Outer Membrane Porin F in E. coli Is Critical for Effective Predation by Bdellovibrio .

Bdellovibrio and like organisms (BALOs) are a unique bacterial group that live by predating on other bacteria, consuming them from within to grow and replicate before the progeny come out to complete the life cycle. The mechanisms by which these predators recognize their prey and differentiate them from nonprey bacteria, however, are still not clear. Through genetic knockout and complementation studies in different Escherichia coli strains, we found that Bdellovibrio bacteriovorus strain 109J recognizes outer membrane porin F (OmpF) on the E. coli surface and that the activity of the E. coli EnvZ-OmpR regulatory system significantly impacts predation kinetics. OmpF is not the only signal by which BALOs recognize their prey, however, as B. bacteriovorus could eventually predate on the E. coli ΔompF mutant after prolonged incubation. Furthermore, recognizing OmpF as a prey surface structure was dependent on the prey strain, as knocking out OmpF protein homologues in other prey species, including Escherichia fergusonii, Klebsiella pneumoniae, and Salmonella enterica, did not always reduce the predation rate. Consequently, although OmpF was found to be an important surface component used by Bdellovibrio to efficiently recognize and attack E. coli, future work is needed to determine what other prey surface structures are recognized by these predators. IMPORTANCE Bdellovibrio bacteriovorus and like organisms (BALOs) are Gram-negative predatory bacteria that attack other Gram-negative bacteria by penetrating their periplasm and consuming them from within to obtain the nutrients necessary for the predator's growth and replication. How these predators recognize their prey, however, has remained a mystery. Here, we show that the outer membrane porin F (OmpF) in E. coli is recognized by B. bacteriovorus strain 109J and that the loss of this protein leads to severely delayed predation. However, predation of several other prey species was not dependent on the recognition of this protein or its homologues, indicating that there are other structures recognized by the predators on the prey surface that are yet to be discovered.