Collective behavior and nongenetic inheritance allow bacterial populations to adapt to changing environments.
Collective behavior and nongenetic inheritance allow bacterial populations to adapt to changing environments.
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DOI：
10.1073/pnas.2117377119
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发表时间：
2022-06-28
影响因子：
11.1
通讯作者：
中科院分区：
文献类型：
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自然选择使种群具有最适应的表型。但集体行为也可以塑造种群的表型构成，即使没有选择。我们在细菌集体迁移的背景下研究这一点，在集体迁移的背景下，个体的趋化能力决定了哪些个体跟上了迁徙的群体。由于这种空间组织是依赖于环境的，我们发现，低表现表型的缓慢丧失使同基因群体能够非遗传地调整其表型组成，以在变化的环境中迁移。这一适应战略的一个重要部分是产生具有新表型的个体的时间尺度。非遗传遗传提供了一种调整这种时间尺度的方法，可能在微生物中广泛存在。集体行为需要一群个人之间的协调。因此，与群体其他成员表型差异太大的个体可能会被排除在外，减少异质性，但增加协调性。如果个体也繁殖，后代的表型可能与父母不同(S)。这就提出了一个问题，即这两个相反的过程--通过集体行为失去多样性和通过增长和遗传产生多样性--如何动态地塑造同基因种群的表型组成。我们使用趋化性细菌的集体迁移作为模型系统，从理论上研究这个问题，不同游泳表型的细胞更适合在不同的环境中导航。我们发现，集体迁徙造成的表型差异损失与环境有关。随着细胞的生长，这种差异损失使迁徙种群能够动态地调整其表型组成以适应环境，促进在多种环境中的迁移。细胞分裂时产生的表型取决于非遗传遗传的水平，较高的遗传导致更大的成分适应和更快的稳态迁移。然而，这是以对新环境的响应速度较慢为代价的。由于这种权衡，有一个最佳的遗传水平，通过变化的环境最大限度地提高迁移速度，使多样化的种群表现优于非多样性的种群。不断增长的种群可能通常会利用集体行为提供的类似选择的效应来动态地塑造自己的表型组成，而不会发生突变。
Natural selection enriches a population with the best-adapted phenotypes. But collective behaviors can also shape a population’s phenotype composition, even without selection. We study this in the context of collective migration of bacteria, in which the spatial arrangement of individuals by their chemotaxis abilities determines which individuals keep up with the migrating group. Since this spatial organization is environment-dependent, we find that a slow loss of low-performing phenotypes enables an isogenic population to nongenetically adapt its phenotype composition to migrate in changing environments. An important part of this adaptation strategy is the time scale on which individuals with new phenotypes are produced. Nongenetic inheritance provides a way to tune this time scale and may be widespread among microbes. Collective behaviors require coordination among a group of individuals. As a result, individuals that are too phenotypically different from the rest of the group can be left out, reducing heterogeneity, but increasing coordination. If individuals also reproduce, the offspring can have different phenotypes from their parent(s). This raises the question of how these two opposing processes—loss of diversity by collective behaviors and generation of it through growth and inheritance—dynamically shape the phenotypic composition of an isogenic population. We examine this question theoretically using collective migration of chemotactic bacteria as a model system, where cells of different swimming phenotypes are better suited to navigate in different environments. We find that the differential loss of phenotypes caused by collective migration is environment-dependent. With cell growth, this differential loss enables migrating populations to dynamically adapt their phenotype compositions to the environment, enhancing migration through multiple environments. Which phenotypes are produced upon cell division depends on the level of nongenetic inheritance, and higher inheritance leads to larger composition adaptation and faster migration at steady state. However, this comes at the cost of slower responses to new environments. Due to this trade-off, there is an optimal level of inheritance that maximizes migration speed through changing environments, which enables a diverse population to outperform a nondiverse one. Growing populations might generally leverage the selection-like effects provided by collective behaviors to dynamically shape their own phenotype compositions, without mutations.
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