The effect of environmental and chemotactic stimuli was assessed using a fusion between the Campylobacter jejuni flaA c 28 promoter and a promoterless luxCDABE cassette on pRYluxCDABE. Environmental stimuli relevant to the enteric environment were found to modulate flaA promoter activity. pH, bovine bile, deoxycholate, L-fucose and osmolarity up-regulated the flaA promoter while viscosity resulted in down-regulation. C. jejuni chemotactic effectors, including the amino acids aspartate and glutamate and the organic acids citrate, fumarate, K-ketoglutarate and succinate up-regulated the flaA promoter. Proline, which does not elicit a chemotactic response, up-regulated the flaA promoter. ß