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Phage 34.13 adsorbs well to Proteus mirabilis strain n but does not form plaques on it. The DNA of the phage is severely degraded in strain n. Phage which does emerge plates on P. mirabilis strain 13 but not on n. The phenotype of strain n is r+m−. Restriction by stationary phase organisms is weaker than in early log. phase cells. The acceptor ability of n str-r for a p-lac + plasmid from strain 13 is less than that of strain 13str-r. Spheroplasts of 13 plate ϕ34.13 DNA with an efficiency of 10−7. The efficiency on strain n spheroplasts is <10−11. The transduction rate of markers by ϕ34.13 into n is only reduced to about 10−1 of the rate into strain 13. Transductants are non-lysogenic for the phage, are stable and may be retransduced. Small doses of ultraviolet radiation do not increase the transduction rate. This is interpreted to mean that ϕ34.13 transduces strain n by integration of the bacterial exogenote, which like ϕ34.13 DNA and possibly strain 13 p-lac + DNA, is degraded in strain n. nh mutants of strain n were isolated on which ϕ34.13 has an e.o.p. of 5 × 10−1 and into which ϕ34.13 transduces markers at the same rate as into strain 13. Phage 34n mutants plate on strain n. A strain n-induced host specificity was discovered which must be carried by ϕ34n for it to form plaques on n. Strain n and its nh mutants are lysogenic for ϕ13vir and produce a phage tail-like bacteriocin but neither of these factors account for the restricting and modifying properties of the strains. Phages 34.13 and 34n−1.n do not affect one another in mixed infections of strain n.
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