Why E. coli move faster in syrup-like fluids than in water

Why E. coli move faster in syrup-like fluids than in water

Experiments in the 1970s showed that, when in water, E. coli demonstrated what is known as "run and tumble" swimming. A bacterium would swim in a straight line, then tumble, or change direction in a random way. This is a good strategy for finding food, but it was unclear how that strategy would change in the more gelatinous fluids they tend to live in.

The researchers were also able to track individual bacteria, and even single polymer molecules, which when added to water in different amounts, make it more viscous and elastic.

When viscosity increases, E. coli are less able to separate their braid of whip-like flagella. When they rotate together like a propeller, bacteria move forward, but having each rotate in different directions is what allows bacteria to turn. This means they are less likely to tumble when in more viscous fluids.

When elasticity increases, the E. coli's swimming strokes become more efficient. In water, the bacteria tend to wobble, but when surrounded by springy polymers, they become more stable. With individual polymer molecules roughly the same size as a single bacterium, the bacteria's flagella physically stretch out the coiled-up polymers like a rubber band. The force of the polymers pushing back helps the bacteria to swim faster.

http://www.upenn.edu/pennnews/news/penn-researchers-discover-why-e-coli-move-faster-syrup-fluids-water
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