On the Nature of the Recipient Ability of Salmonella typhimurium for Foreign Deoxyribonucleic Acids

SUMMARY: A fertile mutant (fer) isolated from Salmonella typhimurium LT-7mut with a mutator gene mut was found to have a high recipient ability when used as a recipient of the Escherichia coli chromosome and F’ and R factors, whereas LT-7mut + and S. typhimurium LT-2mut +, both of which lack the mut gene, were poor recipients of these foreign deoxyribonucleic acids, LT-7mut exhibited an intermediate recipient ability. These episomal elements, however, were transferred from LT-7mut and LT-7mut + to the mut, mut + and fer substrains at frequencies comparable to an E. coli recipient. In contrast, the frequencies of transfer of these episomes from LT-7fer to the other substrains of S. typhimurium were considerably lower than those to LT-7fer. The efficiencies of plating (e.o.p.) of phage P-22 grown on LT-7fer were likewise lower on LT-7mut, LT-7mur – and LT-2mut + than on LT-7fer. The e.o.p. of phage P-22 on LT-7mut, LT-7mut + and LT-7mut + were increased to the value on LT-7fer by its growth on LT-7mut + or LT-2mut +. The frequencies of transduction of an R factor to these substrains of S. typhimurium with phage P-22 grown on various substrains were parallel with the e.o.p. of this phage on these strains. It was further shown that the deoxyribonucleic acid of phage P-22, which had previously been propagated on LT-7fer, injected into LT-7mut + and LT-2mut + is rapidly degraded, whereas appreciable breakdown did not occur in LT-7fer. These results with P-22 indicate that LT-7fer is a mutant which is impaired in its capacity of restriction and modification of this phage. The growth of P-22 on LT-7mut resulted in partial increase of its e.o.p. on LT-7mut + and LT-2mut +, indicating that the restriction and modification capacities of LT-7mut are partially affected. The above results, that LT-7fer acts as a good recipient in the conjugal transfer of E. coli chromosome and non-viral episomes and that the frequencies of transfer of the non-viral episomes among the substrains of S. typhimurium are comparable to those to LT-7fer and E. coli, are interpreted as due to the restriction- and modification-less nature of LT-7fer.