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首页> 外文期刊>Ecology letters >Death and cannibalism in a seasonal environment facilitate bacterial coexistence
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Death and cannibalism in a seasonal environment facilitate bacterial coexistence

机译：季节性环境中的死亡和食人症促进细菌共存

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Bacterial populations can evolve and adapt to become diverse niche specialists, even in seemingly homogeneous environments. One source of this diversity arises from newly 'constructed' niches that result from the activities of the bacteria themselves. Ecotypes specialized to exploit these distinct niches can subsequently coexist via frequency-dependent interactions. Here, we describe a novel form of niche construction that is based upon differential death and cannibalism, and which evolved during 20 000 generations of experimental evolution in Escherichia coli in a seasonal environment with alternating growth and starvation. In one of 12 populations, two monophyletic ecotypes, S and L, evolved that stably coexist with one another. When grown and then starved in monoculture, the death rate of S exceeds that of L, whereas the reverse is observed in mixed cultures. As shown by experiments and numerical simulations, the competitive advantage of S cells is increased by extending the period of starvation, and this advantage results from their cannibalization of the debris of lysed L cells, which allows the S cells to increase both their growth rate and total cell density. At the molecular level, the polymorphism is associated with divergence in the activity of the alternative sigma factor RpoS, with S cells displaying no detectable activity, while L cells show increased activity relative to the ancestral genotype. Our results extend the repertoire of known cross-feeding mechanisms in microbes to include cannibalism during starvation, and confirm the central roles for niche construction and seasonality in the maintenance of microbial polymorphisms.
机译：细菌种群可以进化并适应成为多样化的利基专家，即使在看似均匀的环境中也是如此。这种多样性的一个来源是由于细菌自身活动而产生的新“构造”的壁arise。专门利用这些独特生态位的生态型可以随后通过频率依赖性相互作用共存。在这里，我们描述了一种新的形式的利基构建，其基于差异性死亡和自相残杀，并且在具有交替生长和饥饿的季节性环境下，在大肠杆菌的2万代实验进化过程中进化。在12个种群中的1个种群中，有两种稳定的并存的单种生态型S和L。当在单培养中生长并饥饿时，S的死亡率超过L的死亡率，而在混合培养中则观察到相反的情况。如实验和数值模拟所示，延长饥饿时间可增加S细胞的竞争优势，而这种优势来自吞噬裂解L细胞碎片的残骸，从而使S细胞既可以提高生长速度，又可以提高总细胞密度。在分子水平上，多态性与替代西格玛因子RpoS的活性差异有关，其中S细胞未显示出可检测的活性，而L细胞相对于祖先基因型则显示出增加的活性。我们的研究结果扩展了微生物中已知的交叉进给机制的范围，使其包括饥饿期间的食人症，并确认了生态位构建和季节性在维持微生物多态性方面的核心作用。

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