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