Small molecule communication of : the ins and outs of autoinducer and nitric oxide signaling.

SUMMARY is a Gram-negative environmental bacterium, which survives in planktonic form, colonizes biofilms, and infects protozoa. Upon inhalation of -contaminated aerosols, the opportunistic pathogen replicates within and destroys alveolar macrophages, thereby causing a severe pneumonia termed Legionnaires' disease. Gram-negative bacteria employ low molecular weight organic compounds as well as the inorganic gas nitric oxide (NO) for cell-cell communication. produces, secretes, and detects the α-hydroxyketone compound autoinducer-1 (LAI-1, 3-hydroxypentadecane-4-one). LAI-1 is secreted by in outer membrane vesicles and not only promotes communication among bacteria but also triggers responses from eukaryotic cells. detects NO through three different receptors, and signaling through the volatile molecule translates into fluctuations of the intracellular second messenger cyclic-di-guanylate monophosphate. The LAI-1 and NO signaling pathways are linked the pleiotropic transcription factor LvbR. In this review, we summarize current knowledge about inter-bacterial and inter-kingdom signaling through LAI-1 and NO by species.