Episome-mediated Transfer of Drug Resistance in Enterobacteriaceae X. Restriction and Modification of Phages by fi− R Factors

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Watanabe, Tsutomu (Keio University, Tokyo, Japan), Toshiya Takano, Toshihiko Arai, Hiroshi Nishida, and Sachiko Sato. Episome-mediated transfer of drug resistance in Enterobacteriaceae. X. Restriction and modification of phages by fi− R factors. J. Bacteriol. 92:477–486. 1966.—An fi− R factor, which restricts phages λ, T1, and T7 without modifying them, was found to restrict and not to modify an F−-specific phage, W-31, in Escherichia coli K-12, but not to restrict phage P-22 in Salmonella typhimurium LT-2, whereas other fi− R factors restricted and modified P-22 but not W-31; fi+ R factors did not restrict these phages. Transduction and lysogenization with phages λ and P-22 were reduced by these fi− R factors in K-12 and LT-2, respectively, and the transducing phages λ and P-22 were modified by these fi− R factors. Spontaneous as well as ultraviolet-induced production of phage P-22 and zygotic induction of phage λ were not significantly affected by any R factor. Injection of the nucleic acids of phages T1 and λ was not affected by R factors, but the injected phage nucleic acids were rapidly broken down in the bacteria carrying fi− R factors. The nucleic acids of the modified phages were not broken down in these bacteria. It was assumed from these results that the mechanism of restriction of phages by fi− R factors is due to the breakdown of the injected phage nucleic acids by a deoxyribonuclease(s), presumably located near the cell surface in the cells carrying fi− R factors. The deoxyribonuclease(s), formed in the cells carrying the nonmodifying fi− R factor, is considered to be different from that synthesized in the cells carrying the modifying fi− R factors. It was further shown that the average burst sizes of the unmodified as well as modified phages are slightly reduced by the presence of the fi− R factors.

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