Keith E. Weaver

Sex pheromones and plasmid transfer in Enterococcus faecalis

Plasmid-free Enterococcus faecalis excrete peptides (sex pheromones) which specifically induce a mating response in strains harboring certain conjugative plasmids. The response is characterized by the synthesis of a fuzzy surface material, visible by electron microscopy, which is believed to facilitate the aggregation of donors and recipients. Transconjugants which receive a specific plasmid shut down the production of endogenous pheromone; however, they continue to produce pheromones specific for donors harboring different classes of plasmids. In this review, we summarize what is known about the biochemistry and genetics of this phenomenon. Some emphasis is given to the hemolysin plasmid pAD1 and the regulation of its conjugal transfer.

Construction of Enterococcus faecalis pAD1 miniplasmids: Identification of a minimal pheromone response regulatory region and evaluation of a novel pheromone-dependent growth inhibition

Several pAD1 miniplasmids were constructed that consisted of all or a portion of the pAD1 EcoRI B fragment with pheromone-inducible E region lacZ transcriptional fusions. Miniplasmids containing the entire EcoRI B fragment (the E miniplasmids) were found to regulate LacZ expression normally, indicating that sufficient information is present on this fragment to regulate a pheromone response. These plasmids also encoded normal replication functions. The E miniplasmids were further reduced by deleting a KpnI fragment. These K miniplasmids were able to perform most of the functions central to a pheromone response but failed to induce the fused transcripts to levels observed in the parental plasmids. This defect was found to be due to a pheromone-dependent growth inhibition of cells containing the K miniplasmids. Evidence indicated that this inhibition was due to transcriptional readthrough beyond the lacZ gene and into the putative replication region of the plasmid. Possible mechanisms of this inhibition as well as its potential usefulness in further examining the characteristics of the pheromone response are discussed.