Muller's ratchet decreases fitness of a DNA-based microbe

摘要: Muller proposed that an asexual organism will inevitably accumulate deleterious mutations, resulting in increase of the mutational load and inexorable, ratchet-like, loss least mutated class [Muller, H.J. (1964) Mutat. Res. 1, 2-9]. The operation Muller's ratchet on real populations has been experimentally demonstrated only RNA viruses. However, these cases are exceptional mutation rates viruses extremely high. We have examined whether operates Salmonella typhimurium, a DNA-based with more typical genomic rate. Cells were grown asexually under conditions expected to result high genetic drift, was determined. S. typhimurium accumulated mutations such after 1700 generations, 1% 444 lineages tested had suffered obvious fitness, as determined by decreased growth These results suggest absence sex mechanisms, back or compensatory cannot compensate for accumulation mutations. In addition, we measured appearance auxotrophs, which allowed us calculate average spontaneous rate approximately 0.3-1.5 x 10(-9) per base pair generation. This is largest target studied so far, collection about 200 genes.