Stochastic receptor expression allows sensitive bacteria to evade phage attack. Part I: Experiments

It has long been suspected that population heterogeneity, either at a genetic level or at a protein level, can improve the fitness of an organism under a variety of environmental stresses. However, quantitative measurements to substantiate such a hypothesis turn out to be rather difficult and have rarely been performed. Herein, we examine the effect of expression heterogeneity of lambda-phage receptors on the response of an Escherichia coli population to attack by a high concentration of lambda-phage. The distribution of the phage receptors in the population was characterized by flow cytometry, and the same bacterial population was then subjected to different phage pressures. We show that a minority population of bacteria that produces the receptor slowly and at low levels determines the long-term survivability of the bacterial population and that phage-resistant mutants can be efficiently isolated only when the persistent phage pressure > 10(10) viruses/cm(3) is present. Below this phage pressure, persistors instead of mutants are dominant in the population.