Bacterial degradation of the steroid compound cholate

• Applicant: Professor Dr. Bodo Philipp
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms ; Microbial Ecology and Applied Microbiology
• Term: from 2008 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 88512478

Steroid compounds comprise a large and diverse group of natural compounds occurring in all eukaryotic organisms. Steroids enter the environment by the release from and the decay of animals and plants. There, they are subject to microbial degradation. Compared to other natural compounds the metabolic pathways for microbial degradation of steroid compounds are largely unknown. In the last funding period we investigated the aerobic bacterial degradation of cholate as a model substance for natural steroids using Pseudomonas sp. strain Chol1 as a model organism. Cholate belongs to the bile salts, which are surface-active steroid compounds with toxic effects for bacteria. In particular, we elucidated the pathway for the degradation of the side chain of cholate and discovered an unexpected reaction sequence involving a novel aldolytic reaction step. In addition, we isolated further cholate-degrading bacteria and discovered initial reactions that are part of a second, yet unexplored pathway for the degradation of steroid compounds. The most important goals of the proposed projects are, first, the molecular and biochemical analysis the aldolytic reaction step involved in cholate degradation of Pseudomonas sp. strain Chol1 with purified enzymes. Second, we want to identify the adaptive mechanisms that enable strain Chol1 to grow with the toxic compound cholate using molecular methods including a transcriptome analysis. Third, we want to elucidate the unknown pathway for cholate degradation with two bacterial strains, Dietzia sp. strain Chol2 and Novosphingobium sp. strain Chol11, on the genetic and biochemical level. In this part, the initial transformation of the steroid skeleton, the degradation of the side chain and the mechanism, by which the steroid skeleton is cleaved, are in the focus of the investigations. The results of this project will increase the general current knowledge on the biochemical diversity of bacterial degradation of natural compounds. Our results will also be helpful for investigating the fate of poorly degradable synthetic steroids hormones in wastewater and in agricultural settings and could, thus, have an impact on ecotoxicological research. Finally, our study will be useful for the development and improvement of biotechnological processes for the production of pharmaceutical steroids.

• DFG Programme: Research Grants