Optimal Conditions for the Transformation of Streptococci.

Perry, Dennis (Northwestern University Medical School, Chicago, Ill.) and Hutton D. Slade. Optimal conditions for the transformation of streptococci. J. Bacteriol. 85:636-642. 1963.-A study of the properties of the streptococcal transforming system, employing streptomycin resistance as a marker, resulted in a 1,000- to 10,000-fold increase in the rate of transformation. In some cases, as high as 0.5% transformants have been obtained. Certain aspects of the system differed markedly from those of other bacterial transforming systems, particularly with regard to the time for the appearance of competence. When a group H strain was exposed to deoxyribonucleic acid after various periods of incubation, the time at which cells were most competent was about 2 hr. Similar experiments with a different group H strain and an ungroupable strain showed that competence for both occurred after 1 hr of growth. It is significant that the period of optimal competence, though attained at different times, took place at the beginning of the logarithmic phase of growth. The temperature optimum for transformation was about 37 C. Cells preincubated in sheepblood broth exhibited a higher level of transformation than cells preincubated in plain or human serum broth. That some correlation exists between the attainment of competence and growth is evident. In contrast, human serum was most effective in the transforming media. The few preparations of bovine albumin (fraction V) employed did not appreciably support transformation. Data are also presented which show that some relationship exists between transforming efficiency and serological classification, in that homologous transformation showed a 100- to 10,000-fold greater efficiency over heterologous transformation. Antibodies to deoxyribonuclease, as well as other inhibitors of deoxyribonuclease, failed to bring about transformation in group A streptococci.