Wahl Lindi M, Pattenden Tyler
Applied Mathematics, Western University, London, Ontario N6A 5B7, Canada
Applied Mathematics, Western University, London, Ontario N6A 5B7, Canada.
Genetics. 2017 May;206(1):407-416. doi: 10.1534/genetics.116.197541. Epub 2017 Mar 17.
Prophage sequences constitute a substantial fraction of the temperate virus gene pool. Although subject to mutational decay, prophage sequences can also be an important source of adaptive mutations for these viral populations. Here we develop a life-history model for temperate viruses, including both the virulent (lytic) and the temperate phases of the life cycle. We then examine the survival of mutations that increase fitness during the lytic phase (attachment rate, burst size), increase fitness in the temperate phase (increasing host survival), or affect transitions between the two phases (integration or induction probability). We find that beneficial mutations are much more likely to survive, ultimately, if they first occur in the prophage state. This conclusion applies even to traits that are only expressed during the lytic phase, and arises due to the substantially lower variance in the offspring distribution during the temperate cycle. This observation, however, is balanced by the fact that many more mutations can be generated during lytic replication. Overall we predict that the prophage state provides a refuge, relatively shielded from genetic drift, in which temperate viruses can explore possible adaptive steps.
前噬菌体序列构成了温和病毒基因库的很大一部分。尽管会受到突变衰减的影响，但前噬菌体序列也可能是这些病毒群体适应性突变的重要来源。在此，我们为温和病毒建立了一个生活史模型，包括生命周期中的烈性（裂解）阶段和温和阶段。然后，我们研究了在裂解阶段提高适应性的突变（附着率、爆发大小）、在温和阶段提高适应性的突变（增加宿主存活率）或影响两个阶段之间转换的突变（整合或诱导概率）的存活情况。我们发现，有益突变如果首先以前噬菌体状态出现，最终更有可能存活下来。这一结论甚至适用于仅在裂解阶段表达的性状，并且是由于温和周期中后代分布的方差显著较低而产生的。然而，这一观察结果被裂解复制过程中可以产生更多突变这一事实所平衡。总体而言，我们预测前噬菌体状态提供了一个相对免受遗传漂变影响的避难所，在这个避难所中温和病毒可以探索可能的适应性步骤。
