Prochlorococcus cells are the numerically dominant phototrophs in the open ocean. Cyanophages that infect them are a notable fraction of the total viral population in the euphotic zone, and, as vehicles of horizontal gene transfer, appear to drive their evolution. Here we examine the propensity of three cyanophages—a podovirus, a siphovirus, and a myovirus—to mispackage host DNA in their capsids while infecting Prochlorococcus, the first step in phage-mediated horizontal gene transfer. We find the mispackaging frequencies are distinctly different among the three phages. Myoviruses mispackage host DNA at low and seemingly fixed frequencies, while podo- and siphoviruses vary in their mispackaging frequencies by orders of magnitude depending on growth light intensity. We link this difference to the concentration of intracellular reactive oxygen species and protein synthesis rates, both parameters increasing in response to higher light intensity. Based on our findings, we propose a model of mispackaging frequency determined by the imbalance between the production of capsids and the number of phage genome copies during infection: when protein synthesis rate increase to levels that the phage cannot regulate, they lead to an accumulation of empty capsids, in turn triggering more frequent host DNA mispackaging errors.

原绿球藻细胞是开放海洋中数量占优势的光养生物。感染它们的噬藻体占真光带病毒总数的显着比例，并且作为水平基因转移的载体，似乎推动了它们的进化。在这里，我们检查了三种蓝噬菌体（足病毒、管病毒和肌病毒）在感染原绿球藻时将宿主 DNA 错误包装在其衣壳中的倾向，这是噬菌体介导的水平基因转移的第一步。我们发现三种噬菌体的错误包装频率明显不同。肌病毒以低且看似固定的频率错误包装宿主DNA，而足病毒和管状病毒的错误包装频率根据生长光强度而变化几个数量级。我们将这种差异与细胞内活性氧的浓度和蛋白质合成率联系起来，这两个参数都会随着更高的光强度而增加。根据我们的发现，我们提出了一个错误包装频率模型，该模型由感染过程中衣壳的产生与噬菌体基因组拷贝数之间的不平衡决定：当蛋白质合成率增加到噬菌体无法调节的水平时，它们会导致空衣壳，进而引发更频繁的宿主 DNA 错误包装错误。