1961 Volume 7 Issue 4 Pages 243-252
A routine method of DNA-mediated transformation is described. Cells of tryptophan dependent strain (No. 160 Sr) of Bacillus subtilis, harvested at an early stationary phase of growth in a glucose minimal medium containing 0.1% yeast extract, are found to be the most competent for transformation (1st culture). When transforming DNA is added to the cells suspended in a fresh medium (2nd culture), transformation occurs linearly with the time lapse after a short lag period. The process of transformation seems independent of cell growth, although the acquisition of competence by the cells is under the control of delicate physiological conditions of the cells which are terminating exponential growth. The yeast extract which is required for the cell growth in the early 2nd culture, when added in excess, lowers the efficiency of transformation. The inhibitory effect of the supplemented medium is eliminated during the growth of cells. The similar inhibition is demonstrated by the addition of nucleotides or amino acids.
Physiological control of cell growth in the 1st culture by changing incubation conditions improves the competence. The use of chemostat or the incubation at low temperatures were proved to be an efficient way for obtaining competent cells.