Bacterial degradation of the steroid compound cholate

甾类化合物包括存在于所有真核生物中的大量多样的天然化合物。类固醇通过动物和植物的释放和腐烂进入环境。在那里，它们会被微生物降解。与其他天然化合物相比，微生物降解类固醇化合物的代谢途径在很大程度上是未知的。在上一个资助期，我们研究了有氧细菌降解胆酸盐作为天然类固醇的模式物质，使用假单胞菌属菌株Chol1作为模式生物。胆酸盐属于胆盐，胆盐是具有表面活性的类固醇化合物，对细菌具有毒性作用。特别是，我们阐明了胆酸侧链的降解途径，并发现了一个意想不到的反应序列，涉及一个新的醇解反应步骤。此外，我们进一步分离了胆酸降解细菌，并发现了第二种尚未探索的类固醇化合物降解途径的一部分初始反应。本课题的主要目标是：首先，利用纯化酶对假单胞菌Chol1降解胆酸盐的醇解反应步骤进行分子和生化分析。其次，我们希望利用包括转录组分析在内的分子方法，确定使菌株Chol1与有毒化合物胆酸盐一起生长的适应机制。第三，我们希望利用Dietzia sp.菌株Chol2和Novosphingobium sp.菌株Chol11这两种细菌，在遗传和生化水平上阐明胆酸降解的未知途径。在这一部分中，类固醇骨架的初始转化，侧链的降解以及类固醇骨架被劈裂的机制是研究的重点。该项目的结果将增加对细菌降解天然化合物的生化多样性的一般当前知识。我们的研究结果也将有助于研究废水和农业环境中难以降解的合成类固醇激素的命运，从而可能对生态毒理学研究产生影响。最后，我们的研究将有助于开发和改进生产药用类固醇的生物技术工艺。

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.