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Summary: Phage 34 transduces some R factors to Proteus mirabilis strain 13. These trans-ductants can transmit the R factor by conjugation. Transduction frequencies vary from 1×10−5/plaque-forming unit (p.f.u.) adsorbed (higher than chromosomal marker transduction) to 5×10−8/p.f.u. adsorbed. Transduced drug resistance markers of other R factors were detected only in the presence of resident fi − factors in recipients and recombination between the R factors concerned could account for the fact that these transductants were able to transmit hybrid R factors by conjugation. Transduction of portions of R factors, including an fi + factor occurred and some transductants were unable to transmit transduced markers by cell-to-cell contact despite the presence of resident fi − R factors. In transductants which were conjugally infectious the transduced R factor did not appear to be associated with the genome of the phage. Incompatibility had no demonstrable effect on transduction rates. The presence of an fi − resident factor reduced transduction rates when these were measurable in the absence of the resident. In two cases which involved N group resident plasmids this reduction was possibly due to restriction and host modification of transduced R factor DNA. Because of the natural resistance of the P. rettgeri host only R factors which bore the marker for kanamycin resistance could be selected in transductions with phage 7.R49. Only a T group factor was transduced. The transduction frequency was similar to that of a chromosomal marker but transductants were non-infectious.
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