Convergent evolution toward an improved growth rate and a reduced resistance range in Prochlorococcus strains resistant to phage
Convergent evolution toward an improved growth rate and a reduced resistance range in Prochlorococcus strains resistant to phage
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DOI：
10.1073/pnas.1420347112
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发表时间：
2015-04-28
影响因子：
11.1
通讯作者：
Lindell, Debbie
中科院分区：
文献类型：
--
作者：
Avrani, Sarit;Lindell, Debbie
原绿球藻是一种丰富的海洋蓝藻，在环境中生长迅速，对全球初级生产有重要贡献。这种蓝细菌与海洋中的许多噬藻体共存，可能是由于对许多共同发生的细菌的抗性。原绿球藻中经常发生自发性抗性，并且通常伴随着多效性适合度代价，表现为生长速率降低或被其他细菌感染增强。在这里，我们评估了一些抗噬菌体原绿球藻菌株的命运，重点是那些具有高健身成本。我们发现，噬菌体耐药菌株继续朝着提高生长速度和更窄的耐药范围发展，导致谱系的表型介于祖先易感野生型和初始耐药亚株之间。生长速率和抗性范围的变化往往发生在独立的事件，导致这些表型上的选择压力脱钩。这些变化在很大程度上是位于基因组岛的非核心基因的额外补偿突变的结果，尽管也观察到遗传逆转。此外，还鉴定了一种突变株。多个独立抗性培养物和克隆遵循的进化途径的相似性表明它们经历了可预测的进化途径。这一过程有助于增加原绿球藻种群的遗传多样性和感染排列，进一步增加原绿球藻与其寄生虫之间相互作用网络的复杂性。最后，我们的研究结果为自然界中大量耐药原绿球藻细胞的明显矛盾提供了解释，这些细胞的生长速度接近其最大内在生长率。
Prochlorococcus is an abundant marine cyanobacterium that grows rapidly in the environment and contributes significantly to global primary production. This cyanobacterium coexists with many cyanophages in the oceans, likely aided by resistance to numerous co-occurring phages. Spontaneous resistance occurs frequently in Prochlorococcus and is often accompanied by a pleiotropic fitness cost manifested as either a reduced growth rate or enhanced infection by other phages. Here, we assessed the fate of a number of phage-resistant Prochlorococcus strains, focusing on those with a high fitness cost. We found that phage-resistant strains continued evolving toward an improved growth rate and a narrower resistance range, resulting in lineages with phenotypes intermediate between those of ancestral susceptible wild-type and initial resistant substrains. Changes in growth rate and resistance range often occurred in independent events, leading to a decoupling of the selection pressures acting on these phenotypes. These changes were largely the result of additional, compensatory mutations in noncore genes located in genomic islands, although genetic reversions were also observed. Additionally, a mutator strain was identified. The similarity of the evolutionary pathway followed by multiple independent resistant cultures and clones suggests they undergo a predictable evolutionary pathway. This process serves to increase both genetic diversity and infection permutations in Prochlorococcus populations, further augmenting the complexity of the interaction network between Prochlorococcus and its phages in nature. Last, our findings provide an explanation for the apparent paradox of a multitude of resistant Prochlorococcus cells in nature that are growing close to their maximal intrinsic growth rates.