Genetic Recombination of Transforming Deoxyribonucleic Acid Molecules with the Recipient Genome and Among Themselves in Protoplasts of Bacillus subtilis

Hirokawa, Hideo (Southwest Center for Advanced Studies, Dallas, Tex.), and Yonosuke Ikeda. Genetic recombination of transforming deoxyribonucleic acid molecules with the recipient genome and among themselves in protoplasts of Bacillus subtilis. J. Bacteriol. 92:455-463. 1966.-Re-extraction of transforming deoxyribonucleic acid (DNA) from protoplasts of Bacillus subtilis is much more efficient than from intact competent cells. This facilitated the detection of physical recombination between donor and recipient DNA molecules, as indicated by a high cotransfer index of ind(+) and his(+) markers which were originally located in exogenous and endogenous DNA molecules, respectively. This recombinant DNA was extracted after 30 min of incubation of ind his(+) protoplasts with ind(+)his DNA, previously extracted from a corresponding mutant strain of B. subtilis. The intracellular formation of recombinant molecules (ind(+)his(+)) bearing markers from two different exogenous DNA species was also detected 15 min after exposure of ind his recipient protoplasts to a mixture of ind(+)his and ind his(+) donor DNA molecules. The unity of the recombinant molecule was ascertained by dilution experiments and by its being resistant to ribonuclease and trypsin treatment (but being sensitive to deoxyribonuclease). The formation of recombinant molecules showed an inverse kinetics to that of the intracellularly induced loss of linkage between the corresponding markers in the wild-type DNA, thus suggesting a breakage and reunion process which is also favored by the absence of DNA synthesis in the protoplasts and the effect of some specific inhibitors.