New Insights on Steroid Biotechnology

Holistic transcriptional responses of Cordyceps militaris to different culture temperatures

Cordyceps militaris is a medicinal entomopathogenic fungus containing valuable biometabolites for pharmaceutical applications. Its genetic inheritance and environmental factors play a crucial role in the production of biomass enriched with cordycepin. While temperature is a crucial controlled parameter for fungal cultivation, its impacts on growth and metabolite biosynthesis remains poorly characterized. This study aimed to investigate the metabolic responses and cordycepin production of C. militaris strain TBRC6039 under various temperature conditions through transcriptome analysis. Among 9599 expressed genes, 576 genes were significantly differentially expressed at culture temperatures of 15 and 25 °C. The changes in the transcriptional responses induced by these temperatures were found in several metabolisms involved in nutrient assimilation and energy source, including amino acids metabolism (e.g., glycine, serine and threonine metabolism) and lipid metabolism (e.g., biosynthesis of unsaturated fatty acids and steroid biosynthesis). At the lower temperature (15 °C), the biosynthetic pathways of lipids, specifically ergosterol and squalene, were the target for maintaining membrane function by transcriptional upregulation. Our study revealed the responsive mechanisms of C. militaris in acclimatization to temperature conditions that provide an insight on physiological manipulation for the production of metabolites by C. militaris.

Shy is a Proteobacterial steroid hydratase which catalyzes steroid side chain degradation without requiring a catalytically inert partner domain

Shy (side chain hydratase) and Sal (side chain aldolase), are involved in successive reactions in the pathway of bile acid side chain catabolism in Proteobacteria. Untagged Shy co-purified with His-tagged Sal indicating that the two enzymes form a complex. Shy contains a MaoC and a DUF35 domain. When co-expressed with Sal, the DUF35 domain but not the MaoC domain of Shy was observed to co-purify with Sal, indicating Sal interacts with Shy through its DUF35 domain. The MaoC domain of Shy (ShyMaoC) remained catalytically viable and could hydrate cholyl-enoyl-CoA with similar catalytic efficiency as in the Shy-Sal complex. Sal expressed with the DUF35 domain of Shy (Sal-ShyDUF35) was similarly competent for the retroaldol cleavage of cholyl-3-OH-CoA. ShyMaoC showed a preference for C5 side chain bile acid substrates, exhibiting low activity towards C3 side chain substrates. The ShyMaoC structure was determined by X-ray crystallography, showing a hot dog fold with a short central helix surrounded by a twisted anti-parallel β-sheet. Modeling and mutagenesis studies suggest that the bile acid substrate occupies the large open cleft formed by the truncated central helix and repositioning of the active site housing. ShyMaoC therefore contains two substrate binding sites per homodimer, making it distinct from previously characterized MaoC steroid hydratases that are (pseudo)-heterodimers with one substrate binding site per dimer. The characterization of Shy provides insight into how MaoC family hydratases have adapted to accommodate large polycyclic substrates that can facilitate future engineering of these enzymes to produce novel steroid pharmaceuticals.

Design, synthesis and molecular modeling of novel D-ring substituted steroidal 4,5-dihydropyrazole thiazolinone derivatives as anti-inflammatory agents by inhibition of COX-2/iNOS production and down-regulation of NF-κB/MAPKs in LPS-induced RAW264.7 macrophage cells

It has been reported that 4,5-dihydropyrazole and thiazole derivatives have many biological functions, especially in the aspect of anti-inflammation. According to the strategy of pharmacophore combination, we introduced thiazolinone and dihydropyrazole moiety into steroid skeleton to design and synthesize a novel series of D-ring substituted steroidal 4,5-dihydropyrazole thiazolinone derivatives, and assessed their in vitro anti-inflammatory profiles against Lipopolysaccharide (LPS)-induced inflammation in RAW 264.7 macrophage cells. The anti-inflammatory activities assay demonstrated that compound 12e was considered as the most effective anti-inflammatory drug, which suppressed the expression of pro-inflammatory mediators including nitric oxide (NO), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α), it also dose-dependently inhibited the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in LPS-induced RAW 264.7 macrophage cells. Furthermore, the results of the Western blot analysis showed a correlation between the inhibition of the Nuclear factor-kappa B (NF-κB) and Mitogen-activated protein kinases (MAPKs) signaling pathways and the suppressive effects of compound 12e on pro-inflammatory cytokines. Molecular docking studies of compound 12e into the COX-2 protein receptor (PDB ID: 5IKQ) active site was performed to rationalize their COX-2 inhibitory potency. The results were found to be in line with the biological findings as they exerted more favorable interactions compared to that of dexamethasone (DXM), explaining their remarkable COX-2 inhibitory activity. The findings revealed that these candidates could be identified as potent anti-inflammatory agents, compound 12e could be a promising drug for the treatment of inflammatory diseases.

Cytochrome P450 Mining for Bufadienolide Diversification

Bufadienolides are a class of steroids with a distinctive α-pyrone ring at C17, mostly produced by toads and consisting of over 100 orthologues. They exhibit potent cardiotonic and antitumor activities and are active ingredients of the traditional Chinese medicine Chansu and Cinobufacini. Direct extraction from toads is costly, and chemical synthesis is difficult, limiting the accessibility of active bufadienolides with diverse modifications and trace content. In this work, based on the transcriptome and genome analyses, using a yeast-based screening platform, we obtained eight cytochrome P450 (CYP) enzymes from toads, which catalyze the hydroxylation of bufalin and resibufogenin at different sites. Moreover, a reported fungal CYP enzyme Sth10 was found functioning in the modification of bufalin and resibufogenin at multiple sites. A total of 15 bufadienolides were produced and structurally identified, of which six were first discovered. All of the compounds were effective in inhibiting the proliferation of tumor cells, especially 19-hydroxy-bufalin (2) and 1β-hydroxy-bufalin (3), which were generated from bufalin hydroxylation catalyzed by CYP46A35. The catalytic efficiency of CYP46A35 was improved about six times and its substrate diversity was expanded to progesterone and testosterone, the common precursors for steroid drugs, achieving their efficient and site-specific hydroxylation. These findings elucidate the key modification process in the synthesis of bufadienolides by toads and provide an effective way for the synthesis of unavailable bufadienolides with site-specific modification and active potentials.

Efficient Production of 9,22-Dihydroxy-23,24-bisnorchol-4-ene-3-one from Phytosterols by Modifying Multiple Genes in Mycobacterium fortuitum

C19 steroids and C22 steroids are vital intermediates for the synthesis of steroid drugs. Compared with C19 steroids, C22 steroids are more suitable for synthesizing progesterone and adrenocortical hormones, albeit less developed. 9,22-dihydroxy-23,24-bisnorchol-4-ene-3-one(9-OHBA), due to its substituents at positions C-9 and C-22, is a beneficial and innovative steroid derivative for synthesizing corticosteroids. We focused on the C22 pathway in Mycobacterium fortuitum ATCC 35855, aiming to develop a productive strain that produces 9-OHBA. We used a mutant strain, MFΔkstD, that knocked out kstds from Mycobacterium fortuitum ATCC 35855 named MFKD in this study as the original strain. Hsd4A and FadA5 are key enzymes in controlling the C19 metabolic pathway of steroids in Mycobacterium fortuitum ATCC 35855. After knocking out hsd4A, MFKDΔhsd4A accumulated 81.47% 9-OHBA compared with 4.13% 9-OHBA in the strain MFKD. The double mutant MFKDΔhsd4AΔfadA5 further improved the selectivity of 9-OHBA to 95.13%, and 9α-hydroxy-4-androstenedione (9-OHAD) decreased to 0.90% from 4.19%. In the end, we obtained 6.81 g/L 9-OHBA from 10 g/L phytosterols with a molar yield of 80.33%, which showed the best performance compared with formerly reported strains.

