FIG. 2.

Copper block frozen/freeze-substituted E. coli during (A) no-plasmid control “mating” and (B) RP4-mediated conjugation on solid substrate (filter matings). (A) Bacteria lacking a conjugative plasmid were used as controls [E. coli HB101 (null) × E. coli SCS1 (Rif^r)]. (B) Donor contained RP4-Tra1 and RP4-Tra2 [E. coli HB101(pML123, pVWDG23110Δ0.2)], and recipient was E. coli SCS1 (Rif^r). Straight, closely appressed outer membranes are typical of junctions between bacteria in RP4-mediated mating with electron-dense material between outer membranes (arrow). Bar, 25 nm.