Which of the following is a characteristic feature of motile bacteria?

Motile bacteria are primarily characterized by their ability to move, and one of the key structures that facilitate this movement is the presence of flagella. Flagella are long, whip-like appendages that rotate to propel the bacterium forward in liquid environments, allowing for directed movement towards nutrients or away from harmful substances. This motility is critical for survival, as it helps bacteria navigate their surroundings efficiently.

While other characteristics like a Gram-positive cell wall, capsule formation, and endospore production can be present in various bacteria, they do not directly contribute to the ability of bacteria to actively move. Gram-positive cell walls relate to the structural integrity and staining properties rather than motion. Capsules can enhance protection but do not aid in motility, and endospores are a dormant survival form that is not involved in active movement. Thus, the presence of flagella is the defining feature of motile bacteria, establishing their capacity for locomotion.