Combining Metabolic Engineering and Lipid Droplet Assembly to Achieve Campesterol Overproduction in Saccharomyces cerevisiae

Campesterol is a kind of important functional food additive. Therefore, stable and efficient campesterol biosynthesis is significant. Herein, we first knocked out the sterol 22-desaturase gene in Saccharomyces cerevisiae and expressed sterol Δ7-reductase from Pangasianodon hypophthalmus, obtaining a strain that produced 6.6 mg/L campesterol. Then, the modular expression of campesterol synthesis enzymes was performed, and a campesterol titer of 88.3 mg/L was achieved. Because campesterol is a lipid-soluble macromolecule, we promoted lipid droplet formation by exploring regulatory factors, and campesterol production was improved to 169.20 mg/L. Next, triacylglycerol lipase was used to achieve compartment campesterol synthesis. After enhancing the expression of sterol Δ7-reductase and screening cations, the campesterol titer reached 438.28 mg/L in a shake flask and 1.44 g/L in a 5 L bioreactor, which represents the highest campesterol titer reported to date. Metabolic regulation combined with lipid droplet engineering may be useful for the synthesis of other steroids as well.

Bioassay-guided isolation of anti-leukemic steroids from Aglaia abbreviata by inducing apoptosis

The strategy of bioactivity-guided isolation is widely used to obtain active compounds as quickly as possible. Thus, the inhibitory effects on human erythroleukemia cells (HEL) were applied to guide the isolation of the anti-leukemic compounds from Aglaia abbreviata. As a result, 19 compounds (16 steroids, two phenol derivatives, and a rare C12 chain nor-sesquiterpenoid), including 13 new compounds, were isolated and identified based on spectroscopic data analysis, single-crystal X-ray diffraction data, and electronic circular dichroism (ECD) calculations. Among them, 9 steroids exhibited good selective anti-leukemic activity against HEL and K562 (human chronic myeloid leukemia cells) cells with IC50 values between 2.29 ± 0.18 μM and 19.58 ± 0.13 μM. Notably, all the active compounds had relatively lower toxicity on the normal human liver cell line (HL-7702). Furthermore, five compounds (1, 4, 8, 10, and 19) displayed good anti-inflammatory effects, with IC50 values between 7.15 ± 0.16 and 27.1 ± 0.37 μM. An α,β-unsaturated ketone or a 5,6Δ double bond was crucial for improving anti-leukemic effect from the structure-activity relationship analysis. The compound with the most potential, 14 was selected for the preliminary mechanistic study. Compound 14 can induce apoptosis and cause cell cycle arrest. The expression of the marker proteins, such as PARP and caspase 3, were notably effected by this compound, thus inducing apoptosis. In conclusion, our investigation implied that compound 14 may serve as a potential anti-leukemia agent.

Immobilization of rough morphotype Mycolicibacterium neoaurum R for androstadienedione production

OBJECTIVES

Enhance the androstadienedione (Androst-1,4-diene-3,17-dione, ADD) production of rough morphotype Mycolicibacterium neoaurum R by repeated-batch fermentation of immobilized cells.

RESULTS

M. neoaurum R was a rough colony morphotype variant, obtained from the routine plating of smooth M. neoaurum strain CICC 21097. M. neoaurum R showed rougher cell surface and aggregated in broth. The ADD production of M. neoaurum R was notably lower than that of M. neoaurum CICC 21097 during the free cell fermentation, but the yield gap could be erased after proper cell immobilization. Subsequently, repeated-batch fermentation of immobilized M. neoaurum R was performed to shorten the production cycle and enhance the bio-production efficiency of ADD. Through the optimization of the immobilization carriers and the co-solvents for phytosterols, the ADD productivity of M. neoaurum R immobilized by semi-expanded perlite reached 0.075 g/L/h during the repeated-batch fermentation for 40 days.

CONCLUSIONS

The ADD production of the rough-type M. neoaurum R was notably enhanced by the immobilization onto semi-expanded perlite. Moreover, the ADD batch yields of M. neoaurum R immobilized by semi-expanded perlite were maintained at high levels during the repeated-batch fermentation.

Microbial metabolism of diosgenin by a novel isolated Mycolicibacterium sp. HK-90: A promising biosynthetic platform to produce 19-carbon and 21-carbon steroids

Green manufacture of steroid precursors from diosgenin by microbial replacing multistep chemical synthesis has been elusive. It is currently limited by the lack of strain and degradation mechanisms. Here, we demonstrated the feasibility of this process using a novel strain Mycolicibacterium sp. HK-90 with efficiency in diosgenin degradation. Diosgenin degradation by strain HK-90 involves the selective removal of 5,6-spiroketal structure, followed by the oxygenolytic cleavage of steroid nuclei. Bioinformatic analyses revealed the presence of two complete steroid catabolic gene clusters, SCG-1 and SCG-2, in the genome of strain HK-90. SCG-1 cluster was found to be involved in classic phytosterols or cholesterol catabolic pathway through the deletion of key kstD1 gene, which promoted the mutant m-∆kstD1 converting phytosterols to intermediate 9α-hydroxyandrostenedione (9-OHAD). Most impressively, global transcriptomics and characterization of key genes suggested SCG-2 as a potential gene cluster encoding diosgenin degradation. The gene inactivation of kstD2 in SCG-2 resulted in the conversion of diosgenin to 9-OHAD and 9,16-dihydroxy-pregn-4-ene-3,20-dione (9,16-(OH)2 -PG) in mutant m-ΔkstD2. Moreover, the engineered strain mHust-ΔkstD1,2,3 with a triple deletion of kstDs was constructed, which can stably accumulate 9-OHAD by metabolizing phytosterols, and accumulate 9-OHAD and 9,16-(OH)2 -PG from diosgenin. Diosgenin catabolism in strain mHust-ΔkstD1,2,3 was revealed as a progression through diosgenone, 9,16-(OH)2 -PG, and 9-OHAD to 9α-hydroxytestosterone (9-OHTS). So far, this work is the first report on genetically engineered strain metabolizing diosgenin to produce 21-carbon and 19-carbon steroids. This study presents a promising biosynthetic platform for the green production of steroid precursors, and provide insights into the complex biochemical mechanism of diosgenin catabolism.

Actinobacteria as Microbial Cell Factories and Biocatalysts in The Synthesis of Chiral Intermediates and Bioactive Molecules; Insights and Applications

Actinobacteria are one of the most intriguing bacterial phyla in terms of chemical diversity and bioactivities of their reported biomolecules and natural products, including various types of chiral molecules. Actinobacterial genera such as Detzia, Mycobacterium, and Streptomyces are among the microbial sources targeted for selective reactions such as asymmetric biocatalysis catalyzed by whole cells or enzymes induced in their cell niche. Remarkably, stereoselective reactions catalyzed by actinobacterial whole cells or their enzymes include stereoselective oxidation, stereoselective reduction, kinetic resolution, asymmetric hydrolysis, and selective transamination, among others. Species of actinobacteria function with high chemo-, regio-, and enantio-selectivity under benign conditions, which could help current industrial processing. Numerous selective enzymes were either isolated from actinobacteria or expressed from actinobacteria in other microbes and hence exploited in the production of pure organic compounds difficult to obtain chemically. In addition, different species of actinobacteria, especially Streptomyces species, function as natural producers of chiral molecules of therapeutic importance. Herein, we discuss some of the most outstanding contributions of actinobacteria to asymmetric biocatalysis, which are important in the organic and/or pharmaceutical industries. In addition, we highlight the role of actinobacteria as microbial cell factories for chiral natural products with insights into their various biological potentialities.

