抗生素选择的聚球藻菌株的液体培养物中抗生素抗性突变体的近似数量。使用了几种抗生素，已知其他细菌的抗生素抗性是由单个碱基对变化引起的。聚球藻培养物中抗生素抗性的产生频率使我们能够估算最大的自发突变率，这与大肠杆菌等生物体相似（每个基因每代约为 5.4×10(-7)）。因此，尽管缺乏一些 DNA 修复基因，但这里研究的聚球藻基因组似乎不太可能受到异常高突变率的影响。
