Bishop Amy L, Rab Faiza A, Sumner Edward R, Avery Simon V
School of Biology, Institute of Genetics, University of Nottingham, University Park, Nottingham NG7 2RD, UK.
Mol Microbiol. 2007 Jan;63(2):507-20. doi: 10.1111/j.1365-2958.2006.05504.x. Epub 2006 Dec 14.
Individual cells within isogenic microbial cultures exhibit phenotypic heterogeneity, an issue that is attracting intense interest. Heterogeneity could confer benefits, in generating variant subpopulations that may be better equipped to persist during perturbation. We tested this hypothesis by comparing the survival of wild-type Saccharomyces cerevisiae with that of mutants which are considered stress-sensitive but which, we demonstrate, also have increased heterogeneity. The mutants (e.g. vma3, ctr1, sod1) exhibited the anticipated sensitivities to intermediate doses of nickel, copper, alkaline pH, menadione or paraquat. However, enhanced heterogeneity meant that the resistances of individual mutant cells spanned a broad range, and at high stress occasional-cell survival in most of these populations overtook that of the wild type. Green fluorescent protein (GFP) reporter studies showed that this heterogeneity-dependent advantage was not related to perturbation of buffered gene expression. Deletion strain screens combined with other approaches revealed that vacuolar alkalinization resulting from loss of Vma-dependent vacuolar H(+)-ATPase activity was not the cause of vma mutants' net stress sensitivities. An alternative Vma-dependent resistance mechanism was found to suppress an influence of variable vacuolar pH on the metal resistances of individual wild-type cells. In addition to revealing new mechanisms of heterogeneity generation, the results demonstrate experimentally a benefit under adverse conditions that arises specifically from heterogeneity, and in populations conventionally considered to be disadvantaged.
同基因微生物培养物中的单个细胞表现出表型异质性，这一问题正引起人们的浓厚兴趣。异质性可能带来益处，产生变异的亚群，这些亚群可能更有能力在扰动期间存活下来。我们通过比较野生型酿酒酵母与被认为对压力敏感但我们证明其异质性也增加的突变体的存活率来检验这一假设。这些突变体（如vma3、ctr1、sod1）对中等剂量的镍、铜、碱性pH值、甲萘醌或百草枯表现出预期的敏感性。然而，异质性增强意味着单个突变体细胞的抗性范围很广，在高压力下，这些群体中大多数的偶尔细胞存活率超过了野生型。绿色荧光蛋白（GFP）报告基因研究表明，这种依赖异质性的优势与缓冲基因表达的扰动无关。缺失菌株筛选与其他方法相结合表明，Vma依赖性液泡H(+) - ATP酶活性丧失导致的液泡碱化不是vma突变体净压力敏感性的原因。发现了一种替代的Vma依赖性抗性机制，可抑制可变液泡pH值对单个野生型细胞金属抗性的影响。除了揭示异质性产生的新机制外，结果还通过实验证明了在不利条件下异质性特别产生的益处，以及在传统上被认为处于劣势的群体中的益处。
