The O-antigen mediates differential survival of Salmonella against communities of natural predators.

Antigenically distinct members of bacterial species can be differentially distributed in the environment. Predators known to consume antigenically distinct prey with different efficiencies are also differentially distributed. Here we show that antigenically distinct, but otherwise isogenic and physiologically indistinct, strains of Salmonella enterica show differential survival in natural soil, sediment and intestinal environments, where they would face a community of predators. Decline in overall cell numbers is attenuated by factors that inhibit the action of predators, including heat and antiprotozoal and antihelminthic drugs. Moreover, the fitness of strains facing these predators - calculated by comparing survival with and without treatments attenuating predator activity - varies between environments. These results suggest that relative survival in natural environments is arbitrated by communities of natural predators whose feeding preferences, if not species composition, vary between environments. These data support the hypothesis that survival against natural predators may drive the differential distribution of bacteria among microenvironments.