The research proposed is focused on mammals and microorganisms indigenous to their gastrointestinal tracts. The long-term goals are to learn how such microorganisms remain and proliferate in their habitats and how they influence certain physiological activities in their animal hosts. The specific aims are to learn 1) the mechanisms by which indigenous microorganisms associate with gastrointestinal epithelial surfaces, and 2) the mechanisms by which such microorganisms modify the rates of mitosis and extrusion of intestinal epithelial cells. Germfree, gnotobiotic and specific pathogen-free rodents are used. Findings from the research help guide experiments on related research with humans, especially research concerned with how pathogenic bacteria and yeasts adhere to epithelial surfaces. The findings help as well to explain observations made in instestinal diseases in man (e.g., "small bowel overgrowth" syndrome, pseudomembranous colitis and neonatal botulism), and add to a body of knowledge on prokaryote-eukaryotic interactions of interest to cell biologists and ecologists. In research toward the first specific aims, strains of indigenous bacteria (especially anaerobic species) and yeast are isolated from epithelial surfaces in the murine gastrointestinal tract. Surface components of the microbial cells are isolated, purified and assayed for their function in the adhesion of the cells to the epithelial surface. Genes encoding such materials are localized (on plasmids or chromosomes), cloned by recombinant DNA techniques, and utilized in attempts to confirm the molecular identity of microbial adhesives. In research toward the second specific aim, epithelial cells (enterocytes) are isolated from the upper small intestines of germfree mice and mice associated with a microflora. Extracts of the cells are assayed for enzymes that catalyze reactions important in the uptake of nucleic acid precursors and their incorporation into cellular DNA and RNA. The rates of mitosis and extrusion of the epithelial cells are also compared in the germfree and associated mice.