Novel pathway directed by σ E to cause cell lysis in Escherichia coli.

A large number of Escherichia coli cells become viable but nonculturable at early stationary phase, most of which are directed to lysis in cells with an enhanced active σ(E) level. In this study, we examined the effect of small noncoding RNAs, MicA and RybB, as σ(E) regulon as well as regulators of outer membrane protein (Omp) genes, on the lysis process. micA- and rybB-disrupted mutations almost completely suppressed the cell lysis. Increased expression of micA and rybB or disrupted mutation of ompA, ompC and ompW led to a significant level of cell lysis. The suppression by Mg(2+) was found to maintain the integrity of the Omp-repressed outer membrane. Taken together, the results suggest that the cell lysis proceeds in the cascade of σ(E) → expression of micA and rybB → reduction in Omp proteins → disintegration of the outer membrane.