Recombinant Extracellular Cholesterol Oxidase from Nocardioides simplex

Creation and Characterization of Mycolicibacterium Smegmatis mc2155 with Deletions in Genes Encoding Sterol Oxidation Enzymes

The fast-growing saprotrophic strain Mycolicibacterium smegmatis mc2155 is capable of utilizing plant and animal sterols and can be used for creation of genetically engineered strains producing biologically active steroids. Oxidation of the 3β-hydroxyl group and Δ5(6)→Δ4(5) double bond isomerization followed by formation of stenones from sterols are considered as the initial stage of steroid catabolism in some actinobacteria. The study of the mechanism of steroid nucleus 3β-hydroxyl group oxidation is relevant for the creation of a method of the microbiological production of valuable 3β-hydroxy-5-en-steroids. A mutant strain of M. smegmatis with deletions in three genes (MSMEG_1604, MSMEG_5228 and MSMEG_5233) encoding known enzymes exhibiting 3β-hydroxysteroid dehydrogenase activity was constructed by homologous recombination coupled with double selection. The resulting mutant retained macromorphological properties and the ability to convert cholesterol. 3-Keto-4-en-steroids were found among the sterol catabolism intermediates. Experimentally obtained data indicate the presence of a previously undetected intracellular enzyme that performs the function of 3β-hydroxysteroid dehydrogenase/Δ5(6)→Δ4(5) isomerase.

Current Trends and Perspectives in Microbial Bioconversions of Steroids

The microbiological transformation of sterols is currently the technological basis for the industrial production of valuable steroid precursors, the so-called synthons, from which a wide range of steroid and indane isoprenoids are obtained by combined chemical and enzymatic routes. These compounds include value-added corticoids, neurosteroids, sex hormones, bile acids, and other terpenoid lipids required by the medicine, pharmaceutical, food, veterinary, and agricultural industries.Progress in understanding the molecular mechanisms of microbial degradation of steroids, and the development and implementation of genetic technologies, opened a new era in steroid biotechnology. Metabolic engineering of microbial producers makes it possible not only to improve the biocatalytic properties of industrial strains by enhancing their target activity and/or suppressing undesirable activities in order to avoid the formation of by-products or degradation of the steroid core, but also to redirect metabolic fluxes in cells towards accumulation of new metabolites that may be useful for practical applications. Along with whole-cell catalysis, the interest of researchers is growing in enzymatic methods that make it possible to carry out selective structural modifications of steroids, such as the introduction of double bonds, the oxidation of steroidal alcohols, or the reduction of steroid carbonyl groups. A promising area of research is strain engineering based on the heterologous expression of foreign steroidogenesis systems (bacterial, fungal, or mammalian) that ensure selective formation of demanded hydroxylated steroids.Here, current trends and progress in microbial steroid biotechnology over the past few years are briefly reviewed, with a particular focus on the application of metabolic engineering and synthetic biology techniques to improve existing and create new whole-cell microbial biocatalysts.