Summary: Phage 34 transduces some R factors to strain 13. These trans-ductants can transmit the R factor by conjugation. Transduction frequencies vary from 1 × 10/plaque-forming unit (p.f.u.) adsorbed (higher than chromosomal marker transduction) to 5 × 10/p.f.u. adsorbed. Transduced drug resistance markers of other R factors were detected only in the presence of resident 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 factor occurred and some transductants were unable to transmit transduced markers by cell-to-cell contact despite the presence of resident 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 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 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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