Efficiency aspects of regioselective testosterone hydroxylation with highly active CYP450-based whole-cell biocatalysts

Steroid hydroxylations belong to the industrially most relevant reactions catalysed by cytochrome P450 monooxygenases (CYP450s) due to the pharmacological relevance of hydroxylated derivatives. The implementation of respective bioprocesses at an industrial scale still suffers from several limitations commonly found in CYP450 catalysis, that is low turnover rates, enzyme instability, inhibition and toxicity related to the substrate(s) and/or product(s). Recently, we achieved a new level of steroid hydroxylation rates by introducing highly active testosterone-hydroxylating CYP450 BM3 variants together with the hydrophobic outer membrane protein AlkL into Escherichia coli-based whole-cell biocatalysts. However, the activity tended to decrease, which possibly impedes overall productivities and final product titres. In this study, a considerable instability was confirmed and subject to a systematic investigation regarding possible causes. In-depth evaluation of whole-cell biocatalyst kinetics and stability revealed a limitation in substrate availability due to poor testosterone solubility as well as inhibition by the main product 15β-hydroxytestosterone. Instability of CYP450 BM3 variants was disclosed as another critical factor, which is of general significance for CYP450-based biocatalysis. Presented results reveal biocatalyst, reaction and process engineering strategies auguring well for industrial implementation of the developed steroid hydroxylation platform.

Identification of the aldolase responsible for the production of 22-hydroxy-23,24-bisnorchol-4-ene-3-one from natural sterols in Mycolicibacterium smegmatis

Mycobacterial mutants blocked in ring degradation constructed to achieve C19 synthons production, also accumulate by-products such as C22 intermediates throughout an alternative pathway reducing the production yields and complicating the downstream purification processing of final products. In this work, we have identified the MSMEG_6561 gene, encoding an aldolase responsible for the transformation of 22-hydroxy-3-oxo-cholest-4-ene-24-carboxyl-CoA (22-OH-BCN-CoA) into the 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) precursor (20S)-3-oxopregn-4-ene-20-carboxaldehyde (3-OPA). The deletion of this gene increases the production yield of the C-19 steroidal synthon 4-androstene-3,17-dione (AD) from natural sterols, avoiding the production of 4-HBC as by-product and the drawbacks in the AD purification. The molar yield of AD production using the MS6039-5941-6561 triple mutant strain was checked in flasks and bioreactor improving very significantly compared with the previously described MS6039-5941 strain.

Phytosterol conversion into C9 non-hydroxylated derivatives through gene regulation in Mycobacterium fortuitum

Androst-4-ene-3,17-dione (AD) and 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC) are important drug intermediates that can be biosynthesized from phytosterols. However, the C9 hydroxylation of steroids via 3-ketosteroid 9α-hydroxylase (KSH) limits AD and 4-HBC accumulation. Five active KshAs, the oxidation component of KSH, were identified in Mycobacterium fortuitum ATCC 35855 for the first time. The deletion of kshAs indicated that the five KshA genes were jointly responsible for C9 hydroxylation during phytosterol biotransformation. MFKDΔkshA, the five KshAs deficient strain, blocked C9 hydroxylation and produced 5.37 g/L AD and 0.55 g/L 4-HBC. The dual function reductase Opccr knockout and 17β-hydroxysteroid dehydrogenase Hsd4A enhancement reduced 4-HBC content from 8.75 to 1.72% and increased AD content from 84.13 to 91.34%, with 8.24 g/L AD being accumulated from 15 g/L phytosterol. In contrast, hsd4A and thioesterase fadA5 knockout resulted in the accumulation of 5.36 g/L 4-HBC from 10 g/L phytosterol. We constructed efficient AD (MFKDΔkshAΔopccr_hsd4A) and 4-HBC (MFKDΔkshAΔhsd4AΔfadA5) producers and provided insights for further metabolic engineering of the M. fortuitum ATCC 35855 strain for steroid productions. KEY POINTS: • Five active KshAs were first identified in M. fortuitum ATCC 35855. • Deactivation of all five KshAs blocks the steroid C9 hydroxylation reaction. • AD or 4-HBC production was improved by Hsd4A, FadA5, and Opccr modification.

Synthesis of Metabolites and Metabolite-like Compounds Using Biocatalytic Systems

Methodologies for the synthesis and purification of metabolites, which have been developed following their discovery, analysis, and structural identification, have been involved in numerous life science milestones. The renewed focus on the small molecule domain of biological cells has also created an increasing awareness of the rising gap between the metabolites identified and the metabolites which have been prepared as pure compounds. The design and engineering of resource-efficient and straightforward synthetic methodologies for the production of the diverse and numerous metabolites and metabolite-like compounds have attracted much interest. The variety of metabolic pathways in biological cells provides a wonderful blueprint for designing simplified and resource-efficient synthetic routes to desired metabolites. Therefore, biocatalytic systems have become key enabling tools for the synthesis of an increasing number of metabolites, which can then be utilized as standards, enzyme substrates, inhibitors, or other products, or for the discovery of novel biological functions.

Advances and Challenges in Plant Sterol Research: Fundamentals, Analysis, Applications and Production

Plant sterols (PS) are cholesterol-like terpenoids widely spread in the kingdom Plantae. Being the target of extensive research for more than a century, PS have topped with evidence of having beneficial effects in healthy subjects and applications in food, cosmetic and pharmaceutical industries. However, many gaps in several fields of PS's research still hinder their widespread practical applications. In fact, many of the mechanisms associated with PS supplementation and their health benefits are still not fully elucidated. Furthermore, compared to cholesterol data, many complex PS chemical structures still need to be fully characterized, especially in oxidized PS. On the other hand, PS molecules have also been the focus of structural modifications for applications in diverse areas, including not only the above-mentioned but also in e.g., drug delivery systems or alternative matrixes for functional foods and fats. All the identified drawbacks are also superimposed by the need of new PS sources and technologies for their isolation and purification, taking into account increased environmental and sustainability concerns. Accordingly, current and future trends in PS research warrant discussion.

Research progress in steroidal saponins from the genus Polygonatum: Chemical components, biosynthetic pathways and pharmacological effects

The genus Polygonatum Mill. belongs to the Liliaceae family, which is widely distributed all over the world. Modern studies have found that Polygonatum plants are very rich in chemical compounds such as saponins, polysaccharides and flavonoids. Steroidal saponins are the most commonly studied saponins in the genus Polygonatum and a total of 156 compounds have been isolated from 10 species of the genus. These molecules possess antitumor, immunoregulatory, anti-inflammatory, antibacterial, antiviral, hypoglycemic, lipid-lowering and anti-osteoporotic activities. In this review, we summarize recent advances in studies of the chemical constituents of steroidal saponins from Polygonatum, including their structural characteristics, possible biosynthetic pathways and pharmacological effects. Then, the relationship between the structure and some physiological activities is considered. This review aims to provide reference for further exploitation and utilization of the genus Polygonatum.

