Autoinducer-2 (AI-2) is a furanosyl borate diester or tetrahydroxy furan (species dependent) that—as the name suggests—is an autoinducer, a member of a family of signaling molecules used in quorum sensing.

[2][3] AI-2 arises by the reaction of 4,5-dihydroxy-2,3-pentanedione, which is produced enzymatically, with boric acid[4] and is recognized by the two-component sensor kinase LuxPQ in Vibrionaceae.

Although the luxS gene, which encodes the protein responsible for AI-2 production is widespread, the latter has mainly a primary metabolic role in the recycling of S-adenosyl-L-methionine, with AI-2 being a by-product of that process.

[7] An unequivocally AI-2 related behavior was found to be restricted primarily to organisms bearing known AI-2 receptor genes.

In reporting these findings, the researchers write that their results “suggest that crosskingdom communication occurs between eukaryotic cells and bacteria via the AI-2 bacterial quorum-sensing system.”[9]