Printed in Great Britain

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 I x I ~-~/plaque-forming unit (p.f.u.) adsorbed (higher than.chromosomal marker transduction) to 5 x Io-8/p.f.u. adsorbed. Transduced drug resistance markers of other R factors were detected only in the presence of resident$- fac-tors 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 f i f 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 trans-ductants which were conjugally infectious the transduced R factor did not appear to be associated with the genome of the phage. Incompatibility had no demon-strable effect on transduction rates. The presence of anfi- 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 possibl