Expression of Synthetic cyp102A1-LG23 Gene and Functional Analysis of Recombinant Cytochrome P450 BM3-LG23 in the Actinobacterium Mycolicibacterium smegmatis

Cytochrome CYP102A1 (P450 BM3) of Priestia megaterium (bas. Bacillus megaterium) has several unique functional features and thus provides an ideal object for directed evolution and other synthetic applications. Previously, the CYP102A1-LG23 mutant with 14 mutations in the heme part was obtained that hydroxylates several androstanes at C7β with the formation of products with the anti-inflammatory and neuroprotective activities. In this study, synthetic cyp102A1-LG23 gene encoding the P450 BM3 mutant was expressed as a component of either monocistronic operon or bicistronic operon containing the gdh (glucose dehydrogenase, GDH) or zwf2 (glucose 6-phosphate dehydrogenase, G6PD) gene in Mycolicibacterium smegmatis BD cells. The recombinant bacteria were able hydroxylate androst-4-ene-3,17-dione (AD) into 7β-OH-AD. Their biocatalytic activity was increased twice by increasing the solubility of CYP102A1-LG23 protein in the cells and supplementing the cells with the additional cofactor regeneration system by introducing GDH and G6PD. The maximum 7β-OH-AD yield (37.68 mol%) was achieved by co-expression of cyp102A1-LG23 and gdh genes in M. smegmatis. These results demonstrate the possibility of using synthetic genes to obtain recombinant enzymes and expand our understanding of the processes involved in steroid hydroxylation by bacterial cytochromes. The data obtained can be used to develop new approaches for microbiological production of 7β-hydroxylated steroids in genetically modified Mycolicibacterium species.

Driving the conversion of phytosterol to 9α-hydroxy-4-androstene-3,17-dione in Mycolicibacterium neoaurum by engineering the supply and regeneration of flavin adenine dinucleotide

BACKGROUND

The conversion of phytosterols to steroid synthons by engineered Mycolicibacteria comprises one of the core steps in the commercial production of steroid hormones. This is a complex oxidative catabolic process, and taking the production of androstenones as example, it requires about 10 equivalent flavin adenine dinucleotide (FAD). As the high demand for FAD, the insufficient supply of FAD may be a common issue limiting the conversion process.

RESULTS

We substantiated, using the production of 9α-hydroxy-4-androstene-3,17-dione (9-OHAD) as a model, that increasing intracellular FAD supply could effectively increase the conversion of phytosterols into 9-OHAD. Overexpressing ribB and ribC, two key genes involving in FAD synthesis, could significantly enhance the amount of intracellular FAD by 167.4% and the production of 9-OHAD by 25.6%. Subsequently, styrene monooxygenase NfStyA2B from Nocardia farcinica was employed to promote the cyclic regeneration of FAD by coupling the oxidation of nicotinamide adenine dinucleotide (NADH) to NAD⁺, and the production of 9-OHAD was further enhanced by 9.4%. However, the viable cell numbers decreased by 20.1%, which was attributed to sharply increased levels of H₂O₂ because of the regeneration of FAD from FADH₂. Thus, we tried to resolve the conflict between FAD regeneration and cell growth by the overexpression of catalase and promotor replacement. Finally, a robust strain NF-P2 was obtained, which could produce 9.02 g/L 9-OHAD after adding 15 g/L phytosterols with productivity of 0.075 g/(L h), which was 66.7% higher than that produced by the original strain.

CONCLUSIONS

This study highlighted that the cofactor engineering, including the supply and recycling of FAD and NAD⁺ in Mycolicibacterium, should be adopted as a parallel strategy with pathway engineering to improve the productivity of the industrial strains in the conversion of phytosterols into steroid synthons.

Whole-Genome Analysis of Mycobacterium neoaurum DSM 1381 and the Validation of Two Key Enzymes Affecting C22 Steroid Intermediates in Sterol Metabolism

Mycobacterium neoaurum DSM 1381 originated from Mycobacterium neoaurum ATCC 25790 by mutagenesis screening is a strain of degrading phytosterols and accumulating important C22 steroid intermediates, including 22-hydroxy-23, 24-bisnorchola-4-en-3-one (4-HP) and 22-hydroxy-23, 24-bisnorchola-1,4-dien-3-one (HPD). However, the metabolic mechanism of these C22 products in M. neoaurum DSM 1381 remains unknown. Therefore, the whole-genome sequencing and comparative genomics analysis of M. neoaurum DSM 1381 and its parent strain M. neoaurum ATCC 25790 were performed to figure out the mechanism. As a result, 28 nonsynonymous single nucleotide variants (SNVs), 17 coding region Indels, and eight non-coding region Indels were found between the genomes of the two strains. When the wild-type 3-ketosteroid-9α-hydroxylase subunit A1 (KshA1) and β-hydroxyacyl-CoA dehydrogenase (Hsd4A) were overexpressed in M. neoaurum DSM 1381, the steroids were transformed into the 4-androstene-3, 17- dione (AD) and 1,4-androstadiene-3,17-dione (ADD) instead of C22 intermediates. This result indicated that 173N of KshA1 and 171K of Hsd4A are indispensable to maintaining their activity, respectively. Amino acid sequence alignment analysis show that both N173D in KshA1 and K171E in Hsd4A are conservative sites. The 3D models of these two enzymes were predicted by SWISS-MODEL and AlphaFold2 to understand the inactivation of the two key enzymes. These results indicate that K171E in Hsd4A may destroy the inaction between the NAD+ with the NH3+ and N173D in KshA1 and may disrupt the binding of the catalytic domain to the substrate. A C22 steroid intermediates-accumulating mechanism in M. neoaurum DSM 1381 is proposed, in which the K171E in Hsd4A leads to the enzyme's inactivation, which intercepts the C19 sub-pathways and accelerates the C22 sub-pathways, and the N173D in KshA1 leads to the enzyme's inactivation, which blocks the degradation of C22 intermediates. In conclusion, this study explained the reasons for the accumulation of C22 intermediates in M. neoaurum DSM 1381 by exploring the inactivation mechanism of the two key enzymes.

Improving the production of 9α-hydroxy-4-androstene-3,17-dione from phytosterols by 3-ketosteroid-Δ1-dehydrogenase deletions and multiple genetic modifications in Mycobacterium fortuitum

BACKGROUND

9α-hydroxyandrost-4-ene-3,17-dione (9-OHAD) is a significant intermediate for the synthesis of glucocorticoid drugs. However, in the process of phytosterol biotransformation to manufacture 9-OHAD, product degradation, and by-products restrict 9-OHAD output. In this study, to construct a stable and high-yield 9-OHAD producer, we investigated a combined strategy of blocking Δ¹‑dehydrogenation and regulating metabolic flux.

RESULTS

Five 3-Ketosteroid-Δ¹-dehydrogenases (KstD) were identified in Mycobacterium fortuitum ATCC 35855. KstD2 showed the highest catalytic activity on 3-ketosteroids, followed by KstD3, KstD1, KstD4, and KstD5, respectively. In particular, KstD2 had a much higher catalytic activity for C9 hydroxylated steroids than for C9 non-hydroxylated steroids, whereas KstD3 showed the opposite characteristics. The deletion of kstDs indicated that KstD2 and KstD3 were the main causes of 9-OHAD degradation. Compared with the wild type M. fortuitum ATCC 35855, MFΔkstD, the five kstDs deficient strain, realized stable accumulation of 9-OHAD, and its yield increased by 42.57%. The knockout of opccr or the overexpression of hsd4A alone could not reduce the metabolic flux of the C22 pathway, while the overexpression of hsd4A based on the knockout of opccr in MFΔkstD could remarkably reduce the contents of 9,21 ‑dihydroxy‑20‑methyl‑pregna‑4‑en‑3‑one (9-OHHP) by-products. The inactivation of FadE28-29 leads to a large accumulation of incomplete side-chain degradation products. Therefore, hsd4A and fadE28-29 were co-expressed in MFΔkstDΔopccr successfully eliminating the two by-products. Compared with MFΔkstD, the purity of 9-OHAD improved from 80.24 to 90.14%. Ultimately, 9‑OHAD production reached 12.21 g/L (83.74% molar yield) and the productivity of 9-OHAD was 0.0927 g/L/h from 20 g/L phytosterol.

