Study shows how self-swimming microorganisms get by in harsher conditions

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• Source: Springer


• Date: 18 Mar,2021

Many bacteria swim towards nutrients by rotating the helix-shaped flagella attached to their bodies. As they proceed, the cells may either’run’ in a straight line, or’fall’ by varying the rotational directions of the flagella, inducing their avenues to intentionally alter course.

Through a process named’chemotaxis,’ bacteria can decrease their rate of tumbling at higher levels of nutrients, while maintaining their swimming speeds. In more hospitable environments like the gut, this permits them to seek out nutrients more easily.

But in more nutrient-sparse surroundings, some species of bacteria will also function’chemokinesis’: increasing their swim speeds as nutrient concentrations increase, without altering their tumbling rates. Through new research published in EPJ E, Theresa Jakuszeit and a group at the University of Cambridge led by Ottavio Croze produced a model which correctly accounts for the combined influences of these two motions.

The team’s findings deliver new insights into how self-swimming microbes survive, particularly in harsher environments like lands and oceans.

Previously, studies have shown how chemokinesis permits bacteria to band around nutrient sources, react quickly to short bursts of nourishment, and even form mutually beneficial relationships with algae. Up to now, however, none of them have directly measured how bacterial swim speeds can vary with nutrient concentration.

Starting from mathematical equations describing run-and-tumble dynamics, Croze’s team extended a widely used model for chemotaxis to incorporate chemokinesis. They then applied the new model to forecast the dynamics of bacterial populations within the chemical gradients generated by nutrient distributions used in previous experiments.

Through their strategy, the researchers showed numerically how a combination of both motions can improve the responses of populations in comparison with chemotaxis alone. They also presented more precise predictions of how bacteria respond to nutrient distributions – including sources which emit nutrients sporadically. This allowed them to better evaluate the biological benefits of motility.