text: * P. aeruginosa also uses 2-heptyl-3-hydroxy-4-quinolone (PQS) for quorum sensing.  This molecule is noteworthy because it does not belong to the homoserine lactone class of autoinducers.  PQS is believed to provide an additional regulatory link between the Las and Rhl circuits involved in virulence and infection.
  * Agrobacterium tumefaciens is a plant pathogen that induces tumors on susceptible hosts.  Infection by A. tumefaciens involves the transfer of an oncogenic plasmid from the bacterium to the host cell nucleus, while quorum sensing controls the conjugal transfer of plasmids between bacteria.  Conjugation, on the other hand, requires the HSL autoinducer, N-(3-oxooctanoyl)-homoserine lactone.
  * Erwinia carotovora is another plant pathogen that causes soft-rot disease.  These bacteria secrete cellulases and pectinases, which are enzymes that degrade plant cell walls.  ExpI/ExpR are LuxI/LuxR homologs in E. carotovora believed to control secretion of these enzymes only when a high enough local cell density is achieved.  The autoinducer involved in quorum sensing in E. carotovora is N-(3-oxohexanoyl)-L-homoserine lactone.