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How does a bacterium move? Researchers trace its path

Read time: 2 mins
Photo : Aswin Srivatsav / Research Matters

Have you ever wondered how a tiny bacterium enters your body from the surroundings and causes havoc? A simple explanation could be that it enters your body when you take in the contaminated air or water or through contact. But, how exactly does it move around once inside the body, or even in air or water? It does so in two ways; it either wiggles around with the help of flagellum—a lash-like appendage that protrudes from the body, or uses its body weight (specifically, its head) to propel itself. So what path does it trace when it moves? A study by researchers at the Indian Institute of Technology Bombay explores just that!

The flagellum of a bacterium is in the shape of a helix, like a coiled spring. So far, many studies have provided a theoretical explanation on the possible path of a how a bacterium moves or swims using the flagellum or its body weight. But, none of them has compared these theories with experimental data because it is a challenge to simultaneously visualise the motion of the head and the flagellum, along with looking at the path of movement and tracing it.

In the study, published in the Journal of Fluid Mechanics, the researchers have created a working model and have traced the path of one such bacteria with flagella—the Escherichia coli. They have visualised the motion of the bacterium in a fluid medium and have observed that the bacterium follows two types of helical paths—a larger one and a smaller one.

The first type of helical path is caused by a small asymmetry in the distribution of mass in the head of the bacteria. So when the bacteria moves its head, it traces a path with a bigger radius and increased distance between each helical turn. The second type of motion, the researchers say, is caused by the rotation of the helical flagellum, and its speed depends on the rotation set. The path followed by this type of motion is also called the wiggling trajectory. The researchers say that these two kinds of movements help the bacterium move in the various medium at various pace.

The study is the first to detail the path of a bacteria based on a working model that can visualise the two different kinds of motion. In a world that is now dominated by bacteria, any new learning on their ways of life could help us tackle them better.