Bacteria, much like other creatures, have evolved ingenious methods of navigation. While traversing open water can be straightforward, maneuvering through confined spaces presents unique challenges. Recent research from the University of Chicago reveals that a diverse group of bacteria employs the same basic movements to navigate a variety of environments, from open fluids to densely packed soil and tissues.
The study, led by Jasmine Nirody, PhD, Assistant Professor of Organismal Biology and Anatomy, and published in the journal PRX Life, highlights that bacteria do not alter their movement strategy despite environmental complexity. “We’ve been studying this very prevalent ‘run-and-tumble’ mode of motility for years, but in a very artificial environment. What happens when we introduce things that bacteria would encounter in the real world?” Nirody questioned.
Understanding Bacterial Movement: ‘Run-and-tumble’ vs ‘Hop-and-trap’
Common bacteria such as Salmonella and E. coli use their flagella to propel themselves, employing a movement pattern known as “run-and-tumble.” This involves swimming forward in one direction (“run”) and then stopping to reorient (“tumble”). While effective in open spaces, this movement adapts in confined environments.
In 2019, Princeton researchers identified a movement pattern called “hop-and-trap” in E. coli navigating dense hydrogels. Here, bacteria become trapped by obstacles before reorienting and hopping through openings. Nirody’s team sought to determine if this was a new behavior or a variation of run-and-tumble.
Microfluidic Experiments Reveal Insights
To explore this, the team created a microfluidic device to track E. coli in environments of varying complexity. These devices, typically used to monitor fluid flow, were adapted with pillars to simulate real-world obstacles like soil. In open spaces, bacteria exhibited the expected run-and-tumble motion. However, in confined spaces, their runs shortened upon encountering pillars, and tumbling times increased as they reoriented.
The researchers termed this behavior “swim-and-stall.” Despite appearing different, it was essentially the same run-and-tumble pattern, altered by environmental constraints. Mathematical simulations confirmed that bacteria maintained the same movement strategy across environments.
“It’s doing the same basic thing. It’s not changing the rate that it tumbles or even changing the length of time that it’s running. It’s just failing to succeed,” Nirody explained.
Evolutionary Efficiency: A Single Strategy Across Environments
The findings suggest an evolutionary advantage in maintaining a single movement strategy. Developing distinct methods for different environments would be complex and costly for simple organisms like bacteria. Instead, bacteria have evolved a method that is sufficiently effective across diverse conditions.
“If they have to use a different genetic program that changes how often they tumble in a different environment, or if they constantly have to sense and respond, that can be very costly. But if they develop a baseline that works pretty well across all environments, that’s just much cheaper to do,” Nirody noted.
“Bacteria that live in environments where they’re constantly facing these changes picked a thing that is just good enough for everything, rather than optimizing,” she added.
Implications and Future Research
The study, “Bacterial Motility Patterns Vary Smoothly with Spatial Confinement and Disorder,” was supported by several foundations including the National Science Foundation and the Simons Foundation. It involved contributions from researchers at the University of Chicago, Georgia Institute of Technology, Cornell University, Princeton University, and Northwestern University.
This research not only enhances our understanding of bacterial behavior but also has implications for fields ranging from microbiology to materials science. Future studies may delve deeper into how these movement patterns influence bacterial survival and adaptation in various ecosystems.
As scientists continue to unravel the complexities of bacterial motility, these insights could inform the development of new technologies and strategies for managing bacterial populations in medical and environmental contexts.