CONCLUSIONS

KstD2 and KstD3 are the main dehydrogenases that lead to 9-OHAD degradation. Hsd4A and Opccr are key enzymes regulating the metabolic flux of the C19- and C22-pathways. Overexpression of fadE28-29 can reduce the accumulation of incomplete degradation products of the side chains. According to the above findings, the MF-FA5020 transformant was successfully constructed to rapidly and stably accumulate 9-OHAD from phytosterols. These results contribute to the understanding of the diversity and complexity of steroid catabolism regulation in actinobacteria and provide a theoretical basis for further optimizing industrial microbial catalysts.

New Insights into the Modification of the Non-Core Metabolic Pathway of Steroids in Mycolicibacterium and the Application of Fermentation Biotechnology in C-19 Steroid Production

Androsta-4-ene-3,17-dione (AD), androsta-1,4-diene-3,17-dione (ADD), and 9α-hydroxy-4-androstene-3,17-dione (9-OHAD), which belong to C-19 steroids, are critical steroid-based drug intermediates. The biotransformation of phytosterols into C-19 steroids by Mycolicibacterium cell factories is the core step in the synthesis of steroid-based drugs. The production performance of engineered mycolicibacterial strains has been effectively enhanced by sterol core metabolic modification. In recent years, research on the non-core metabolic pathway of steroids (NCMS) in mycolicibacterial strains has made significant progress. This review discusses the molecular mechanisms and metabolic modifications of NCMS for accelerating sterol uptake, regulating coenzyme I balance, promoting propionyl-CoA metabolism, reducing reactive oxygen species, and regulating energy metabolism. In addition, the recent applications of biotechnology in steroid intermediate production are summarized and compared, and the future development trend of NCMS research is discussed. This review provides powerful theoretical support for metabolic regulation in the biotransformation of phytosterols.

Alcohols as Efficient Intermolecular Initiators for a Highly Stereoselective Polyene Cyclisation Cascade

The use of benzylic and allylic alcohols in HFIP solvent together with Ti(Oi Pr)4 has been shown to trigger a highly stereoselective polyene cyclisation cascade. Three new carbon-carbon bonds are made during the process and complete stereocontrol of up to five new stereogenic centers is observed. The reaction is efficient, has high functional group tolerance and is atom-economic generating water as a stoichiometric by-product. A new polyene substrate-class is employed, and subsequent mechanistic studies indicate a stereoconvergent mechanism. The products of this reaction can be used to synthesize steroid-analogues in a single step.

Production of 21-hydroxy-20-methyl-pregna-1,4-dien-3-one by modifying multiple genes in Mycolicibacterium

C22 steroid drug intermediates are suitable for corticosteroids synthesis, and the production of C22 steroids is unsatisfactory due to the intricate steroid metabolism. Among the C22 steroids, 21-hydroxy-20-methyl-pregna-1,4-dien-3-one (1,4-HP) could be used for Δ¹-steroid drug synthesis, such as prednisolone. Nevertheless, the production of 1,4-HP remains unsatisfactory. In this study, an ideal 1,4-HP producing strain was constructed. By the knockout of 3-ketosteroid-9-hydroxylase (KshA) genes and 17β-hydroxysteroid dehydrogenase (Hsd4A) gene, the steroid nucleus degradation and the accumulation of C19 steroids in Mycolicibacterium neoaurum were blocked. The mutant strain could transform phytosterols into 1,4-HP as the main product and 21-hydroxy-20-methyl-pregna-4-ene-3-one as a by-product. Subsequently, the purity of 1,4-HP improved to 95.2% by the enhancement of 3-ketosteroid-Δ¹-dehydrogenase (KSTD) activity, and the production of 1,4-HP was improved by overexpressing NADH oxidase (NOX) and catalase (KATE) genes. Consequently, the yield of 1,4-HP achieved 10.5 g/L. The molar yield and the purity of 1,4-HP were optimal so far, and the production of 1,4-HP provides a new intermediate for the pharmaceutical steroid industry. KEY POINTS: • A third 3-ketosteroid-9-hydroxylase was identified in Mycolicibacterium neoaurum. • An 1,4-HP producer was constructed by KshA and Hsd4A deficiency. • The production of 1,4-HP was improved by KSTD, NOX, and KATE overexpression.

Bioconversion of 4-hydroxyestradiol by extradiol ring-cleavage dioxygenases from Novosphingobium sp. PP1Y

Livestock breeding activities and pharmaceutical wastes lead to considerable accumulation of steroid hormones and estrogens in wastewaters. Here estrogens act as pro-cancerogenic agents and endocrine disruptors interfering with the sexual development of aquatic animals and having toxic effects in humans. Environmental bacteria play a vital role in estrogens degradation. Their wide reservoir of enzymes, such as ring cleavage dioxygenases (RCDs), can degrade the steroid nucleus, catalyzing the meta-cleavage of A, B or D steroid rings. In this work, 4 extra-diol ring cleavage dioxygenases (ERCDs), PP28735, PP26077, PP00124 and PP00193, were isolated from the marine sphingomonad Novosphingobium sp. PP1Y and characterized. Enzymes kinetic parameters were determined on different synthetic catecholic substrates. Then, the bioconversion of catechol estrogens was evaluated. PP00124 showed to be an efficient catalyst for the degradation of 4-hydroxyestradiol (4-OHE2), a carcinogenic hydroxylated derivate of E2. 4-OHE2 complete cleavage was obtained using PP00124 both in soluble form and in whole recombinant E. coli cells. LC-MS/MS analyses confirmed the generation of a semialdehyde product, through A-ring meta cleavage. To the best of our knowledge, PP00124 is the first characterized enzyme able to directly degrade 4-OHE2 via meta cleavage. Moreover, the complete 4-OHE2 biodegradation using recombinant whole cells highlighted advantages for bioremediation purposes.

Loop pathways are responsible for tuning the accumulation of C19- and C22-sterol intermediates in the mycobacterial phytosterol degradation pathway

4-Androstene-3,17-dione (4-AD) and 22-hydroxy-23,24-bisnorchol-4-ene-3-one (BA) are the most important and representative C19- and C22-steroidal materials. The optimalization of sterol production with mycobacterial phytosterol conversion has been investigated for decades. One of the major challenges is that current industrial mycobacterial strains accumulate unignorable impurities analogous to desired sterol intermediates, significantly hampering product extractions and refinements. Previously, we identified Mycobacterium neoaurum HGMS2 as an efficient 4-AD-producing strain (Wang et al. in Microb Cell Fact. 19:187, 2020). Recently, we have genetically modified the HGMS2 strain to remove its major impurities including ADD and 9OH-AD (Li et al. in Microb Cell Fact. 20:158, 2021). Unexpectedly, the modified mutants started to significantly accumulate BA compared with the HGMS2 strain. In this work, while we attempted to block BA occurrence during 4-AD accumulation in HGMS2 mutants, we identified a few loop pathways that regulated metabolic flux switching between 4-AD and BA accumulations and found that both the 4-AD and BA pathways shared a 9,10-secosteroidial route. One of the key enzymes in the loop pathways was Hsd4A1, which played an important role in determining 4-AD accumulation. The inactivation of the hsd4A1 gene significantly blocked the 4-AD metabolic pathway so that the phytosterol degradation pathway flowed to the BA metabolic pathway, suggesting that the BA metabolic pathway is a complementary pathway to the 4-AD pathway. Thus, knocking out the hsd4A1 gene essentially made the HGMS2 mutant (HGMS2^Δhsd4A1) start to efficiently accumulate BA. After further knocking out the endogenous kstd and ksh genes, an HGMS2^Δhsd4A1 mutant, HGMS2^{Δhsd4A1/Δkstd1}, enhanced the phytosterol conversion rate to BA in 1.2-fold compared with the HGMS2^Δhsd4A1 mutant in pilot-scale fermentation. The final BA yield increased to 38.3 g/L starting with 80 g/L of phytosterols. Furthermore, we knocked in exogenous active kstd or ksh genes to HGMS2^{Δhsd4A1/Δ kstd1} to construct DBA- and 9OH-BA-producing strains. The resultant DBA- and 9OH-BA-producing strains, HGMS2^{Δhsd4A1/kstd2} and HGMS2^{Δkstd1/Δhsd4A1/kshA1B1}, efficiently converted phytosterols to DBA- and 9OH-BA with the rates of 42.5% and 40.3%, respectively, and their final yields reached 34.2 and 37.3 g/L, respectively, starting with 80 g/L phytosterols. Overall, our study not only provides efficient strains for the industrial production of BA, DBA and 9OH-BA but also provides insights into the metabolic engineering of the HGMS2 strain to produce other important steroidal compounds.

