Relative frequencies of different kinds of spontaneous and induced mutants of pneumococci and streptococci capable of growth in the presence of streptomycin.

Ravin, Arnold W. (University of Rochester, Rochester, N.Y.), and Ajit K. Mishra. Relative frequencies of different kinds of spontaneous and induced mutants of pneumococci and streptococci capable of growth in the presence of streptomycin. J. Bacteriol. 90:1161-1173. 1965.-Mutations conferring ability to grow in the presence of streptomycin arise spontaneously and can be induced in pneumococci and streptococci. They prove to be of several phenotypic and genetic types, which may be classified as follows: VLR, LR, and HR, which confer resistance, respectively, to less than 50, between 50 and 500, and 500 or more mug/ml of streptomycin. VLR and LR mutations recombine with each other, whereas HR mutations generally replace (do not recombine with) several of the VLR and LR mutations. Spontaneously, the VLR type is several times more frequent than the LR and HR types, which are equally frequent relative to each other. Nitrous acid treatment of deoxyribonucleic acid (DNA) in vitro or ultraviolet irradiation of cells tends to produce the VLR and LR type of mutation. Streptomycin-dependent mutations are rare in the pneumococci and streptococci. One such mutation, requiring 500 to 1,000 mug/ml of streptomycin for optimal growth, arose spontaneously in a group A streptococcal strain, and was transferred via a DNA-mediated transformation to a pneumococcal strain. In the latter, the mutation proved to be very closely linked to the genetic locus at which the streptomycin-resistance mutations arise.