[Oscillations in population densities of the bacterial prey-predator couple Escherichia coli-Bdellovibrio bacteriovorus: experimental study and theoretical model].

Oscillations in population densities in the bacterial predator-prey Bdellovibrio bacteriovorus-Escherichia coli system were investigated both experimentally and theoretically. Experimental conditions for observing (damped) oscillations were first determined in a closed system and then used in an open system, i.e. in a chemostat, when an adequate flux of nutritive medium was added. The experimentally observed oscillations were always unstable with poorly reproducible amplitude and period. A theoretical model was used in order to explain this behaviour. It was first presented and satisfactorily tested for the same bacterial couple operating in a closed system, and allowed an experimental determination of its kinetic parameters. When adapted to open system conditions, it yielded computer-simulations which showed oscillations of the population densities in good agreement with those experimentally observed. It also showed that stable oscillations were not possible, the only "focus" in the predator-prey-density plane being an unstable one with no surrounding limit cycle.