What does quorum sensing coordinate in microbial populations at high cell densities?

• A. It triggers rapid lysis of neighboring cells.
• B. It directly increases growth rate regardless of density.
• C. It coordinates gene expression based on cell-population density.
• D. It only affects virulence factor production, not biofilm formation.

Answer: (C)

Quorum sensing is a communication system that bacteria use to sense how many neighbors are nearby by releasing and detecting signaling molecules. When cell density is high, these signals accumulate to a threshold and bind to regulatory proteins to switch genes on or off across the population. This is why the best answer describes coordinating gene expression based on cell-population density—not individual growth alone—and enabling coordinated behaviors like virulence factor production, biofilm formation, and other collective traits.

It doesn’t cause rapid lysis of neighboring cells, so that option isn’t a match. It also doesn’t simply increase growth rate regardless of density; growth is still governed by resources and conditions, while quorum sensing modulates behavior. And it isn’t limited to virulence factors only; it also influences biofilm formation and other density-dependent activities.