Modulation of prey size reveals adaptability and robustness in the cell cycle of an intracellular predator

Despite the remarkable diversity of bacterial lifestyles, the sophisticated regulatory networks underlying bacterial replication have only been investigated in a limited number of model species so far. In bacteria that do not rely on canonical binary division for proliferation, the coordination of major cellular processes is still mysterious. Moreover, bacterial growth and division remain largely unexplored within spatially confined niches where nutrients are limited. This includes the lifecycle of the model endobiotic predatory bacterium Bdellovibrio bacteriovorus, which grows by filamentation within its host or prey cells and produces a variable number of daughter cells. Here, we examined how the size of the micro-compartment in which predators replicate (i.e., the prey bacterium) impacts their cell cycle progression at the single-cell level. Using Escherichia coli with genetically encoded size differences, we show that the duration of the predator cell cycle scales with prey size. As a result, the size of the prey determines the number of predator offspring, through a relationship that is maintained across prey species. Strikingly, the nutritional quality of the prey cell determined the specific growth rate of predators regardless of prey size, reminiscent of the effect of medium composition on the growth of other bacteria. Tuning the predatory cell cycle by modulating prey dimensions also allowed us to reveal invariable temporal connections between key cellular processes. Altogether, our data uncover adaptability and robustness shaping the enclosed replication of B. bacteriovorus. Consequently, predators optimally exploit the finite prey resources and space while ensuring a strict cell cycle progression. This study opens the way to explore diverse cell cycle control strategies by extending their characterization to intracellular lifestyles, beyond canonical models and growth conditions.