FREE CALCIUM TRANSIENTS IN CHEMOTACTIC AND NON-CHEMOTACTIC STRAINS OFESCHERICHIA-COLI DETERMINED BY USING RECOMBINANT AEQUORIN

Intracellular Ca2+ has been previously implicated in the chemotactic r esponse of Escherichia coli. However, no correlative measurements of i ntracellular free Ca2+ have been made during bacterial chemotaxis, ess ential if this is to be established. In order to monitor internal free Ca2+ in E. coli during challenge with chemotactic agents, the Ca2+-ac tivated photoprotein aequorin was expressed in a chemotactic strain (A B1157) and a nonchemotactic strain [BL21(DE3)] of E. coli. Repellents were found to cause an increase (50-150 nM) in intracellular free Ca2, whereas attractants caused a small but consistent decrease in intrac ellular free Ca2+. These data are in agreement with the proposed model that an increase in intracellular free Ca2+ causes tumbling. The effe ct of increasing external Ca2+ on the regulation of intracellular free Ca2+ in both strains was monitored by using aequorin. The resting lev el of free Ca2+ in E. coli (AB1157) was found to be 100 nM, which agre es with previous data [Gangola and Rosen (1987) J. Biol. Chem. 262, 12 570-12574]. As these results also show differences in the regulation o f intracellular free Ca2+ between the two strains in the presence of h igh external Ca2+ concentrations, this may have implications for the e ffect of high-Ca2+ environments on E. coil.