[Quantity of compentent cells in a population of Escherichia coli treated with Ca2+ cations]

An attempt was made to estimate the number of Escherichia coli K-12 cells rendered permeable to antibiotics under Ca2+ treatment. The effect of cold factor and Ca2+ alone as well as the cell age on the induction of permeability and the energy dependence of the latter were also investigated. About 70-75% and more exponentially growing cells as a result of Ca2+ treatment became sensitive to actinomycin, rubomycin and olivomycin. This number was somewhat lower (40-50%) in sationary phase culture. A fraction (20-30%) of stationary phase cells appeared to be sensitive to antibiotics even without Ca2+ pretreatment. Preincubation of the cells in cold in the absence of Ca2+ cations did not induce the cell permeability. The transport of antibiotics inside the cell was not prevented by an uncoupler of oxidative phosphorylation --carbonylcyanid-m-chlorophenylhydrazone (CCCP). It is suggested that the cells which are rendered permeable to tested antibiotics represent the "compentent" cells capable to uptake molecules of exogenous DNA as well.