Diverse stresses converge on bacterial periplasmic expansion through distinct physiological mechanisms
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Diverse environmental and antibiotic stresses induce localized periplasmic expansion–– the separation of the inner membrane from the cell wall and outer membrane––in Gram-negative bacteria, yet whether these morphologically similar responses arise through a common mechanism remains unclear. Here, we compare periplasmic expansion induced by sudden starvation, ciprofloxacin, mitomycin C, and globomycin in Escherichia coli . We find that these perturbations produce similar morphologies through distinct physiological and mechanical routes. Ciprofloxacin- and mitomycin C-induced periplasmic expansion coincides with loss of turgor, whereas starvation requires water efflux, and globomycin leads to unequal expansion of the inner and outer membrane as a result of aberrant inner membrane–cell wall crosslinking. Outer membrane stiffness modulates expansion during ciprofloxacin treatment. Despite these distinct mechanisms, robust periplasmic expansion during starvation and treatment with ciprofloxacin or globomycin requires UDP-glucose synthesis. Together, these findings establish periplasmic expansion as a convergent physical outcome of diverse stresses and reveal the remarkable plasticity of the Gram-negative cell envelope.
Significance statement
Localized periplasmic expansion is frequently visible in Gram-negative bacteria exposed to diverse stresses, yet it is rarely considered as a biological phenomenon in its own right. Consequently, the mechanisms underlying its formation and its relationship to bacterial physiology remain poorly understood. Here, we show that superficially similar periplasmic expansion can emerge through distinct physiological and mechanical routes during nutrient deprivation and antibiotic stress. Thus, rather than presenting as a single stereotyped stress response, periplasmic expansion is a convergent physical state that can arise from diverse perturbations. Our findings bring attention to a widespread but overlooked bacterial morphology that highlights the periplasm as a dynamic compartment and the Gram-negative cell envelope as a remarkably plastic cellular structure.
