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Stochastic Receptor Expression Allows Sensitive Bacteria to Evade Phage Attack. Part I: Experiments

Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, Pennsylvania

Correspondence: Address reprint requests to X. L. Wu, Physics Dept. of Physics and Astronomy, University of Pittsburgh, 3941 Ohara Street, Pittsburgh, PA 15260. Tel.: 412-624-0873; E-mail: xlwu{at}pitt.edu.

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 -phage receptors on the response of an Escherichia coli population to attack by a high concentration of -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 >10¹⁰ viruses/cm³ is present. Below this phage pressure, persistors instead of mutants are dominant in the population.