Dudebout, E. M. | Search bioRxiv

bioRxiv2025

Osmotic stress triggers fast and reversible PMF collapse in Escherichia coli

Environmental stressors routinely impact bacteria and affect their physiology. Among the most important physiological parameters is the proton motive force (PMF), that powers vital cellular processes and molecular machines. Measuring how PMF responds to environmental stress in real time requires tools that capture rapid physiological changes with high temporal resolution. Here, we use the bacterial flagella motor as an in vivo voltmeter to probe PMF dynamics during hyperosmotic shock. Because motor rotation frequency scales linearly with PMF, this approach enables single-cell electrophysiology with high temporal resolution. We find that hyperosmotic stress causes a rapid and reversible loss of PMF in Escherichia coli, independent of the osmolyte used or the presence of potassium ions. We corroborate these findings by using the Nernstian dye, tetramethyl rhodamine methyl ester (TMRM), showing that hyperosmotic shock leads to membrane depolarization. Together, our results highlight the efficacy of the flagellar motor as powerful tool for probing bacterial electrophysiology and reveal that hyperosmotic stress directly disrupts cellular energetics in addition to its mechanical effects.

biophysics↗

bioRxiv2024

Surfing Motility: A Novel Propulsion-Independent Mechanism for Surface Migration in Salmonella and E. coli

Bacterial motility over surfaces is crucial for colonization, biofilm formation, and pathogenicity. Surface motility in Escherichia coli and Salmonella enterica is traditionally believed to rely on flagellar propulsion. Here, we report a novel mode of motility, termed "swashing," where these bacteria migrate on agar surfaces without functional flagella. Mutants lacking flagellar filaments and motility proteins exhibit rapid surface migration comparable to wild-type strains. Unlike previously described sliding motility, swashing is inhibited by surfactants and requires fermentable sugars. We propose that the fermentation of sugars at the colony edge produces osmolytes, creating local osmotic gradients that draw water from the agar, forming a fluid bulge that propels the colony forward. Our findings challenge the established view that flagellar propulsion is required for surface motility in E. coli and Salmonella, and highlight the role of a fermentation in facilitating bacterial spreading. This discovery expands our understanding of bacterial motility, offering new insights into bacterial adaptive strategies in diverse environments. Significance StatementBacteria move on surfaces using a variety of mechanisms, with important implications for their growth and survival in both the clinical setting (such as on the surface of medical devices) and in the wild. Surface motility in the medically important model species S. enterica and E. coli has been extensively studied and is thought to require flagellar propulsion. Here, we show surface expansion in these species even in the absence of propulsion by the flagella. Instead, movement is tied to fermentation and surface tension: As cells ferment sugars, they create local osmolarity gradients, which generate a wave of fluid on which the cells "swash."

microbiology↗