Gary M. Dunny

Plasmid transfer in Streptococcus faecalis: Production of multiple sex pheromones by recipients

In a previous report (1978, Proc. Nat. Acad. Sci. USA 75, 3479-3483), we showed that recipient strains of Streptococcusfaecalis excrete a heat-stable substance (sex pheromone) which induces donor cells carrying certain conjugative plasmids to become adherent, generating the cell-to-cell contact necessary for plasmid transfer. Since donors themselves could be induced to aggregate or “clump” by recipient filtrates, the substance was referred to as “clumping-inducing agent” (CIA). In this report, we present a simplified assay for CIA and determine the level of activity in filtrates prepared at various stages of growth. We also present evidence that recipient cells produce multiple pheromones, each specific for donors harboring a particular class of plasmids. Whereas a recipient that acquires a conjugative plasmid no longer produces the corresponding CIA, it still produces CIAs specific for donors with different conjugative plasmids. In addition, an analysis of 100 clinical isolates of S. faecalis showed that drug-resistant strains are significantly more likely to respond to and produce CIA activities than drug-sensitive strains. A model is discussed describing the relationships of sex pheromones to the mating process.

Buoyant densities of DNA from various strains of Streptococcus mutans

CARIOGENESIS has been correlated with the presence of certain streptococci in the oral cavity and on tooth surfaces. Various studies dealing with the serological relationships of cariogenic strains resembling Streptococcus mutans (CLARKE, 1924; EDWARDSSON, 1968) have implied a certain amount of heterogeneity within this group (Tow and SHKLAIR, 1967; ZINNER and JABLON, 1968; BRATTHALL, 1970). Recent studies by COYKENDALL (1970; 1971), involving melting point determinations and homology studies on deoxyribonucleic acid extracted from different strains, indicate that these microorganisms vary widely in their genetic material and should probably be classified into several groups. In this communication, we present data dealing with CsCl buoyant density determinations on DNA isolated from various strains of Strept. mutans and essentially con