How bacterial predators hunt

A tiny predator implants itself in other bacteria and eats them from the inside. Now researchers know how these hunters find their prey.

The predator bacterium Bdellovibrio bacteriovorus (BV) has the potential to be a living antibiotic, hunting down other bacteria inside the human body. But to make this happen, researchers must first understand how BV identifies its prey. New research sheds light on this 50-year-old mystery. The study shows how fluid forces generated by the bacteria’s own swimming movements help them get closer to their victims. We speak with author Steve Pressé about the findings.

ResearchGate: What is Bdellovibrio bacteriovorus and what’s unique about it?

Steve Pressé: Bdellovibrio bacteriovorus (BV) is a model bacterial predator. Despite having been discovered over 50 years ago, very little is known about how it locates its bacterial prey. Understanding how BV finds its prey is a first step in engineering this bacterium to serve as a living antibiotic, hunting prey inside a living organism.

RG: What does it do to its prey?

Pressé: Much like a virus—and the alien in the Alien movies—it makes its way into its prey and begins replicating by eating away at its prey from the inside. It eventually releases a handful of progeny after a few hours.

RG: What motivated you to investigate how it locates and choses its prey?

Pressé: In past decades, major effort has focused on determining whether BV senses its prey chemically. This is normally the way bacteria sense each other and communicate. Yet all experiments thus far have indicated that BV’s search for prey is not chemical, suggesting that it is random. But it made little sense to us that, after billions of years of evolution, nature would not have identified a better hunting mechanism.

RG: What do your results suggest?

Pressé: What we find instead is that, because the BV moves very fast in solution, it heavily perturbs the fluid around itself. This causes hydrodynamic flows that force predators to change their swimming patterns. This change in swimming patterns forces BV predators into regions where prey is also concentrated for similar reasons, typically surfaces or around defects on surfaces. This allows the predator to reduce its apparently random search for prey, where it would be swimming around searching for its prey in any direction, to a much more efficient search on surfaces or around defects on those surfaces.

RG: How did you determine this?

Pressé: We tracked several hundred bacteria in different environments around and away from specific target regions. We statistically analyzed bacterial tracks in those different environments and under different control settings. We used numerical calculations to show that the behaviors we were observing were all consistent with hydrodynamic effects.

RG: Why is this important to know? 

Pressé: Our findings provide the first steps in understanding how BV hunt, and therefore provide a recipe for modifying BV’s hunting efficiency. With this knowledge, we may now imagine developing BV as a living antibiotic—have it hunt bacterial prey inside a living organism. One might also use it to efficiently degrade bacterial biofilms on surfaces, or even to purify water.

RG: What are the next steps in this research?

Pressé: Our next goal is to engineer efficient hunters and watch them in action inside a living host. While bacterial predators do hunt prey outside living organisms, our conclusions are limited to that context so far. Our results give us clues as to what we should first start looking at when we decide to look into predator-prey dynamics within host organisms.

Featured image: Bdellovibrio bacteriovorus. Credit: NIH