The tendency to tumble is enhanced when the bacterium perceives conditions to be worsening — when attractant concentrations decrease or repellent concentrations increase. Conversely, tumbling is suppressed and cells keep running when they detect that conditions are improving.

Why do bacteria tumble?

“Food” for bacteria is usually a simple sugar, such as glucose. … Because of the way that the flagella are shaped, they don’t propel the bacterium when rotating in the opposite direction, but rather cause the bacterium to “tumble” so that when it starts swimming again, it is moving in a random direction.

How do bacteria move in chemotaxis?

Chemotaxis is the directed motion of an organism toward environmental conditions it deems attractive and/or away from surroundings it finds repellent. Movement of flagellated bacteria such as Escherichia coli can be characterized as a sequence of smooth-swimming runs punctuated by intermittent tumbles.