Chemotaxis—movement toward or away from a chemical—is a universal behavior of motile cells and organisms. Pioneering work in the last few decades of the 1800s, notably by Engelmann, Pfeffer, and Beijerinck, first demonstrated chemotactic and aerotactic behaviors in bacteria. See reference 1 for an intriguing summary of those early studies, which were largely overlooked for the next 50 years or ...
