N-Hexadecanoyl-L-homoserine lactone is a small diffusible signaling molecule and is a member of N-acyl-homoserine lactone family. N-acylhomoserine lactones (AHL) are involved in quorum sensing, controlling gene expression, and cellular metabolism. C16-HSL is a lipophilic, long acyl side-chain bearing AHL, produced by the LuxI AHL synthase homolog SinI involved in quorum-sensing signaling in S. meliloti, a nitrogen-fixing bacterial symbiont of certain legumes. C16-HSL is the most abundant AHL produced by the proteobacterium R. capsulatus and activates genetic exchange between R. capsulatus cells. It tends to localize in relatively lipophilic cellular environments of bacteria and cannot diffuse freely through the cell membrane. The long-chain N-acylhomoserine lactones may be exported from cells by efflux pumps or may be transported between communicating cells by extracellular outer membrane vesicles.