Quorum sensing as an integral component of gene regulatory networks in Gram-negative bacteria

Bacterial cell-to-cell communication (quorum sensing) relies upon the inter action of a small diffusible signal molecule with a sensor or transcription al activator to couple gene expression with cell population density, In Gra m-negative bacteria, it is now clear that N-acylhomoserine lactones bind di rectly to LuxR homologues and can be synthesized via one of three unrelated bacterial protein families and by transgenic plants. New chemical classes of signal molecules have been identified! some of which exhibit crosstalk w ith N-acylhomoserine-lactone-mediated quorum sensing. As the determinant of cell population density, quorum sensing is emerging as an integral compone nt of bacterial global gene regulatory networks responsible for facilitatin g bacterial adaptation to environmental stress. N-acylhomoserine lactones a re produced during experimental animal and human infections, and a function beyond quorum sensing has been suggested by their intrinsic immunomodulato ry and pharmacological activities.