Predators have to identify and evaluate their prey before they neutralize and consume them. How these requirements are fulfilled by predatory bacteria is not known. The obligate predatory bacterium Bdellovibrio bacteriovorus’ life cycle entails that cell growth and replication are tied to prey cell consumption. A novel ex vivo cultivation system for B. bacteriovorus enabling growth of the wild type predator in the absence of prey was developed. Using ghost cells, manipulated to bear various contents, we show that spatially and temporally prey-derived signals located in the prey envelope and in the prey soluble fraction are sensed early and late during the interaction, respectively. Their single or combined action leads to a stepwise transition from a motile, free living phase to full-fledged growth through transcriptional effects. This system uncovers a cell cycle checkpoint in which the late signal acts as a determinant of the prey’s nutritional value prior to committing to growth. The interaction is further regulated by a large complement of cyclic di GMP effectors, identified in a pull-down essay. This revealed that stage-specific effectors are integrated in general metabolism as well as in signalling, and bear novel cyclic di-GMP domains. This association between cyclic di GMP signalling, metabolism and cell cycle control will be presented.
