Factors affecting transformation of Bacillus licheniformis.

Thorne, Curtis B. (Fort Detrick, Frederick, Md.), and Harold B. Stull. Factors affecting transformation of Bacillus licheniformis. J. Bacteriol. 91:1012-1020. 1966.-Transformation systems involving two types of transformable mutants of Bacillus licheniformis 9945A were compared. Each system required its specific growth medium, but a single transformation medium could be used for both. Cells from a culture of optimal age were not competent, at least to any great extent, but they developed competence during incubation in a transformation medium. With each system, 3 to 5% of the recipient cells were transformed upon exposure to wild-type deoxyribonucleic acid (DNA) for 2 to 3 hr. When competent cells were exposed to DNA for 30 min, 1 to 2% of them were transformed. The data are interpreted to mean that cells were heterogeneous with respect to development of competence, and when properly grown cells were incubated in transformation medium some of them gained competence, whereas others lost it. If DNA was present during the entire period, the cells were transformed as they became competent and the transformants accumulated. However, during any short period of exposure to DNA, only those cells that were competent at the time were potential transformants. The high frequencies of transformation obtained in these studies made it feasible to prepare marked strains by transforming markers into recipient cells. These experiments demonstrated that the characteristics of the two transformation systems could not be attributed to specific nutritional markers. Presumably, each of the two series of highly transformable auxotrophic mutants also carried at least one other mutation that resulted in development of competence under the specific conditions.