SUMMARY: Capsular transformation of strain rd was examined at the cellular level by a semi-quantitative method. Type b capsular antigen synthesized by transformants was detected by its reaction with type b antibody conjugated to fluorescein isothiocyanate. Deoxyribonucleate (DNA) preparations from type b capsular transformants of strain rd elicited somewhat higher frequencies of transformation than preparations from type b clinical isolates. markers on these DNAs conferred resistance to a concentration of 500 μg. dihydrostreptomycin sulphate/ml. For a given DNA, the frequency of transformation to streptomycin resistance was at least 100 times higher than that to capsular synthesis. The time course of expression of the two phenotypes by DNA-treated bacteria was examined in broth in which the generation time of the total population was about 50 min. Resistant transformants began to appear 25 min. after initiation of treatment and capsulated bacteria were observed after 40 min. Both properties continued to be expressed until about 120 min. Thereafter, the behaviour of recipients of the two kinds of genetic markers differed. The rate of increase of the transformants became equal to that of the total population, and in a subculture diluted 1/20 they increased 20-fold during subsequent incubation for 150 min. The number of capsulated transformants, on the other hand, increased less than two-fold over the period 120-330 min.


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