Three-dimensional structures of proteins involved in quorum sensing were first published in 2001, when the crystal structures of three LuxS orthologs were determined by X-ray crystallography. In 2002, the crystal structure of the receptor LuxP of "Vibrio harveyi" with its inducer AI-2 (which is one of the few biomolecules containing boron) bound to it was also determined. Many bacterial species, including "E. coli", an enteric bacterium and model organism for Gram-negative bacteria, produce AI-2. A comparative genomic and phylogenetic analysis of 138 genomes of bacteria, archaea, and eukaryotes found that "the LuxS enzyme required for AI-2 synthesis is widespread in bacteria, while the periplasmic binding protein LuxP is present only in "Vibrio" strains," leading to the conclusion that either "other organisms may use components different from the AI-2 signal transduction system of Vibrio strains to sense the signal of AI-2 or they do not have such a quorum sensing system at all." Farnesol is used by the fungus "Candida albicans" as a quorum sensing molecule that inhibits filamentation.