N-mating in Escherichia coli is promoted by foaming

Foaming pro9moted the conjugal transfer of IncN plasmid R269N-1 in Escherichia coli; the theoretical basis of this phenomenon is described. The hypothesis that N-mating in conventional (non-foaming) liquid media is precluded by the fragility of the N-pilus is questioned. The environmental significance of foaming is briefly considered.