Within gamma-proteobacteria such as Escherichia coli, RpoS is the master regulator of the general stress response. The presence of RpoS is thought to be important for the ability of bacteria such as E. coli to cope with stressful conditions such as starvation. Here, we quantified the effect of the loss of RpoS on cell viability following logarithmic growth and increasing periods of stationary growth during starvation. We show that the E. coli lab strain MG1655 carrying RpoS can withstand 24 hours of growth in liquid LB without losing any viability. However, following 48 hours of growth there is massive loss of viability. In contrast rpoS knock out MG1655 loses viability already following 24 hours of growth. This indicates that within the lab strain of E. coli that most often faces cycles of starvation ranging in the area of ~24 hours, RpoS provides 24 hours of protection against loss of viability. We also demonstrate that following starvation, surviving E. coli rpoS knock out mutants present an “injury” phenotype, under which they show a longer lag period prior to initiating growth and produce significantly smaller colonies. We utilized the CRISPR system to conditionally silence RpoS in wild type E. coli. This provided us with evidence indicating that the injury to the starved E. coli lacking RpoS occurs during starvation and is not related to recovery from starvation. We are now investigating the extent to which this injury persists following additional cycles of growth in the absence of starvation.
