Scientists at Arizona State University have identified two unexpected ways bacteria can spread without their usual flagella structures. In one study, E. coli and salmonella use sugar fermentation to create fluid currents for surface migration, dubbed 'swashing.' A separate study reveals a molecular 'gearbox' in flavobacteria that controls directional movement.
New research from Arizona State University demonstrates that bacteria possess alternative propulsion methods beyond their typical flagella, which are whip-like structures that normally enable movement. These findings highlight the adaptability of microbes in spreading across surfaces, with potential implications for infection control.
In the first study, led by Navish Wadhwa from the Biodesign Center for Mechanisms of Evolution and the Department of Physics at ASU, researchers examined E. coli and salmonella. Even with flagella disabled, these bacteria migrated across moist surfaces by fermenting sugars such as glucose, maltose, or xylose. This process releases acidic byproducts like acetate and formate, generating tiny outward fluid currents that propel the bacterial colony, a phenomenon named 'swashing.' The study, published in the Journal of Bacteriology and selected as an Editor's Pick, showed that swashing requires fermentable sugars and can be halted by surfactants, unlike flagella-powered swarming.
Wadhwa noted, "We were amazed by the ability of these bacteria to migrate across surfaces without functional flagella. In fact, our collaborators originally designed this experiment as a 'negative control,' meaning that we expected (once rendered) flagella-less, the cells to not move." He added, "But the bacteria migrated with abandon, as if nothing were amiss, setting us off on a multiyear quest to understand how they were doing it."
This mechanism could explain bacterial colonization of medical devices, wounds, food equipment, and body sites like mucus or the urinary tract, where sugar-rich, moist environments prevail. Adjusting factors like pH or sugar levels might limit such spread.
The second study focused on flavobacteria, which glide using the type 9 secretion system (T9SS), a molecular conveyor belt resembling a snowmobile. A protein called GldJ acts as a gear shifter, reversing motor direction from counterclockwise to clockwise when altered, allowing precise navigation. Published in mBio, the research was conducted by Shrivastava from the Biodesign Center for Fundamental and Applied Microbiomics, Biodesign Center for Mechanisms of Evolution, and ASU's School of Life Sciences.
Shrivastava stated, "We are very excited to have discovered an extraordinary dual-role nanogear system that integrates a feedback mechanism, revealing a controllable biological snowmobile and showing how bacteria precisely tune motility and secretion in dynamic environments."
The T9SS influences health variably: in the oral microbiome, it links to gum disease, inflammation, heart disease, and Alzheimer's; in the gut, it protects antibodies, aiding immune defenses and vaccines. Both studies underscore the need for strategies targeting metabolism or molecular systems, beyond just flagella, to curb infections and biofilms.
