Rhodococcal steroid catabolism and responses to environmental stresses

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Since 1995, I have held a Discovery Grant supporting a research program focused mainly on microbial catabolism of terpenoids. This diverse family of chemicals, including steroids, is abundantly produced in the natural world and has important biological effects and ecological consequences. This research program has been highly productive and made well-recognized contributions to knowledge of microbial metabolism and ecology. The program has also been the springboard for numerous individually-funded and successful projects. This proposal describes fundamental research on the soil bacterium, Rhodococcus jostii RHA1, investigating steroid catabolism and responses to environmental stresses. Objectives of the research are to (a) characterize uptake systems for the steroids, cholesterol and cholic acid, (b) elucidate the pathway for cholic acid catabolism, including responsible reactions, enzymes and genes, (c) determine mechanisms for tolerance of desiccation, osmotic stress and anoxia and (d) elucidate genetic regulatory networks controlling responses to those stresses. Primary research approaches include (a) use of a microarray to monitor expression of over 8,000 RHA1 genes, (b) deletion mutagenesis to determine gene functions, (c) expression of proteins to determine their functions and (d) measurements of steroid uptake and enzymatic activities. This research will be important, as it will contribute important new understanding of key aspects of the metabolism, physiology and ecology of Actinobacteria, a group with critical roles in the recycling of organic matter in soil. The research will also facilitate applications involving Actinobacteria or their enzymes, for drug synthesis, other industrial biotransformations (green chemistry) and bioremediation of polluted environments.