Modulation of bacterial cell size and growth rate via activation of a cell envelope stress response

Cells mount elaborate responses to environmental stresses across multiple scales. In enterobacteria, the Rcs phosphorelay is activated by cell-envelope damage and by alterations to periplasmic thickness and cell width. To explore Rcs activation in the absence of external stresses, we investigated the physiological and morphological consequences of Rcs activation in Escherichia coli. We used an inducible variant of the lipoprotein RcsF that mislocalizes to the inner membrane (RcsF^IM) and constitutively activates the Rcs system. RcsF^IM expression slowed growth and reduced the cell length added per cell cycle, independent of Rcs-regulated capsule production. Concurrently, the concentration of the division protein FtsZ increased, and division rings formed closer together in filamentous cells. Depletion of the Rcs negative regulator IgaA also slowed growth and elevated FtsZ levels, indicating that IgaA is essential due to growth inhibition in its absence. In contrast, treatment with the Rcs-activating antibiotic A22 did not affect growth rate or FtsZ concentration and restored normal growth in cells in which the Rcs system was pre-induced with RcsF^IM expression. Hence, the cellular response to A22 buffers the Rcs-dependent effect on cell growth. Together, our findings suggest that Rcs modulates cell division indirectly through growth-rate changes and that activation of the same pathway in different contexts can produce distinct physiological outcomes.

Bacteria must coordinate their growth rate, shape, and division to survive and flourish, yet how these cellular properties are maintained in the face of environmental stresses is poorly understood. Working with Escherichia coli, we show that activating the Rcs phosphorelay, an envelope stress-signaling system, in the absence of external stresses slows growth, shortens cells, and increases the concentration of the key division protein FtsZ, leading to more closely spaced division sites. Depleting the levels of IgaA, a regulator of the Rcs pathway, yielded similar phenotypes. However, activating Rcs via drug-induced cell-wall disruption did not affect growth rate, indicating that the physiological impact of this pathway depends on the context of activation. Our findings reveal links among cell growth, shape homeostasis, and cell envelope stress. Understanding this coupling further will provide new avenues to predict and modulate bacterial growth and physiology during stress.