Figure 2.

The LuxR/AHL-mediated quorum sensing regulation of multiple gene expressions in Gram-negative bacteria. The 'R' and 'I' genes are homologues of the LuxR and LuxI genes in which the 'R' protein is the AHL receptor and signal transducer while I protein is AHL signal synthase. The I protein is responsible for the production of AHLs. After synthesis, AHLs get diffuse (short chain) or pumped out (long chain) of the bacterial cell into the surrounding medium prior to being taken up into nearby bacterial cells. The AHL activate R protein by direct binding to make AHL/R protein complex which rapidly increases I gene expression and hence AHL production. At a certain level of bacterial cells, the quorum sensing system becomes fully activated which leads to R-mediated expression of quorum sensing target genes.