Quorum sensing signal in Gram-negative bacteria is usually
Quorum sensing allows bacteria to monitor local population density through the accumulation of secreted autoinducer molecules. Once a threshold concentration is reached, the autoinducer binds a cognate receptor and triggers coordinated changes in gene expression, including virulence-factor production or biofilm formation. The process therefore couples individual cell behavior to collective density.
Ref: NCERT Biology Class 11–12 Alberts et al Molecular Biology of the Cell Lodish et al, Molecular Cell Biology Cooper & Hausman, The Cell Abbas et al., Cellular and Molecular Immunology (for immunology sections)