Abstract
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.
Highlights
Sterols, such as cholesterol (I), are steroid 3β-alcohols with alkyl side chain at C17 (Figure 1).Due to their unique lipophilic properties, these lipids play vital functions in all living organisms being essential components of the cell membrane that influence membrane fluidity, cell differentiation, and proliferation
No growth growth or or very very poor poor growth growthwas wasobserved observed in inthe thecontrol control(mineral supplemented with methylated β-cyclodextrin (MCD) but without steroids) (Figure 2A)
In our previous study [24], the clusters of the genes homologous to the known steroid catabolism genes have been predicted in the genome of N. simplex VKM Ac-2033D based on the correspondence of the operons with the operons previously studied in other works
Summary
Sterols, such as cholesterol (I), are steroid 3β-alcohols with alkyl side chain at C17 (Figure 1). Due to their unique lipophilic properties, these lipids play vital functions in all living organisms being essential components of the cell membrane that influence membrane fluidity, cell differentiation, and proliferation. Bile acids along with other essential steroids (hormones, fat-soluble vitamins, etc.) are produced from cholesterol via structural modification of the steroid core and shortening of the side chain. Genes 2020, 11, x FOR PEER REVIEW Figure 1. Principal scheme scheme of of steroid steroid degradation (ADD) and Figure. 1. Principal degradation via via androsta-1,4-diene-3,17-dione androsta-1,4-diene-3,17-dione (ADD)
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