Biocatalysis of Steroids by Mycobacterium sp. in Aqueous and Organic Media

Mycobacterium sp. can convert steroids such as β-sitosterol, campesterol, and cholesterol, by selective side-chain cleavage and oxidation of the C3 hydroxyl group to a ketone, into key intermediates that can be easily functionalized to yield commercially interesting pharmaceutical products. In aqueous systems, the biocatalysis is limited by the low solubility of the steroids in water. Several strategies have been introduced to tackle this limitation, e.g., formation of cyclodextrin-steroid complexes and generation of aqueous microdispersions with steroid particle size in the range of hundreds of nanometers. Still, the introduction of an organic phase acting as a substrate and/or product reservoir is a well-established and relatively easy to implement strategy to overcome the sparing water solubility of steroid molecules. However, the organic phase has to be carefully chosen to prevent tampering with the activity/viability of microbial cells.In this chapter, we describe the methodology for the biocatalysis of β-sitosterol to 4-androstene-3,17-dione (AD) and 1,4-androstadiene-3,17-dione (ADD), both in aqueous and organic:aqueous systems. In the latter case, both traditional organic solvents and green solvents are proposed.

Targeted Mutagenesis of Mycobacterium Strains by Homologous Recombination

Targeted mutagenesis by homologous recombination (TMHR) is an efficient allelic exchange mutagenesis for bacterial genome engineering in synthetic biology. Unlike other allelic exchange methods, TMHR does not require a heterologous recombinase to insert or excise a selectable marker from the genome. In contrast, positive and negative selection is achieved solely by suicide vector-encoded functional and host cell proteins. Here we describe a concise protocol to knock out and knock in a 3-ketosteroid-1,2-dehydrogenase gene (kstd) in Mycobacterium neoaurum HGMS2 using TMHR approach. The homology arms flanking the kstd gene are amplified by PCR in vitro and then subcloned into a common homologous recombination vector. The vector is then electroporated into the HGMS2 competent cells. The replacement of the kstd gene by homologous recombination produces antibiotic-resistant single-crossover recombination via the first allelic exchange. Double-crossover markerless mutants are directly separated using sucrose-mediated counterselection. These two steps can generate seamless mutations down to a single DNA base pair. The whole process takes less than 2 weeks.

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.

Bidimensional Analyses of the Intra- and Extracellular Proteomes of Steroid Producer Mycobacteria

The importance of the pathogenic mycobacteria has mainly focused the omic analyses on different aspects of their clinical significance. However, those industrially relevant mycobacteria have received less attention, even though the steroid market sales in 2021 were estimated in $56.45 billion.The extracellular proteome, due to its relevance in the sterol processing and uptake, and the intracellular proteome, because of its role in steroids bioconversion, are the core of the present chapter. Both, monodimensional gels, as preparatory analysis, and bidimensional gels as proteome analysis are described. As a proof of concept, the protein extraction methods for both sub-proteomes of Mycobacterium are described. Thus, procedures and relevant key points of these proteome analyses are fully detailed.

Isolation of Environmental Bacteria Able to Degrade Sterols and/or Bile Acids: Determination of Cholesterol Oxidase and Several Hydroxysteroid Dehydrogenase Activities in Rhodococcus, Gordonia, and Pseudomonas putida

Interest about the isolation and characterization of steroid-catabolizing bacteria has increased over time due to the massive release of these recalcitrant compounds and their deleterious effects or their biotransformation derivatives as endocrine disruptors for wildlife, as well as their potential use in biotechnological approaches for the synthesis of pharmacological compounds. Thus, in this chapter, an isolation protocol to select environmental bacteria able to degrade sterols, bile acids, and androgens is shown. Moreover, procedures for the determination of cholesterol oxidase or different hydroxysteroid dehydrogenase activities in Pseudomonas putida DOC21, Rhodococcus sp. HE24.12, Gordonia sp. HE24.4J and Gordonia sp. HE24.3 are also detailed.

Obtaining of 24-Norchol-4-ene-3,22-dione from Phytosterol with Mutants of Mycolicibacterium neoaurum

Engineered mutants of Mycolicibacterium spp. are known producers of valuable steroid synthons with C19 or C22 skeleton. Here we describe a method for site-directed mutagenesis of Mycolicibacterium neoaurum strains, bioconversion from phytosterol, and selective purification of C23 steroid 24-norchol-4-ene-3,22-dione (24-NCED) and C22 steroid 20-hydroxymethylpregn-4-ene-3-one (20-HMP). The yields of crystalline products with 95% purity by the method here described are 2.74 ± 0.085 g for 24-NCED and 1.42 ± 0.085 g for 20-HMP from 10 g/L phytosterol. 20-HMP is recognized as the key precursor in chemical syntheses of pharmaceutical corticosteroids and 24-NCED is a promising synthon for the synthesis of valuable steroids and own potent biological activity.

Production of 11α-Hydroxysteroid Derivatives by Corynebacterium glutamicum Expressing the Rhizopus oryzae Hydroxylating System

Hydroxylation of steroids has acquired special relevance for the pharmaceutical industry. Particularly, the 11α-hydroxylation of steroids is a process of biotechnological importance currently carried out at industrial scale for the production of contraceptive drugs and glucocorticoids. This process is performed by several fungal species including Rhizopus nigricans, Aspergillus ochraceus, Aspergillus niger, and Rhizopus oryzae that are used to produce by biotransformation hydroxylated steroids for pharmaceutical purposes (Wang et al., J Steroid Biochem Mol Biol 171:254-261, 2017). However, the development of more efficient biotransformation processes is essential since the steroidal derivatives obtained by the in vivo hydroxylation are often a mixture of hydroxylated compounds in different positions of the steroid molecule. This phenomenon is due to the large number of different CYPs contained in the fungal strains.The genes responsible for the 11α-hydroxylase activity in R. oryzae consisting in the cytochrome CYP509C12 and its redox partner, the reductase RoCPR1, have been chemically synthetized forming a synthetic operon named FUN optimized to be expressed in bacteria. To express this operon, we have selected the strain Corynebacterium glutamicum R31 that is a robust and GRAS bacterial strain widely used for industrial purposes. The synthetic operon has been cloned in the pECXK-99E vector, yielding pXKFUN plasmid, and transformed C. glutamicum R31 to generate C. glutamicum R31 (pXKFUN) strain. This strain is not a steroid degrader and can efficiently transport C19 and C21 steroids across the cytoplasmic membrane (García-Fernandez et al. Catalysts 316:1-12, 2017). C. glutamicum can be used as a clean host for steroid biotransformation, because it does not introduce additional undesired side reactions on the steroids, thus reducing the contamination of the final products (Felpeto-Santero et al., Microbiol Biotechnol 12:856-868, 2019). Here we show a proof of concept that C. glutamicum can be used as a suitable chassis to perform steroid biotransformation expressing eukaryotic cytochromes. The protocol below provides detailed information on steroid 11α-hydroxylations by Corynebacterium recombinant strain.

