Roughgarden Joan
Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, HI 96744, USA.
Department of Biology, Stanford University, Stanford, CA 94305, USA.
Virus Evol. 2024 Apr 3;10(1):veae028. doi: 10.1093/ve/veae028. eCollection 2024.
The transition between lytic and lysogenic life cycles is the most important feature of the life-history of temperate viruses. To explain this transition, an optimal life-history model is offered based a discrete-time formulation of phage/bacteria population dynamics that features infection of bacteria by Poisson sampling of virions from the environment. The time step is the viral latency period. In this model, density-dependent viral absorption onto the bacterial surface produces virus/bacteria coexistence and density dependence in bacterial growth is not needed. The formula for the transition between lytic and lysogenic phases is termed the 'fitness switch'. According to the model, the virus switches from lytic to lysogenic when its population grows faster as prophage than as virions produced by lysis of the infected cells, and conversely for the switch from lysogenic to lytic. A prophage that benefits the bacterium it infects automatically incurs lower fitness upon exiting the bacterial genome, resulting in its becoming locked into the bacterial genome in what is termed here as a 'prophage lock'. The fitness switch qualitatively predicts the ecogeographic rule that environmental enrichment leads to microbialization with a concomitant increase in lysogeny, fluctuating environmental conditions promote virus-mediated horizontal gene transfer, and prophage-containing bacteria can integrate into the microbiome of a eukaryotic host forming a functionally integrated tripartite holobiont. These predictions accord more with the 'Piggyback-the-Winner' hypothesis than with the 'Kill-the-Winner' hypothesis in virus ecology.
裂解性生命周期和溶原性生命周期之间的转变是温和噬菌体生命周期中最重要的特征。为了解释这种转变，基于噬菌体/细菌种群动态的离散时间公式提出了一个最优生命周期模型，该模型的特点是通过从环境中对病毒粒子进行泊松抽样来感染细菌。时间步长为病毒潜伏期。在这个模型中，病毒在细菌表面的密度依赖性吸附导致病毒/细菌共存，并且不需要细菌生长中的密度依赖性。裂解期和溶原期之间转变的公式被称为“适应性开关”。根据该模型，当病毒种群作为前噬菌体生长比作为被感染细胞裂解产生的病毒粒子生长更快时，病毒从裂解性转变为溶原性，反之亦然。一个对其感染的细菌有益的前噬菌体在离开细菌基因组时会自动导致较低的适应性，从而导致其被锁定在细菌基因组中，在此被称为“前噬菌体锁定”。适应性开关定性地预测了生态地理规律，即环境富集导致微生物化并伴随着溶原性增加，波动的环境条件促进病毒介导的水平基因转移，并且含有前噬菌体的细菌可以整合到真核宿主的微生物组中形成功能整合的三方共生体。这些预测在病毒生态学中更符合“搭赢家便车”假说，而不是“杀死赢家”假说。
