Recombinant aequorin as a probe for cytosolic free Ca 2+ in Escherichia coli

We describe a novel and simple method for the measurement of bacterial cytosolic free calcium ([Ca2+]i) using recombinant acquorin reconstituted within live bacterial cells. Using this method we have measured the effects of external calcium, complement, phagocytosis and antibiotics on the [Ca2+]i of Escherichia coli. In principle this method should be applicable to any genetically transformable organism and should suffer fewer problems than fluorescent dyes for subcellular calcium measurement. © 1991.