Rosche W A, Foster P L
Department of Environmental Health, Boston University School of Public Health, Boston University School of Medicine, Boston, MA 02118, USA.
Proc Natl Acad Sci U S A. 1999 Jun 8;96(12):6862-7. doi: 10.1073/pnas.96.12.6862.
Microbial populations under nonlethal selection can give rise to mutations that relieve the selective pressure, a phenomenon that has come to be called "adaptive mutation." One explanation for adaptive mutation is that a small proportion of the cells experience a period of transient hypermutation, and that these hypermutators account for the mutations that appear. The experiments reported here investigated the contribution that hypermutators make to the mutations occurring in a Lac- strain of Escherichia coli during selection for lactose utilization. A broad mutational screen, loss of motility, was used to compare the frequency of nonselected mutations in starved Lac- cells, in Lac+ revertants, and in Lac+ revertants carrying yet another nonselected mutation. These frequencies allowed us to calculate that the hypermutating subpopulation makes up approximately 0.06% of the population and that its mutation rate is elevated approximately 200-fold. From these numbers we conclude that the hypermutators are responsible for nearly all multiple mutations but produce only approximately 10% of the adaptive Lac+ mutations.
在非致死选择条件下的微生物群体可能会产生能够减轻选择压力的突变，这一现象被称为“适应性突变”。对于适应性突变的一种解释是，一小部分细胞经历一段短暂的高突变期，并且这些高突变体导致了出现的突变。本文报道的实验研究了高突变体对大肠杆菌乳糖利用缺陷型（Lac-）菌株在选择利用乳糖过程中发生的突变所起的作用。通过一个广泛的突变筛选，即运动性丧失，来比较饥饿的Lac-细胞、Lac+回复突变体以及携带另一个非选择突变的Lac+回复突变体中未选择突变的频率。这些频率使我们能够计算出高突变亚群体约占群体的0.06%，并且其突变率提高了约200倍。从这些数据我们得出结论，高突变体几乎导致了所有的多重突变，但仅产生了约10%的适应性Lac+突变。
