How do bacteria swim

Washington, Nov 20 : A new study from Brown University has shed light on the swimming patterns of bacteria, suggesting that the tiny microbes' speed and direction are subjected to the physical vagaries of the fluid around them.

The research team led by Jay Tang, associate professor of physics at Brown University, showed how this microbe's movement is affected by drag and a phenomenon called Brownian motion.

"For bacteria to swim in water, it's like us trying to swim through honey. The drag is dominant," said Tang.

For the study, the researchers analysed the swimming patterns of one particular bacterium called, Caulobacter crescentus.

Caulobacter is a single-celled organism with a filament-like tail called a flagellum. As it swims, its rounded cellular head rotates in one direction, while the tail rotates in the opposite direction.

This creates torque, which helps explain the bacterium's nonlinear movement through a fluid.

Tang and his team also found that the movement of Caulobacter also is influenced by Brownian motion, which is the zigzagging motion that occurs when immersed particles are buffeted by the actions of the molecules of the surrounding medium.

What that means, in effect, is that Caulobacter is being pinballed by the water molecules surrounding it as it swims.

This twin effect of hydrodynamic interaction and Brownian motion governs the circular swimming patterns of Caulobacter and many other microorganisms.

Caulobacter's swimming circles grew tighter as the bacterium got closer to a surface boundary, in this case a glass slide. The tighter circle, the team found, is the result of more drag being exerted on the microbe as it swims closer to the surface

"Random forces are always more important the smaller the object is," said Tang, whose team included Guanglai Li, assistant professor of physics (research) at Brown, and Lick-Kong Tam, a recent Brown graduate who is now studying biomedical engineering at Yale University.

The researchers suggest that the study may important implications to understanding how these organisms scavenge for food and how they approach surfaces and "stick" to them.

The findings appear online in the Proceedings of the National Academy of Sciences.

ANI