„tet‐gene pick up”︁ durch ein F‐Plasmid in Proteus mirabilis

Abstract

The Proteus mirabilis strains PG193 (his‐ tet+ rec+), PG273 (thr‐ tet+ rec+), and PG672 (thr‐ tet+ rec+) are full resistant to 40 μg tetracyclin/ml, similar to other 513 wild type strains tested. The F‐plasmid was introduced from Escherichia coli WF+ into these strains and into the tet‐ P. mirabilis Pm2098 by conjugation. Pure F+ P. mirabilis strains are sensitive to the F‐specific phage fr. The transfer of the F‐plasmid from F+ P. mirabilis back to E. coli K12 strains occurs with high frequency.In several cases the F‐plasmid is able to transfer the tet‐gene from tet+ rec+ P. mirabilis strains (PG193, PG273) to E. coli recipients but not from F+ P. mirabilis tet+ rec‐ (PG672) or from F+ P. mirabilis tet‐ strains (Pm2098).E. coli tet+ recombinants are sensitive to the F‐specific phage fr. They harbor F‐plasmids stably linked to the tet‐gene. Such recombinant plasmids are transferable with high frequency to other F‐R‐ members of the Enterobacteriaceae but with reduced frequency of transmission to E. coli Hfr(H) indicating a superinfection immunity.These results coincide with the Campbell modell and point to the fact that the “gene pick up” may be the (or one) way of R‐plasmid origin as proposed by Watanabe (1963).