ESI and CEC, Biosciences, University of Exeter , Cornwall Campus, Penryn TR10 9EZ , UK.
Philos Trans R Soc Lond B Biol Sci. 2019 May 13;374(1772):20180098. doi: 10.1098/rstb.2018.0098.
CRISPR-Cas is an adaptive prokaryotic immune system that prevents phage infection. By incorporating phage-derived 'spacer' sequences into CRISPR loci on the host genome, future infections from the same phage genotype can be recognized and the phage genome cleaved. However, the phage can escape CRISPR degradation by mutating the sequence targeted by the spacer, allowing them to re-infect previously CRISPR-immune hosts, and theoretically leading to coevolution. Previous studies have shown that phage can persist over long periods in populations of Streptococcus thermophilus that can acquire CRISPR-Cas immunity, but it has remained less clear whether this coexistence was owing to coevolution, and if so, what type of coevolutionary dynamics were involved. In this study, we performed highly replicated serial transfer experiments over 30 days with S. thermophilus and a lytic phage. Using a combination of phenotypic and genotypic data, we show that CRISPR-mediated resistance and phage infectivity coevolved over time following an arms race dynamic, and that asymmetry between phage infectivity and host resistance within this system eventually causes phage extinction. This work provides further insight into the way CRISPR-Cas systems shape the population and coevolutionary dynamics of bacteria-phage interactions. This article is part of a discussion meeting issue 'The ecology and evolution of prokaryotic CRISPR-Cas adaptive immune systems'.
CRISPR-Cas 是一种适应性的原核免疫防御系统，可防止噬菌体感染。通过将噬菌体衍生的“间隔序列”整合到宿主基因组上的 CRISPR 基因座中，宿主可以识别来自相同噬菌体基因型的未来感染，并切割噬菌体基因组。然而，噬菌体可以通过突变间隔序列靶向的序列来逃避 CRISPR 降解，从而能够重新感染之前具有 CRISPR 免疫的宿主，并在理论上导致共同进化。先前的研究表明，噬菌体可以在能够获得 CRISPR-Cas 免疫的嗜热链球菌种群中长时间存在，但尚不清楚这种共存是否是由于共同进化引起的，如果是，涉及哪些类型的共同进化动态。在这项研究中，我们使用溶菌噬菌体和嗜热链球菌进行了 30 天的高度复制连续传代实验。通过表型和基因型数据的组合，我们表明 CRISPR 介导的抗性和噬菌体感染力随着时间的推移在一场军备竞赛动态中共同进化，并且在这个系统中噬菌体感染力和宿主抗性之间的不对称性最终导致噬菌体灭绝。这项工作进一步深入了解了 CRISPR-Cas 系统如何塑造细菌-噬菌体相互作用的种群和共同进化动态。本文是“原核 CRISPR-Cas 适应性免疫防御系统的生态学和进化”讨论会议的一部分。
