Deciphering Bacterial Universal Language by Detecting the Quorum Sensing Signal, Autoinducer-2, with a Whole-Cell Sensing System

Abstract

Bacteria communicate with neighboring bacteria of the same species or of other species by means of chemical signaling molecules. The concentration of such signaling molecules is proportional to the bacterial population size; upon reaching a threshold concentration, corresponding to a threshold cell density, certain specialized genes are expressed. This system of communication among bacteria is known as quorum sensing (QS). QS regulates diverse behaviors, such as formation of biofilms and production of pathogenic factors. Autoinducer-2 (AI-2) is a QS signaling molecule that is used for interspecies communication by both Gram-positive and Gram-negative bacteria. Bacteria are known to play an important role in many diseases, from infections to chronic inflammation. Therefore, QS is involved in a variety of disorders of bacterial origin or where bacteria play a crucial pathogenic role. One such condition is inflammatory bowel disease (IBD), a chronic inflammation of the gastrointestinal (GI) tract that includes debilitating diseases, such as ulcerative colitis (UC) and Crohn's disease (CD). To date, noninvasive methods are unavailable for the diagnosis and monitoring of IBD. We hypothesized that detection of QS molecules in physiological samples, specifically saliva and stool specimens, would provide with a method for the noninvasive, early diagnosis and monitoring of IBD conditions. To that end, we developed and optimized a whole-cell sensing system for AI-2, which is based on Vibrio harveyi strain BB170. Furthermore, we standardized and applied the biosensing system for the quantitative detection of AI-2 in saliva, stool, and intestinal samples from IBD patients.