Why are bacterias nonmotile?

Answer 1

Not all bacteria are nonmotile. The reason some bacteria cannot move freely is because they lack one of the 3 known types of motile structures:

1.-Flagella: they are protein (flagellin) based threads, many times the bacterias own length. They are anchored in the cell wall and rotate, causing the flagella to spin in a whip-like pattern, thus propelling the bacteria.

2.-Gas vesicles: some bacteria use small gas bubbles produced inside of them to move up an down the water column, like aquatic bacteria that need to rise to the surface to receive more sunlight.

3.-Sliding: a few bacteria have been found to move only over solid surfaces using a theorized caterpillar-like mechanism akin to the tread wheels of a tank.

All bacteria that do not have one of the above mentioned movement types are termed nonmotile. Under the microscope, they seem to move in random directions by what is called Brownian movement, which is a random displacement caused by collisions with other cells, microcurrents, etc.

Answer 2

Bacteria can be nonmotile if they lack flagella or other motility structures that enable movement. Nonmotile bacteria rely on passive methods of dispersal, such as wind or water currents, or they might rely on other organisms for transportation. Additionally, some bacteria have evolved to be nonmotile as a survival strategy in certain environments.