A Model for Damage Load and Its Implications for the Evolution of Bacterial Aging
A Model for Damage Load and Its Implications for the Evolution of Bacterial Aging
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DOI：
10.1371/journal.pgen.1001076
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发表时间：
2010-08-01
期刊：
影响因子：
4.5
通讯作者：
Chao, Lin
中科院分区：
文献类型：
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作者：
Chao, Lin
有害的突变在种群中出现的频率增加，直到被自然选择停止。随后的平衡产生了有害突变或突变负荷的稳定频率。在这里，我发展了损伤负荷的可比概念，这是由表型的有害的非遗传性变化引起的。当伤害的增加被选择对抗时，伤害负荷也会增加。损伤载荷的存在有利于母亲向女儿不对称传递损伤的演化。这种不对称性是有益的，因为它增加了适应性方差，但它也会导致衰老或衰老。一个基于微生物的数学模型显示，如果终生损伤率不超过阈值，对称分裂的细胞谱系是不朽的。不对称性的进化允许血统在阈值以上持续存在，但血统变得致命。在具有低基因组突变率的微生物中，损伤负荷可能比突变负荷大得多。在具有较高基因组突变率的后生动物中，损伤和突变负荷可能具有相同的量级。模型与实验数据的拟合表明，大肠杆菌细胞经历的损伤率低于阈值，并且在所研究的条件下是不朽的。该模型估计了E.大肠杆菌是低的，但足以持续在较高的损害率。该模型还预测，增加不对称性会导致适应性收益减少，这可能解释了为什么细菌没有进化出更高的不对称性。
Deleterious mutations appearing in a population increase in frequency until stopped by natural selection. The ensuing equilibrium creates a stable frequency of deleterious mutations or the mutational load. Here I develop the comparable concept of a damage load, which is caused by harmful non-heritable changes to the phenotype. A damage load also ensues when the increase of damage is opposed by selection. The presence of a damage load favors the evolution of asymmetrical transmission of damage by a mother to her daughters. The asymmetry is beneficial because it increases fitness variance, but it also leads to aging or senescence. A mathematical model based on microbes reveals that a cell lineage dividing symmetrically is immortal if lifetime damage rates do not exceed a threshold. The evolution of asymmetry allows the lineage to persist above the threshold, but the lineage becomes mortal. In microbes with low genomic mutation rates, it is likely that the damage load is much greater than the mutational load. In metazoans with higher genomic mutation rates, the damage and the mutational load could be of the same magnitude. A fit of the model to experimental data shows that Escherichia coli cells experience a damage rate that is below the threshold and are immortal under the conditions examined. The model estimates the asymmetry level of E. coli to be low but sufficient for persisting at higher damage rates. The model also predicts that increasing asymmetry results in diminishing fitness returns, which may explain why the bacterium has not evolved higher asymmetry.