[Competency of Escherichia coli cells. IV. Effect of freezing--thawing on the formation of competency in Escherichia coli cells in the presence of Ca++ ions].

The paper is initiated in the aim to use the effect of freezing-thawing in the system of intact Escherichia coli cells treated with Ca++ ions to increase the transfection efficiency. It is demonstrated that freezing-thawing of Ca++ treated cells increases the transfection indices of lambda phage DNA for E. coli Hfr clone with low transfection indices in 20-30 times, and for the strain of E. coli X7026 of high competence-in 5 times. Freezing-thawing efficiently increased the transfection only in cells with a decreasing competence. E. coli Hfr H cells acquired the capacity of more efficient lambda phage DNA perception independently on the growth phase, while in E. coli X7026 cells the maximal transfection increase under the effect of complementary interactions was observed at the beginning of the logariphmic and stationary growth stages, but not during the competence period. Short-term changes emerging in cells during freezing-thawing can probably promote the better penetration of Ca++ ions to active sites on the cell surface, which produces favourable conditions for lambda phage DNA formation.