What characterizes a motile bacterium?

A motile bacterium is characterized by its ability to move towards or away from stimuli, a phenomenon known as taxis. This movement is often facilitated by structures such as flagella, which allow the bacterium to propel itself through its environment. The ability to move toward a favorable environment, such as nutrients, or away from harmful conditions is crucial for survival and adaptation.

This characteristic is essential for the bacterium's ability to find resources, escape predators, or avoid unfavorable conditions. Unlike the other options, which either imply non-movement or limit movement to one direction, the correct answer reflects the full range of motility that motile bacteria possess. This dual capability enhances their adaptability and efficiency in their ecological niches.