Bacterial growth under confinement requires transcriptional adaptation to resist metabolite-induced turgor pressure build-up

Bacterial proliferation often occurs in confined spaces, during biofilm formation, within host cells, or in specific niches during infection, creating mechanical constraints. We investigated how spatial confinement and growth-induced mechanical pressure affect bacterial physiology. Here, we found that, when proliferating in a confining microfluidic-based device with access to nutrients, Escherichia coli cells generate forces in the hundreds of kPa range. This pressure decouples growth and division, producing shorter bacteria with higher protein concentrations. This leads to cytoplasmic crowding, which ultimately arrests division and stalls protein synthesis. In this arrested state, the pressure produced by bacteria keeps increasing. A minimal theoretical model of bacterial growth predicts this novel regime of steady pressure increase in the absence of protein production, that we named overpressurization. In this regime, the Rcs pathway is activated and that abnormal shapes appear in rcs mutant populations only when they reach the overpressurized state. A uropathogenic strain of E. coli displayed the same confined growth phenotypes in vitro and requirement for Rcs in a mice model of urinary tract infection, suggesting that these pressurized regimes are relevant to understand the physiopathology of bacterial infections.