Escherichia coli responds to nutrient exhaustion by entering a state commonly referred to as the stationary phase. Cells entering the stationary phase redirect metabolic circuits to scavenge any available nutrients and become resistant to different stresses. However, many DNA repair pathways are downregulated in stationary-phase cells, which results in increased mutation rates. DNA repair activity generally depends on consumption of energy and often requires de novo proteins synthesis. Consequently, unless stringently regulated during stationary phase, DNA repair activities may lead to an irreversible depletion of energy sources and, therefore to cell death. Most stationary phase morphological and physiological modifications are regulated by an alternative RNA polymerase sigma factor RpoS. However, nutrient availability, and the frequency and nature of stresses, are different in distinct environmental niches, which impose conflicting choices that result in selection of the loss or of the modification of RpoS function. Consequently, DNA repair activity, which is partially controlled by RpoS, is differently modulated in different environments. This results in the variable mutation rates among different E. coli ecotypes. Hence, the polymorphism of mutation rates in natural E. coli populations can be viewed as a byproduct of the selection for improved fitness.

中文翻译：

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大肠杆菌固定相期间DNA修复活性调节的原因和后果。

大肠杆菌通过进入通常称为固定期的状态来对养分耗尽做出反应。进入固定相的细胞使新陈代谢回路重新定向，以清除任何可用的营养物，并对不同的压力产生抵抗力。但是，许多DNA修复途径在固定相细胞中均被下调，这导致突变率增加。DNA修复活性通常取决于能量的消耗，通常需要从头合成蛋白质。因此，除非在固定阶段进行严格的调节，否则DNA修复活动可能会导致能量的不可逆耗竭，从而导致细胞死亡。大多数固定相的形态和生理修饰均受另一种RNA聚合酶σ因子RpoS的调控。但是，养分的供应 压力的频率和性质在不同的环境利基中是不同的，这些环境会施加冲突的选择，从而导致选择损失或修改RpoS功能。因此，由RpoS部分控制的DNA修复活性在不同的环境中受到不同的调节。这导致不同大肠杆菌生态型之间的可变突变率不同。因此，天然大肠杆菌种群中突变率的多态性可以被视为选择的副产品，以提高适应性。这导致不同大肠杆菌生态型之间的可变突变率不同。因此，天然大肠杆菌种群中突变率的多态性可以被视为选择的副产品，以提高适应性。这导致不同大肠杆菌生态型之间的可变突变率不同。因此，天然大肠杆菌种群中突变率的多态性可被视为选择的副产品，以提高适应性。