Derek Englert, Chemical Engineering, Texas A&M University, Department of Chemical Engineering, 3122 TAMU, College Station, TX 77840, Michael Manson, Biology, Texas A&M University, 3258 TAMU, Biological Sciences Building East - Room 301A, College Station, TX 77843-3258, Thomas K. Wood, Artie McFerrin Department of Chemical Engineering, Texas A&M University, 200 Jack E. Brown Building, MS 3122, College Station, TX 77843-3122, Harihara Baskaran, Chemical Engineering, Case Western Reserve University, A.W.Smith Building, 10900 Euclid Avenue, Cleveland, OH 44106, and Arul Jayaraman, Department of Chemical Engineering, Texas A&M University, College Station, TX 77843-3122.
The GI tract is enervated by millions of neurons as part of the enteric nervous system (ENS) that is involved in the production of several neuroendocrine hormones, including norepinephrine, dopamine, and melatonin, in the gastrointestinal (GI) tract. The high local concentration of these molecules in the GI tract often leads to the spill over of these molecules into the intestinal lumen. Therefore, it is not surprising that enteric pathogens such as E. coli O157:H7 (EHEC) recognize and respond to these hormones as they pass through the GI tract. In addition to these hormones, pathogens also encounter molecules from the ~ 10
12 commensal (non-pathogenic) bacteria that reside in the intestines. These bacteria produce a wide spectrum of molecules, such as the quorum sensing molecules AI-2 and AI-3. Thus, enteric pathogens are exposed to both eukaryotic and prokaryotic molecules as they attempt to colonize the GI tract. Understanding the effects that these molecules exert on the pathogen is important in developing therapeutic approaches for controlling GI tract infections.
Enteric pathogens entering the GI tract are also likely to encounter gradients of different signals (rather than uniform concentrations) as the different signals are not uniformly produced throughout the GI tract. The spillover of eukaryotic hormones likely results in radial gradients at different locations. Similarly, the distribution of the non-pathogenic gut microflora also results in a spatial gradient of the different prokaryotic signals. We hypothesized that the spatial gradients of signaling molecules govern the initial colonization of the GI tract by EHEC that leads to infection. Using an agarose plug chemotaxis assay with fluorescently labeled EHEC, we demonstrated that the catecholamines epinephrine and norepinephrine attract EHEC while the E. coli derived signal indole repels the pathogen. A microfluidic chemotaxis model was developed to expose EHEC to precise spatial gradients of signaling molecules. Our data show that the EHEC response is strongly impacted by the gradient it encounters. Currently, work is in progress on using isogenic mutants for the different E. coli chemotaxis receptors to investigate the mechanism(s) through which bacteria recognize eukaryotic signals. Data on the E. coli response to various combinations and gradients of eukaryotic and prokaryotic signals, like norepinephrine and indole, will also be presented.