Detection of external chemical signals is important for whole organisms, in the senses of taste and smell, as well as being important for individual cells. Calcium ions have been implicated in responses of cells to external signals, including chemical signals. Bacteria have been developed as a model system for conveniently studying the ways in which chemical signals affect the cellular machinery of responsiveness. Bacteria in a liquid medium swim with a flagella; when it rotates clockwise they "run", but when it rotates counterclockwise the show extensive tumbling and reorientation. While swimming, they show behavior called chemotaxis; swimming toward sources of chemical attractant compounds is a positive response, and tumbling away from repellents is a negative response. This project investigates the role of calcium ions in these opposite responses, and the mechanisms involved in the calcium ion actions. A simple assay of bacteria swimming into capillary tubes provides behavioral data, fluorescence calcium- sensitive dyes measure calcium ion concentrations, and labeled phosphate compounds that are taken up by proteins allow measuring the effect of calcium ions on metabolic reactions related to chemotaxis. This work will have important impact on chemosensory science and bacterial biology, but also will have an impact on understanding cellular mechanisms of behavior in other organisms because calcium ions play key roles in the action of nerves and muscles.
