How Bacteria Survive Eukaryotic Predation

Abstract

For over a billion years, single-celled amoebae have hunted bacteria in soil and water. Only bacteria that could kill, evade, or outlast these predators survived to reproduce. Yet little is known about how they do it, largely because bacterial genetics has been studied without predators present. This project, initially inspired by a large-scale science education program, opens a new discovery frontier by empowering evolution to do the work. We will grow populations of a common soil bacterium that is related to opportunistic pathogens, Pseudomonas fluorescens, under active predation by the amoeba Dictyostelium discoideum. Using genetic barcodes, we can track hundreds of bacterial lineages at once as they evolve. This will reveal, in real time, the mutations and strategies that let bacteria escape, repel, or outlast being eaten, and how well each defense works. Surprisingly, we discovered that some bacteria survive better in mixed populations than any single type does alone. This points to a collective, population-level survival strategy rather than one confined to individual bacteria. We will also test these defenses against amoebae with specific sensory or feeding deficits to map which bacterial strategy defeats which predatory tool. Just as bacteria may cooperate against a predator, we will evaluate whether wild amoeba strains can team to overcome acquired bacterial defenses. The broad significance of this work stems from the fact that the cellular machinery amoebae use to engulf and kill bacteria closely resembles the machinery of our own immune cells. A defense that lets bacteria survive amoebae may be the same trick a future pathogen uses to evade the human immune system. This work will build a large-scale, unbiased map of how bacteria defend against a eukaryotic predator. It promises fundamental insight into microbial evolution and a new lens on how emerging pathogens acquire their abilities to combat eukaryotic cells.

Back to New Initiative Grants