Bacterial extrachromosomal elements (plasmids) represent a biologically and clinically significant pool of genetic information in a wide variety of pathogenic and non-pathogenic genera. Plasmids are known to confer such properties as multiple antibiotic resistance, toxin production, antigen production, bacteriocin production, conjugal donor ability and expanded physiological capabilities. Furthermore, the study of plasmid deoxyribonucleic acid (DNA) has greatly advanced our understanding of procaryotic cell genetics by providing us with systems of genetic and physical gene transfer and manipulation. Work completed in this project has established that the extrachromosomal gene pool of S. mutans is not as prevalent as in other gram positive bacteria. Fewer than 10% of some 60 strains of S. mutans from a variety of sources has been found to contain plasmid DNA. At least four unique plasmid DNA species have been found and preliminary data suggest that two of these plasmids occur in (at least) two independently isolated strains. Plasmid DNAs have been isolated by cesium chloride-ethidium bormide equilibrium centrifugation and have been physically compared using velocity sedimentation, agarose gel electrophoresis and electron microscopy. Plasmid-containing strains are currently under comparative physiological study with closely related but plasmid-free strains. Parameters such as antibiotic resistance, heavy metal resistance, sugar fermentation, bacteriocin production, antigen production, sensitivity to ultraviolet light, blood cell hemolysis and relative growth rates are being examined in attempting to correlate plasmid presence with phenotypic function. Any positive correlation obtained in these studies will be further tested by treating plasmid-containing strains with agents known to promote plasmid loss and examining such strains for the loss of the presumed plasmid-associated phenotype. It is hoped that the study of plasmid systems will advance our understanding of the genetics of S. mutans and will enable us to more fully explore the genetic and biochemical bases of cariogenicity and glucan synthesis in this important group of oral microbes. BIBLIOGRAPHIC REFERENCES: Markowitz, S.M., F.L. Macrina and P.V. Phibbs. 1977. Studies of the genetic basis of exopolysaccharide production in Pseudomonas aeruginosa. Abst. Ann. Meeting American Soc. Microbiol. In Press.