Data from: Phenotypic stochasticity prevents lytic bacteriophage population from extinction during bacterial stationary phase

It is generally thought that the adsorption rate of a bacteriophage correlates positively with fitness, but this view neglects that most phages rely only on exponentially growing bacteria for productive infections. Thus, phages must cope with the environmental stochasticity that is their hosts’ physiological states. If lysogeny is one alternative, it is unclear how strictly lytic phages can survive the host stationary phase. Three scenarios may explain their maintenance: (1) pseudolysogeny, (2) diversified or (3) conservative bet-hedging. In order to better understand how a strictly lytic phage survives the stationary phase of its host, and how phage adsorption rate impacts this survival, we challenged two strictly lytic phage λ, differing in their adsorption rates, with stationary phase Escherichia coli cells. Our results showed that, pseudolysogeny was not responsible for phage survival and that, contrary to our expectation, high adsorption rate was not more detrimental during stationary phase than low adsorption rate. Interestingly, this last observation was due to the presence of the “residual fraction” (phages exhibiting extremely low adsorption rates), protecting phage populations from extinction. Whether this cryptic phenotypic variation is an adaptation (diversified bet-hedging) or merely reflecting unavoidable defects during protein synthesis remains an open question.

学界普遍认为噬菌体（bacteriophage）的吸附率（adsorption rate）与适合度（fitness）呈正相关，但该观点忽略了多数噬菌体仅能依靠指数生长期细菌完成增殖性感染这一事实。因此，噬菌体必须应对由宿主生理状态带来的环境随机性（environmental stochasticity）。若溶原性（lysogeny）是其中一种生存策略，那么烈性噬菌体（strictly lytic phages）如何在宿主稳定期（stationary phase）存活仍尚不明确。目前有三种假说可解释其种群维持机制：(1) 类溶原性（pseudolysogeny）、(2) 多样化风险分摊（diversified bet-hedging）以及(3) 保守型风险分摊（conservative bet-hedging）。为了更深入地阐明烈性噬菌体如何在宿主稳定期存活，以及噬菌体吸附率对该存活过程的影响，我们以吸附率存在差异的两株烈性λ噬菌体为研究对象，以稳定期大肠杆菌（Escherichia coli）细胞作为宿主开展侵染实验。实验结果显示，类溶原性并非噬菌体存活的关键原因；且与我们的预期相悖，高吸附率在稳定期并未比低吸附率更具劣势。值得注意的是，这一现象源于残留组分（residual fraction）的存在——即吸附率极低的噬菌体亚群——该组分可有效避免噬菌体种群走向灭绝。这种隐蔽表型变异（cryptic phenotypic variation）究竟是一种适应性的多样化风险分摊策略，抑或仅仅是蛋白质合成过程中不可避免的缺陷所导致的结果，仍是一个待解的开放性问题。