Which statement best describes quorum sensing in bacteria?

• A. Random genetic mutation rate
• B. Sense antibiotics in the environment
• C. Spore formation
• D. Cell-density–dependent gene regulation coordinating group behaviors like virulence and biofilm formation.

Answer: (D)

Quorum sensing is a cell-density–dependent gene regulation system in which bacteria communicate with each other through signaling molecules. Each cell releases these signals, and as the population grows, the signals build up. When the signal concentration crosses a threshold, neighboring cells detect it and change gene expression in a coordinated way. This enables group behaviors that are more effective when performed together, such as producing virulence factors to help infection, forming protective biofilms, or coordinating light production in some species. This concept is distinct from random mutation rates, which are spontaneous genetic changes, and from responses driven by merely sensing antibiotics or nutrient limitation, which do not depend on community signaling to regulate collective activities like virulence or biofilm formation.