Beyond the Propeller: Arizona State University Scientists Discover Bacteria "Swashing" and Shifting Molecular Gears

New research reveals bacteria use "swashing" currents and molecular gearboxes to spread, challenging traditional views on how microbes move and cause infection.

By: AXL Media

Published: Mar 13, 2026, 5:51 PM EDT

Source: Information for this report was sourced from Arizona State University

The traditional understanding of bacterial movement has long centered on the flagellum, a rotating protein tail that propels the cell through liquid. However, new research from Arizona State University demonstrates that common pathogens like E. coli and salmonella can migrate across moist surfaces even when these mechanical propellers are disabled. This newly identified behavior, termed "swashing," allows bacterial colonies to expand by utilizing their own metabolic byproducts. The discovery suggests that many microbes previously thought to be immobile under certain conditions may still possess the capacity to colonize medical environments and human tissue.

The Physics of Sugar Fueled Swashing

The mechanism behind swashing is rooted in the fermentation of sugars such as glucose and maltose. As the bacteria consume these nutrients, they release acidic byproducts, including formate and acetate, into the surrounding thin film of moisture. These chemical changes create outward-flowing fluid currents that physically carry the bacterial cells along the surface. According to Navish Wadhwa, an assistant professor at ASU’s Department of Physics, this process was discovered accidentally during a "negative control" experiment where flagella-less cells were expected to remain stationary but instead migrated aggressively across the testing medium.

Surface Chemistry and Infection Control

The identification of swashing provides a potential explanation for how bacteria colonize medical catheters, implants, and food processing surfaces where traditional swimming is restricted. Environmental factors such as pH levels and sugar concentrations appear to be the primary throttles for this movement. Interestingly, the study found that the application of surfactants completely halted the swashing effect while leaving flagella-powered swarming unaffected. This distinction indicates that the two behaviors rely on entirely different physical principles, suggesting that future sanitation strategies could be tailored based on the specific metabolic state of the contaminating bacteria.

The Microscopic Snowmobile and the GldJ Gearbox