Institute of Science and Technology Austria, Am Campus 1, Klosterneuburg, Austria.
Zurich University of Applied Sciences, Campus Grüental, Wädenswil, Switzerland.
Nat Ecol Evol. 2018 Feb;2(2):359-366. doi: 10.1038/s41559-017-0424-z. Epub 2018 Jan 8.
Temperate bacteriophages integrate in bacterial genomes as prophages and represent an important source of genetic variation for bacterial evolution, frequently transmitting fitness-augmenting genes such as toxins responsible for virulence of major pathogens. However, only a fraction of bacteriophage infections are lysogenic and lead to prophage acquisition, whereas the majority are lytic and kill the infected bacteria. Unless able to discriminate lytic from lysogenic infections, mechanisms of immunity to bacteriophages are expected to act as a double-edged sword and increase the odds of survival at the cost of depriving bacteria of potentially beneficial prophages. We show that although restriction-modification systems as mechanisms of innate immunity prevent both lytic and lysogenic infections indiscriminately in individual bacteria, they increase the number of prophage-acquiring individuals at the population level. We find that this counterintuitive result is a consequence of phage-host population dynamics, in which restriction-modification systems delay infection onset until bacteria reach densities at which the probability of lysogeny increases. These results underscore the importance of population-level dynamics as a key factor modulating costs and benefits of immunity to temperate bacteriophages.
温和噬菌体作为原噬菌体整合到细菌基因组中，是细菌进化过程中遗传变异的重要来源，它们经常传播有助于增强适应性的基因，如导致主要病原体毒力的毒素。然而，只有一小部分噬菌体感染呈溶原性并导致原噬菌体的获得，而大多数则呈裂解性并杀死受感染的细菌。除非能够区分裂解性感染和溶原性感染，否则针对噬菌体的免疫机制预计将成为一把双刃剑，以牺牲细菌获得潜在有益原噬菌体的机会为代价，增加其存活的几率。我们表明，尽管限制修饰系统作为先天免疫的机制在个体细菌中不加区分地防止裂解性感染和溶原性感染，但它们会增加在群体水平上获得原噬菌体的个体数量。我们发现，这种违反直觉的结果是噬菌体-宿主群体动态的结果，其中限制修饰系统延迟感染的发生，直到细菌达到溶原性增加的密度。这些结果强调了群体水平动态作为调节针对温和噬菌体的免疫成本和收益的关键因素的重要性。
