Selection of predation-resistant bacteria in continuous culture

Abstract

VARIOUS models of predator–prey interactions predict the occurrence of reciprocal oscillations in the densities of the predator and its prey¹. Some models predict undamped, neutrally stable oscillations (the Lotka–Volterra model), whereas others predict damped oscillations, the two populations gradually approaching an equilibrium. Few attempts have been made to test these models, possibly because of the rarity of suitable experimental systems. The predatory bacterium Bdellovibrio, which preys on other bacteria, provides an ideal system in which predator–prey interactions can be studied in a convenient and accurate way. As part of a study of the ecology of Bdellovibrio² we have inoculated bdellovibrios into a continuous culture of prey bacteria growing in a chemostat. The introduction of the bdellovibrios was followed by reciprocal population oscillations. However, the oscillations did not persist and were not damped. Instead, a new system evolved in which a bdellovibrio-resistant mutant was detected.