The massive use of antibiotics in human health and animal breeding has led to the selection of bacteria resistant to antibiotics, a phenomenon representing nowadays one of the most important concern in infectious desease management. Biological control, i.e. the control of a pest by the introduction of a natural enemy or predator/parasite, represents an alternative strategy to the use of antibiotics. The main advantage of biocontrol is that contrary to antibiotics, the pest enemy can counteradapt to resistant mutant and kill them. In evolutionary ecology, such adaptation and counteradaptation cycles are described as "antagonistic coevolutionary interactions". Even if the biocontrol strategy is promising, not much is known about antagonistic coevolution. For instance, the impact of environmental factors like disturbances (a temporary change in environmental conditions causing massive population size reductions) on antagonistic coevolution, remains a complete mystery.

During my PhD, I studied these phenomena by setting up a new biological model with the bacteria Bdellovibrio bacteriovorus - Pseudomonas fluorescens. Using this system, I performed a long-term evolution experiment for more than 300 generations, in which both organims were cocultured under 6 different environmental conditions. In a first article (Gallet et al. 2007), I showed the importance of environmental disturbance on the maintenance of prey diversity, and demonstrated in a second article (Gallet et al. 2009), that antagonistic coevolution between prey and predators, occured only in specific disturbance conditions and with a specific prey genotype.

With the help of JM Ghigo at the Pasteur Institute, I tested the effect of B. bacteriovorus on E. coli or P. fluorescens biofilms using microfermenters. Even if the predator population could be maintained under the chemostat-growing conditions, we failed to detect a significant effect of the predator on prey population sizes.

Overall, these results showed that B. bacteriovorus can efficiently be used as a biocontrol agent only in specific environmental conditions. Today, this bacterial predator is used in the fish farming industry.

Keywords: Host–parasite interaction, predator–prey interaction, antagonistic coevolution, Arms race, Red Queen theory, evolution of life history traits, adsorption rate, Bdellovibrio bacteriovorus, Pseudomonas fluorescens, bacteriophage Lambda, Escherichia coli, adaptation.