THE ROLE OF THE PILUS IN RECIPIENT CELL RECOGNITION DURING BACTERIAL CONJUGATION MEDIATED BY F-LIKE PLASMIDS

The effects of defined mutations in the lipopolysaccharide (LPS) and t he outer membrane protein OmpA of the recipient cell on mating-pair fo rmation in liquid media by the transfer systems of the F-like plasmids pOX38 (F), ColB2 and R100-1 were investigated. Transfer of all three plasmids was affected differently by mutations in the rfa (LPS) locus of the recipient cell, the F plasmid being most sensitive to mutations that affected rfaP gene expression which is responsible for the addit ion of pyrophosphorylethanolamine (PPEA) to heptose I of the inner cor e of the LPS. ColB2 transfer was more strongly affected by mutations i n the heptose II-heptose III region of the LPS (rfaF) whereas R100-1 w as not strongly affected by any of the rfa mutations tested. ompA but not rfa mutations further decreased the mating efficiency of an F plas mid carrying a mutation in the mating-pair stabilization protein TraN. An F derivative with a chloramphenicol acetyltransferase (CAT) casset te interrupting the traA pilin gene was constructed and pilin genes fr om F-like plasmids (F, ColB2, R100-1) were used to complement this mut ation. Unexpectedly, the results suggested that the differences in the pilin sequences were not responsible for recognizing specific groups in the LPS, OmpA or the TraT surface exclusion protein. Other corrobor ating evidence is presented suggesting the presence of an adhesin at t he F pilus tip.