Steroid microbial degradation plays a significant ecological role for biomass decomposition and removal/detoxification of steroid pollutants. In this study, the initial steps of cholesterol degradation and lithocholate bioconversion by a strain with enhanced 3-ketosteroid dehydrogenase (3-KSD) activity, Nocardioides simplex VKM Ac-2033D, were studied. Biochemical, transcriptomic, and bioinformatic approaches were used. Among the intermediates of sterol sidechain oxidation cholest-5-en-26-oic acid and 3-oxo-cholesta-1,4-dien-26-oic acid were identified as those that have not been earlier reported for N. simplex and related species. The transcriptomic approach revealed candidate genes of cholesterol and lithocholic acid (LCA) catabolism by the strain. A separate set of genes combined in cluster and additional 3-ketosteroid Δ1-dehydrogenase and 3-ketosteroid 9α-hydroxylases that might be involved in LCA catabolism were predicted. Bioinformatic calculations based on transcriptomic data showed the existence of a previously unknown transcription factor, which regulates cholate catabolism gene orthologs. The results contribute to the knowledge on diversity of steroid catabolism regulation in actinobacteria and might be used at the engineering of microbial catalysts for ecological and industrial biotechnology.

中文翻译：

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全基因组转录组分析揭示了单纯诺卡氏菌 VKM Ac-2033D 中胆固醇和石胆酸盐的降解机制

类固醇微生物降解对类固醇污染物的生物质分解和去除/解毒具有重要的生态作用。在这项研究中，研究了具有增强的 3-酮类固醇脱氢酶 (3-KSD) 活性的菌株 Nocardioides simplex VKM Ac-2033D 的胆固醇降解和石胆酸盐生物转化的初始步骤。使用了生化、转录组学和生物信息学方法。在甾醇侧链氧化的中间体中，cholest-5-en-26-oic acid 和 3-oxo-cholesta-1,4-dien-26-oic acid 被确定为早期未报道过的那些用于 N. simplex 和相关物种。转录组学方法揭示了该菌株对胆固醇和石胆酸 (LCA) 分解代谢的候选基因。预测了一组单独的基因组合成簇，以及可能参与 LCA 分解代谢的额外 3-酮类固醇 Δ1-脱氢酶和 3-酮类固醇 9α-羟化酶。基于转录组学数据的生物信息学计算表明存在一种以前未知的转录因子，它调节胆酸盐分解代谢基因直向同源物。该结果有助于了解放线菌中类固醇分解代谢调节的多样性，并可用于生态和工业生物技术的微生物催化剂工程。