9724924 Jorge C. Escalante-Semerena The long-term goal of this project work is to improve our understanding of procaryotic cell physiology, and to learn more about how the metabolic web of procaryotes is integrated. For the past several years the physiology, biochemistry and genetics of vitamin Bl2 biosynthesis and the vitamin B12-dependent catabolism of ethanolamine (EA) and 1,2-propanediol (1,2-PDL) have been studied in the enteropathogenic bacterium Salmonella typhimurium. Observations made during the course of this work, uncovered features of the catabolism of these poor carbon sources that have important, global implications for cellular physiology. The studies have discovered that glutathione (GSH) and DNA polymerase I (Po1I) are required for the utilization of propionate, EA, and 1,2-PDL. This work established for the first time a link between GSH, Po1I and cell growth. The unexpected involvement of GSH and Po1I, brought into focus the serious problems generated when the cell catabolizes carbon/energy sources such as propionate, EA, or 1,2-PDL. The conclusion reached by this work was that catabolism of these carbon sources requires cellular systems to protect both proteins and nucleic acids from reactive metabolic intermediates. However, to identify damaging intermediates of a pathway, it is essential to understand its biochemistry. This project will define the propionate catabolic pathway in S. typhimurium. This work is needed due to the gap of knowledge of how this bacterium (and other enterics) catabolize propionate. Recent work suggests that S. typhimurium catabolizes propionate via a pathway found in yeast, not via the acryloyl-CoA or the vitamin B12-dependent methylmalonyl-CoA mutase pathways typically found in procaryotes. This project will begin the biochemical analysis of the functions encoded by the recently described propionate (prp) catabolism operon, and by the cobB gene which is not part of the prp operon, but whose product is required for propionate breakdown in this bacterium. This project will provide a solid foundation for future studies on the role of metabolic intermediates in the endogenous mutagenic process, and on the strategies the cell uses to protect proteins and DNA from damage, a critical issue to cell viability and evolution.
