LuxS converts S-ribosylhomocysteine to homocysteine and 4,5-dihydroxy-2,3-pentanedione (DPD); DPD can then spontaneously cyclise to active AI-2. [ 1 ] [ 2 ] AI-2 is a signalling molecule that functions in interspecies communication by regulating niche-specific genes with diverse functions in various bacteria , often in response to population density . LuxS