A graphic diagram of QS molecular signaling network of (A) Gram-negative bacteria: the autoinducers [

] are produced and diffused freely out of the cell. When the concentration of the autoinducers reach the threshold value, a positive feedback loop will be formed that causes more autoinducers to be synthesized. The autoinducers produced will bind to their cognate receptor [

] to form an autoinducer-receptor complex [

] which will then binds to the target promoter that lead to QS gene regulation; and (B) Gram-positive bacteria: the precursor peptide autoinducers [

] are modified and transported out of the cell by ATP-binding cassette exporter complex. When the concentration of the peptide autoinducers reach the threshold value, the sensor kinase protein will be activated and phosphorylate the response regulator protein, which will then binds to the target promoter that will lead to QS gene regulation.