The rate of T7 phage-mediated lysis of Escherichia coli growing in exponential phase is not affected by deletion of rpoS

Abstract

RpoS is an Escherichia coli sigma factor shown to regulate genes in response to various environmental and internal stressors. Previous studies have investigated the role of RpoS in a mechanism known as a cross-protection, in which prior exposure to one stressor leads to increased tolerance to a subsequent stressor. Pre-treatment with subinhibitory levels of antibiotics have been used in several studies in an attempt to elicit a delay in phage-lysis, with varying and contradicting results. We propose that the delayed T7-mediated lysis phenotype may be growth phase dependent as the stress response sigma factor RpoS is known to be expressed in stationary phase. Here, we attempted to perform phage lysis assays on wild-type (WT) and rpoS knockout strains of Escherichia coli strains growing in stationary and exponential phase, to look for differences in the time to observe bacteriophage-mediated lysis. We did not observe differences in the time of phage-mediated lysis between wild type and rpoS knock-out strains of E. coli growing in exponential phase. An attempt was made to compare phage-mediated lysis time of E. coli grown in exponential and stationary phase, however, technical issues related to normalizing optical density prevented meaningful comparisons. In conclusion, our study characterizes the E. coli rpoS knock-out strain JW5437-1 at the nucleotide level, compares the growth curves of a wild type and rpoS knock-out strain of E. coli, and shows that phage-mediated lysis times are not different between these strains when growing in exponential phase, which suggests RpoS plays no role in this phase.