Cell-cell interactions in conjugating Escherichia coli: role of F pili and fate of mating aggregates.

Bacterial conjugation between Escherichia coli cells was investigated by a combination of physical and genetic techniques, using Hfr, F', or R+ donors and F- recipients. DNA transfer occurred in mating aggregates of up to 50 cells. Multiple interactions between donor and recipient cells occurred, and both F- pilus connections and wall-to-wall contacts were detectable. The detectable F- pilus contacts could be destroyed without either disrupting the mating aggregates or preventing DNA transfer. Hfr X F- mating aggregates did not disaggregate even though recombinant frequencies were inversely proportional to the distance from the origin of DNA transfer. F' or R+ donors formed mating aggregates with F- cells which disaggregated soon after transfer of the autonomous sex factor DNA.