The free-living bioluminescent marine bacterium, Vibrio harveyi, uses another signaling molecule in addition to an acylated homoserine lactone.  This molecule, termed Autoinducer-2 (or AI-2), is a furanosyl borate diester.  AI-2, which is also produced and used by a number of Gram-negative and Gram-positive bacteria, is believed to be an evolutionary link between the two major types of quorum sensing circuits.