How Bacteria Move Without Flagella — New Arizona State Study

Bacteria movement without flagella: how bacteria spread on moist surfaces without propeller-like flagella. This Arizona State University bacteria study on E. coli and salmonella reveals microbial motility without flagella driven by sugar fermentation and a newly identified behavior called “swashing.” Learn how germs move, how bacteria on surfaces can travel faster than diffusion, and what this means for infection control and hygiene. The surprising new ways bacteria spread without propellers, including fermentation-driven swashing and a microscopic molecular “gearbox.” Clear, science-based insights into bacteria movement that help you understand how bacteria spread and how to better manage contamination risks.

What You'll Learn:

• How swashing enables bacteria colonies to spread up to 10× faster than diffusion alone, reaching nearly 1 cm in 24 hours on 0.3% agar.
• Why E. coli and salmonella can still move and expand without flagella, reshaping classic ideas of bacteria movement and microbial motility on surfaces.
• How fermenting sugars generates tiny fluid currents that transport cells, powering microbial motility without flagella on moist surfaces.
• How fluorescent beads are used to measure swashing flow speed, and what peak velocities of ~40 µm s⁻¹ reveal about how fast bacteria can move.
• What genetic knockouts of fliC (flagella) vs. pfkA (sugar fermentation) show about the true drivers of swashing and how germs move without propellers.
• How swashing compares to swarming and other modes of bacterial surface motility, and why moist surface bacteria spread is more complex than simple diffusion.
• What these discoveries mean for bacteria on surfaces in hospitals, kitchens, and food processing facilities, and how they may influence cleaning and disinfection strategies.
• How a newly discovered bacterial molecular “gearbox” allows some microbes to control their motion and adapt to changing environments.

About the Guest:

In this episode, we spotlight scientists from Arizona State University whose research sits at the intersection of microbiology, biophysics, and fluid dynamics. Their work uses genetic knockouts, high-resolution imaging, and particle tracking to uncover hidden modes of bacterial motility, from fermentation-driven swashing to molecular gearboxes that tune microbial movement. These insights directly inform how we understand infection spread, surface contamination, and the behavior of bacteria in real-world environments.

Episode Content:

• 00:00 - Introduction: why bacteria movement without flagella matters
• 04:10 - Classic views of how bacteria spread and the limits of flagella-focused models
• 09:45 - The Arizona State University bacteria study that uncovered swashing
• 15:30 - Using fluorescent beads to track fluid flows and measuring 40 µm s⁻¹ speeds
• 21:05 - Genetic evidence: fliC knockout vs. pfkA knockout and what really powers swashing
• 28:40 - Comparing swashing to swarming and other surface motility behaviors
• 34:15 - From agar to the real world: moist surface bacteria spread on hospital and food-contact surfaces
• 41:20 - The microscopic molecular “gearbox” that lets some bacteria control their movement
• 48:50 - Implications for infection control, food safety, and environmental hygiene
• 55:00 - Key takeaways and future directions in research on how bacteria spread without flagella