Role of the cell surface in bacterial mating: requirement for intact mucopeptide in donors for the expression of surface exclusion in R+ strains of Escherichia coli.

Two derivatives of the F-like R factor R1drd19 carrying mutually exclusive resistance determinants were used to study the role of the mucopeptide in the expression of conjugal functions. The use of metabolically active penicillin spheroplasts in R+ times R- matings had no effect on the ability of the cells to donate or accept a plasmid. However, in R+ times R+ matings it was found that surface exclusion was totally abolished if the donor, but not the recipient, was a spheroplast. This result implies that the traS gene, expressed by the excluding plasmid, is dependent for its action on an intact mucopeptide layer in the donor cell, and that this interaction is independent of the transfer ability of the excluding plasmid.