Decrease in cell viability in an RMF, σ38, and OmpC triple mutant of Escherichiacoli

Abstract In a speG -disrupted Escherichia coli mutant, which cannot metabolize spermidine to acetylspermidine, addition of spermidine to the medium caused a decrease in cell viability at the late stationary phase of growth. There were parallel decreases in the levels of ribosome modulation factor (RMF), the σ 38 subunit of RNA polymerase, and the outer membrane protein C (OmpC). To clarify that these three proteins are strongly involved in cell viability, the rmf , rpoS (encoding σ 38 ), and ompC genes were disrupted. Viability of the triple mutant decreased to less than 1% of normal cells. The triple mutant had a reduced cell viability compared to any combination of double mutants, which also had a reduced cell viability. The single rmf and rpoS , but not ompC , mutant only slightly reduced cell viability. The results indicate that cooperative functions of these three proteins are necessary for cell viability at the late stationary phase. The triple mutant had a reduced level of ribosomes and of intracellular cations.