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

¹ University of Pittsburgh

^* To whom correspondence should be addressed. E-mail: xlwu{at}pitt.edu.

Submitted on September 12, 2007
Revised on October 22, 2007
Accepted on 14 January 2008

	Abstract

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 subject 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.

Key Words: ecology, epigenetics, flow cytometry, lambda phage, persistence, receptor adsorption