Scale-Up of Phytosterols Bioconversion into Androstenedione

Phytosterols, coming as a by-product of vegetable oils or wood pulp, contain the cyclopentanoperhydrophenanthrene nucleus and can be bioconverted into steroid intermediates by removing the C17 side chain. This chapter shows the scale-up, from flask to bioreactor, of phytosterols bioconversion into 4-androstene-3,17-dione (androstenedione; AD) using Mycolicibacterium neoaurum B-3805. Due to the fact that phytosterols and AD are nearly insoluble in water, two-phase systems and the use of chemically modified cyclodextrins have been described as methods to solve it. Here, we use a water-oil two-phase system that allows the bioconversion of up to 20 g/L of phytosterols into AD in 5 L and 20 L bioreactors.

Correlation Relationship between Phase Inversion of Pickering Emulsions and Biocatalytic Activity of Microbial Transformation of Phytosterols

Microbial transformation of hydrophobic phytosterols into the pharmaceutical steroid precursors AD (androst-4-ene-3, 17-dione) and ADD (androst-4-diene-3, 17-dione) in a water–plant oil two-phase system by Mycolicibacterium neoaurum is a paradigm of interfacial biocatalysis in Pickering emulsions stabilized by bacterial cells. In the present work, phase inversion of Pickering emulsions—i.e., Pickering emulsions turning from water-in-oil (W/O) emulsions into oil-in-water (O/W) ones—was observed during microbial transformation in the presence of high concentrations of crystal phytosterols. It was found that there is a correlation relationship between the phase behaviors of Pickering emulsions and the biocatalytic activity of utilizing M. neoaurum as a whole-cell catalyst. Efficient microbial transformation under the high crystal phytosterol loadings was achieved due to the formation of O/W emulsions where interfacial biocatalysis took place. Under the optimal conditions (volume ratio of soybean oil to water: 15:35 mL, phytosterols concentration in the soybean oil: 80 g/L, glucose as co-substrate in the aqueous culture medium: 10 g/L), the concentrations of AD and ADD reached 4.8 g/L based on the whole broth (16 g/L based on the oil phase) after microbial transformation for 9 days.

Biological activity of new bioactive steroids deriving from biotransformation of cortisone

Cortisone is a metabolite belonging to the corticosteroid class that is used pharmaceutically directly as a drug or prodrug. In addition to its large consumption, its use is linked to several side effects, so pharmaceutical research aims to develop effective drugs with low or no side effects, alternative compounds to cortisone are part of an active investment in ongoing research on drug discovery. Since biotransformation can be considered a source of new molecules with potential therapeutic use, the present work focuses on a preliminary in vitro study aimed at evaluating the mutagenic, anti-inflammatory, antioxidant and neuroprotective activity of SCA and SCB molecules obtained from the biotransformation of cortisone using Rh. Rhodnii strain DSM 43960. The results obtained are very encouraging due to the safety of biotransformed compounds with reference to genotoxicity checked by Ames test, to the very high antioxidant capacity and to the anti-inflammatory activity. In fact, thecompounds inhibited both the TNFα-stimulated expression and secretion of NFkB target cytokines, and COX activity, and can activate the glucocorticoid receptor. Finally SCA and SCB exhibited neuroprotective properties.

Concise synthesis of E/F ring spiroethers from tigogenin. Carbaanalogs of steroidal sapogenins and their biological activity

A four-step synthesis of five- and six-membered E/F ring spiroethers from tigogenin has been developed. An efficient strategy that features bis-Grignard reaction of dinorcholanic lactone with appropriate bis(bromomagnesio)alkanes followed by acid-mediated spirocyclization was employed to construct a new class of steroid compounds having E and F ring junction as an oxa-carbacyclic system. The synthesized carbaanalogs interact with liposomes and albumin, and also exhibit antibacterial and antifungal activity, demonstrating their pharmacological potential.

Comparative transcriptome analysis reveals key genes for polyphyllin difference in five Paris species

Paris species accumulate a large amount of steroidal saponins, which have numerous pharmacological activities and have become an essential component in many patented drugs. However, only two among all Paris species. Paris are identified as official sources due to high level of bioactive compounds. To clarify the composition of steroidal saponins and the molecular basis behind the differences between species, we investigated transcriptome and metabolic profiles of leaves and rhizomes in Paris polyphylla var. chinensis (PPC), Paris polyphylla var. yunnanensis (PPY), Paris polyphylla var. stenophylla (PPS), Paris fargesii (PF), and Paris mairei (PM). Phytochemical results displayed that the accumulation of steroidal saponins was tissue- and species-specific. PF and PPS contained more steroidal saponins in leaves than rhizomes, while PPY accumulated more steroidal saponins in rhizomes than leaves. PPC and PM contained similar amounts of steroidal saponins in leaves and rhizomes. Transcriptome analysis illustrated that most differentially expressed genes related to the biosynthesis of steroidal saponins were abundantly expressed in rhizomes than leaves. Meanwhile, more biosynthetic genes had significant correlations with steroidal saponins in rhizomes than in leaves. The result of CCA indicated that ACAT, DXS, DWF1, and CYP90 constrained 97.35% of the variance in bioactive compounds in leaves, whereas CYP72, UGT73, ACAT, and GPPS constrained 98.61% of the variance in phytochemicals in rhizomes. This study provided critical information for enhancing the production of steroidal saponins by biotechnological approaches and methodologies.

Bioconversion of Phytosterols to 9-Hydroxy-3-Oxo-4,17-Pregadiene-20-Carboxylic Acid Methyl Ester by Enoyl-CoA Deficiency and Modifying Multiple Genes in Mycolicibacterium neoaurum

C22 steroids are valuable precursors for steroid drug synthesis, but the development of C22 steroids remains unsatisfactory. This study presented a strategy for the one-step bioconversion of phytosterols to a C22 steroid drug precursor, 9-hydroxy-3-oxo-4,17-pregadiene-20-carboxylic acid methyl ester (9-OH-PDCE), by 3-ketosteroid-Δ 1 -dehydrogenase and enoyl-CoA hydratase deficiency with overexpression of 17β-hydroxysteroid dehydrogenase acyl-CoA dehydrogenase in Mycolicibacterium .

Combined enhancement of the propionyl-CoA metabolic pathway for efficient androstenedione production in Mycolicibacterium neoaurum

Background

The production of androstenedione (AD) from phytosterols by Mycolicibacterium neoaurum is a multi-step biotransformation process, which requires degradation of sterol side chains, accompanied by the production of propionyl-CoA. However, the transient production of large amounts of propionyl-CoA can accumulate intracellularly to produce toxic effects and severely inhibit AD production.

Results

In the present study, the intracellular propionyl-CoA concentration was effectively reduced and the productivity of the strain was improved by enhancing the cytosolic methyl-branched lipid synthesis pathway and increasing the expression level of nat operator gene, respectively. Subsequently, the application of a pathway combination strategy, combined and the inducible regulation strategy, further improved AD productivity with a maximum AD conversion rate of 96.88%, an increase of 13.93% over the original strain.

Conclusions

Overall, we provide a new strategy for reducing propionyl-CoA stress during biotransformation for the production of AD and other steroidal drugs using phytosterols.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01942-x.

