Ecological variation influences the character of many biotic interactions, but examples of predator-prey reversal mediated by abiotic context are few. We show that the temperature at which prey grow before interacting with a predatory bacterial species can determine the very direction of predation, reversing the identities of predator and prey. When lawns of Pseudomonas fluorescens were reared at 32 °C before release of the generalist predator Myxococcus xanthus, M. xanthus extensively killed P. fluorescens. However, when M. xanthus was released onto lawns of P. fluorescens reared at 22 °C, P. fluorescens was the predator, slaughtering M. xanthus to extinction and growing on its remains. Cooler-reared P. fluorescens killed M. xanthus by secreting diffusible molecules that, while lethal to M. xanthus, were benign toward most of several other diverse bacterial species examined. Our results suggest that the sign of predator-prey interactions – and lethal microbial antagonisms more broadly – may often change across abiotic gradients in natural microbial communities, with important ecological and evolutionary implications. They also suggest that a larger proportion of microbial warfare results in predation – the killing and consumption of organisms – than is generally recognized.
