PHAGE-MEDIATED SELECTION AND THE EVOLUTION AND MAINTENANCE OF RESTRICTION-MODIFICATION
PHAGE-MEDIATED SELECTION AND THE EVOLUTION AND MAINTENANCE OF RESTRICTION-MODIFICATION
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DOI：
10.1111/j.1558-5646.1993.tb02113.x
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发表时间：
1993-04-01
期刊：
影响因子：
3.3
通讯作者：
LEVIN, BR
中科院分区：
文献类型：
--
作者：
KORONA, R;LEVIN, BR
限制性修饰（R-M）的发现是因为它为细菌提供了对噬菌体感染的免疫力。但是，噬菌体介导的选择是负责这些普遍存在的和多重进化系统的进化和维持的唯一机制吗？为了回答这个问题，我们用实验室的E.大肠杆菌和噬菌体以及计算机模拟。我们考虑两种生态情况，其中噬菌体介导的选择可能有利于R-M免疫：i）当细菌与一种新的R-M系统侵入社区的噬菌体敏感的细菌中有一个或多个物种的噬菌体，和ii）当细菌殖民无菌的栖息地中存在的噬菌体。我们的实验结果表明，在已建立的细菌和噬菌体群落中，R-M提供的入侵细菌种群的优势是短暂的。在短时间内，突变体对噬菌体的抗性（抗性）在优势种群中进化，随后在入侵种群中进化。竞争的结果取决于这些细菌克隆的抗性状态的相对适合度，而不是R-M。由于对独立突变体的顺序选择，即使存在两种或三种噬菌体，也会发生这种快速的抗性进化。虽然在我们的实验中，当细菌定植在噬菌体存在的新栖息地时，也会进化出抗性，但新的R-M系统大大增加了它们建立的可能性。我们解释这项研究的结果支持的假设，后者，殖民选择，可能发挥重要作用的进化和维护的限制修改。然而，我们也看到这些结果和我们讨论的其他观察结果，质疑是否对噬菌体的保护是限制修饰的独特生物学作用。
Restriction-modification (R-M) was discovered because it provides bacteria with immunity to phage infection. But, is phage-mediated selection the sole mechanism responsible for the evolution and maintenance of these ubiquitous and multiply evolved systems? In an effort to answer this question, we have performed experiments with laboratory populations of E. coli and phage and computer simulations. We consider two ecological situations whereby phage-mediated selection could favor R-M immunity; i) when bacteria with a novel R-M system invade communities of phage-sensitive bacteria in which there are one or more species of phage, and ii) when bacteria colonize bacterial-free habitats in which phage are present. The results of our experiments indicate that in established communities of bacteria and phage, the advantage R-M provides an invading population of bacteria is ephemeral. Within short order, mutants resistant (refractory) to the phage evolve in the dominant population and subsequently in the invading population. The outcome of competition then depends on the relative fitness of the resistant states of these bacterial clones, rather than R-M. As a consequence of sequential selection for independent mutants, this rapid evolution of resistance occurs even when two and three species of phage are present. While in our experiments resistance also evolved when bacteria colonized new habitats in which phage were present, a novel R-M system greatly augmented the likelihood of their becoming established. We interpret the results of this study as support for the hypothesis that the latter, colonization selection, may play an important role in the evolution and maintenance of restriction-modification. However, we also see these results and other observations we discuss as questioning whether protection against phage is the unique biological role of restriction-modification.