Rhodococcus strains as a good biotool for neutralizing pharmaceutical pollutants and obtaining therapeutically valuable products: Through the past into the future

Active pharmaceutical ingredients present a substantial risk when they reach the environment and drinking water sources. As a new type of dangerous pollutants with high chemical resistance and pronounced biological effects, they accumulate everywhere, often in significant concentrations (μg/L) in ecological environments, food chains, organs of farm animals and humans, and cause an intense response from the aquatic and soil microbiota. Rhodococcus spp. (Actinomycetia class), which occupy a dominant position in polluted ecosystems, stand out among other microorganisms with the greatest variety of degradable pollutants and participate in natural attenuation, are considered as active agents with high transforming and degrading impacts on pharmaceutical compounds. Many representatives of rhodococci are promising as unique sources of specific transforming enzymes, quorum quenching tools, natural products and novel antimicrobials, biosurfactants and nanostructures. The review presents the latest knowledge and current trends regarding the use of Rhodococcus spp. in the processes of pharmaceutical pollutants’ biodegradation, as well as in the fields of biocatalysis and biotechnology for the production of targeted pharmaceutical products. The current literature sources presented in the review can be helpful in future research programs aimed at promoting Rhodococcus spp. as potential biodegraders and biotransformers to control pharmaceutical pollution in the environment.

Bacterial Hydratases Involved in Steroid Side Chain Degradation Have Distinct Substrate Specificities

Actinobacterial MaoC family enoyl coenzyme A (CoA) hydratases catalyze the addition of water across the double bond of CoA esters during steroid side chain catabolism. We determined that heteromeric MaoC type hydratases, exemplified by ChsH1-ChsH2_Mtb of Mycobacterium tuberculosis and CasM-CasO_Rjost from Rhodococcus jostii RHA1, are specific toward a 3-carbon side chain steroid metabolite, consistent with their roles in the last β-oxidation cycle of steroid side chain degradation. Hydratases containing two fused MaoC domains are responsible for the degradation of longer steroid side chains. These hydratases, encoded in the cholesterol degradation gene clusters of M. tuberculosis and R. jostii RHA1, have broad specificity and were able to catalyze the hydration of the 5-carbon side chain of both cholesterol and bile acid metabolites. Surprisingly, the homologous hydratases from the bile acid degradation pathway have low catalytic efficiencies or no activity toward the 5-carbon side chain bile acid metabolites, cholyl-enoyl-CoA, lithocholyl-enoyl-CoA, and chenodeoxycholyl-enoyl-CoA. Instead, these hydratases preferred a cholate metabolite with oxidized steroid rings and a planar ring structure. Together, the results suggest that ring oxidation occurs prior to side chain degradation in the actinobacterial bile acid degradation pathway. IMPORTANCE Characterization of the substrate specificity of hydratases described here will facilitate the development of specific inhibitors that may be useful as novel therapeutics against M. tuberculosis and to metabolically engineer bacteria to produce steroid pharmaceuticals with desired steroid rings and side chain structures.

Rational development of mycobacteria cell factory for advancing the steroid biomanufacturing

Steroidal resource occupies a vital proportion in the pharmaceutical industry attributing to their important therapeutic effects on fertility, anti-inflammatory and antiviral activities. Currently, microbial transformation from phytosterol has become the dominant strategy of steroidal drug intermediate synthesis that bypasses the traditional chemical route. Mycobacterium sp. serve as the main industrial microbial strains that are capable of introducing selective functional modifications of steroidal intermediate, which has become an indispensable platform for steroid biomanufacturing. By reviewing the progress in past two decades, the present paper concentrates mainly on the microbial rational modification aspects that include metabolic pathway editing, key enzymes engineering, material transport pathway reinforcement, toxic metabolic intermediates removal and byproduct reconciliation. In addition, progress on omics analysis and direct genetic manipulation are summarized and classified that may help reform the industrial hosts with more efficiency. The paper provides an insightful present for steroid biomanufacturing especially on the current trends and prospects of mycobacteria.

Biotransformation of Androstenedione by Filamentous Fungi Isolated from Cultural Heritage Sites in the State Tretyakov Gallery

Simple Summary

Microorganisms are able to grow on substrates of the most diverse nature. One of the most practical habitats, in terms of cultural heritage conservation, is fine art objects such as tempera or oil paintings on canvas. Since tempera paints are produced on the basis of egg yolk, which is one of the richest sources of cholesterol in nature (up to 2% of dry weight), and in the process of aging of tempera materials, changes in cholesterol do not affect the core structure of the steroid nucleus, the group of fungi that we have isolated are tempera painting destructors is seen as a promising object for screening for their possible steroid-transforming activities. In this regard, the purpose of our work was to determine the ability to transform pharmaceutically significant steroids with dominant fungi-destructors of tempera paintings, previously isolated in the State Tretyakov Gallery. Consequently, we have demonstrated for the first time that fungi-destructors of tempera paintings have steroid-transforming activity and are promising microorganisms for screening for biotechnologically significant transformations of steroids with further industrial use.

Abstract

The transformation of steroids by microorganisms is widely used in medical biotechnology. A huge group of filamentous fungi is one of the most promising taxa for screening new biocatalytic reactions in order to obtain pharmaceutically significant steroids. In this work, we screened 10 filamentous fungi-destructors of egg tempera for the ability to biotransform androst-4-en-3,17-dione (AD) during cultivation in a liquid nutrient medium or in a buffer solution. These taxonomically unrelated strains, belonging to the classes Eurotiomycetes, Dothideomycetes and Sordariomycetes, are dominant representatives of the microbiome from halls where works of tempera painting are stored in the State Tretyakov Gallery (STG, Moscow, Russia). Since the binder of tempera paints, egg yolk, contains about 2% cholesterol, these degrading fungi appear to be a promising group for screening for steroid converting activity. It turned out that all the studied fungi-destructors are able to transform AD. Some strains showed transformation efficiency close to the industrial strain Curvularia lunata RNCIM F-981. In total, 33 steroids formed during the transformation of AD were characterized, for 19 of them the structure was established by gas chromatography/mass spectrometry analysis. In this work, we have shown for the first time that fungi-destructors of tempera paintings can efficiently transform steroids.

Biotransformation Enables Innovations Toward Green Synthesis of Steroidal Pharmaceuticals

Steroids have been widely used in birth-control, prevention, and treatment of various diseases, representing the largest sector after antibiotics in the global pharmaceutical market. The steroidal active pharmaceutical ingredients (APIs) have been produced via partial synthetic processes first mainly from sapogenins, which was converted into 16-dehydropregnenolone by the famous "Marker Degradation". Traditional mutation and screening, and process engineering have resulted in the industrial production of 4-androstene-3,17-dione (AD), androst-1,4-diene-3,17-dione (ADD), 9α-hydroxy-androsta-4-ene-3,17-dione (9α-OH-AD), and so on, which serve as the key intermediates for the synthesis of steroidal APIs. Recently, genetic and metabolic engineering have generated highly efficient microbial strains for the production of these precursors, leading to the replacement of sapogenins with phytosterols as the starting materials. Further advances in synthetic biology hold promise in the design and construction of microbial cell factories for the industrial production of steroidal intermediates and/or APIs from simple carbon sources such as glucose. Integration of biotransformation into the synthesis of steroidal APIs can greatly reduce the number of reaction steps, achieve lower waste discharge and higher production efficiency, thus enabling a greener steroidal pharmaceutical industry.

Recent progress in strategies for steroid production in yeasts

As essential structural molecules of fungal cell membrane, ergosterol is not only an important component of fungal growth and stress-resistance but also a key precursor for manufacturing steroid drugs of pharmaceutical or agricultural significance. So far, ergosterol biosynthesis in yeast has been elucidated elaborately, and efforts have been made to increase ergosterol production through regulation of ergosterol metabolism and storage. Furthermore, the same intermediates shared by yeasts and animals or plants make the construction of heterologous sterol pathways in yeast a promising approach to synthesize valuable steroids, such as phytosteroids and animal steroid hormones. During these challenging processes, several obstacles have arisen and been combated with great endeavors. This paper reviews recent research progress of yeast metabolic engineering for improving the production of ergosterol and heterologous steroids. The remaining tactics are also discussed.