Steroid 17β-reduction by microorganisms—a review

Direct Microplate Sampling Mass Spectrometry for High-Throughput Screening of Biocatalytic Activity

The development of biocatalysis depends heavily on high-throughput screening (HTS) approaches to uncover engineered enzymes with superior biocatalytic activity. Recent advances in mass spectrometry (MS) enable label-free, high-speed analysis of biocatalytic samples in standard microplates by omitting the chromatographic separation. However, most MS methods need a complicated sampling interface system and face challenges due to biological matrix interferences, which can diminish the sensitivity and reliability. Herein, we established a direct microplate sampling (DMS)-MS technique for HTS of the enzymatic activity of 17β-hydroxysteroid dehydrogenase (17β-HSD) in steroid biocatalysis. The implementation of an open port interface (OPI) probe with a customized ion source for microwell direct insertion sampling and ionization has streamlined the setup, reduced operational complexity, and shortened the analysis time to 0.9-6.5 s/sample. A sample preparation strategy involving derivatization, followed by high-ratio dilution (e.g., 10,000-fold), was further integrated prior to DMS-MS for mitigating ion suppression effects across diverse biological matrices. Ultimately, this workflow, when applied for monitoring multiple steroids in 17β-HSD biocatalytic processes, demonstrated high stability (peak area RSDs < 7%), minimal carryover (<1%), and quantitative accuracy comparable to conventional liquid chromatography (LC) experiments while providing a >150-fold throughput enhancement. After screening a total of 5760 17β-HSD mutants across three different steroid conversion reactions, we identified and verified two new variants with enhanced biocatalytic activities. This study successfully established a DMS-MS-based HTS workflow for microplate screening, providing a simplified, robust, and highly reliable analytical platform for microbial or enzyme engineering projects involving complex biological matrices.

Microbial steroid biotransformation: Regio- and stereo selective 17β-reduction by Priestia aryabhattai

The conversion of 17-oxosteroids to 17β-hydroxysteroids stands as a pivotal process in the synthesis of numerous steroidal drugs and intermediates. This study explored the potential of the strain Priestia aryabhattai (IICT-BC-1279) to catalyze the reduction of the C-17 carbonyl group in androst-4-ene-3,17-dione (AD), resulting in the exclusive production of testosterone (TS) through its 17β-hydroxysteroid dehydrogenase (17β-HSD) activity. Optimal conditions for this reduction were achieved at pH 7.0 and 25 °C, with supplementation of AD as an inducer (0.01 g/L), 1 % Tween 80 (w/v) and ethanol as co-solvent. Under these optimized parameters, 0.5 g/L AD was efficiently converted to TS as a sole product, achieving a yield of > 95 % and diastereomeric excess (d.e) of > 99 % within 48 h. The absence of by-products in this microbial 17β-reduction process simplifies product purification, highlighting the strain's potential as a valuable biocatalyst for this essential transformation. Additionally, the conversion of androsta-1,4-diene-3,17-dione (ADD) to (+)-Boldenone (BD) was studied to explore substrate scope.

Efficient bioremediation of multiple steroid hormones by halotolerant 17β-hydroxysteroid dehydrogenase derived from moderately halophilic Pontibacillus chungwhensis HN14

Steroid hormones exhibit potent endocrine disrupting activity and have been shown to disrupt the equilibrium of aquatic ecosystems and pose a threat to public health through their persistent and carcinogenic effects. Pontibacillus chungwhensis HN14, a moderately halophilic bacterium with the capacity to effectively degrade various polycyclic aromatic hydrocarbons and other organic pollutants, was previously isolated. Additionally, the strain HN14 showed strong environmental adaptability under various environmental stress conditions. In this study, the steroid degradation by strain HN14 was studied for the first time. We demonstrated that strain HN14 could degrade estradiol (E2) to maintain the growth of the strain and could convert E2 to estrone. Additionally, the efficient substrate degradation efficiency of P. chungwhensis HN14 under high salinity and high substrate concentration conditions was demonstrated. Furthermore, a 17β-hydroxysteroid dehydrogenase, 17β-HSD(HN14), was identified in strain HN14. Comparative analysis reveals that 17β-HSD(HN14) shares approximately 38% sequence identity with 17β-HSDx from Rhodococcus sp. P14. In addition, 100 µg of purified 17β-HSD(HN14) could effectively convert about 40% of 0.25 mM of E2 within 1 h period, with an enzyme activity of 17.5 U/mg, and catalyze the dehydrogenation of E2 and testosterone at the C-17 position. The characterization of purified enzyme properties reveals that 17β-HSD(HN14) exhibits exceptional structural robustness and enzymatic efficacy even under high salinity conditions of up to 20%. Overall, this study enhances our comprehension of steroid biodegradation in strain HN14 and contributes novel ideas and theoretical underpinnings for advancing bioremediation technologies targeting steroid pollution in high-saline environments.

Steroid modification by filamentous fungus Drechslera sp.: Focus on 7-hydroxylase and 17β-hydroxysteroid dehydrogenase activities

Fungal strain Drechslera sp. Ph F-34 was shown to modify 3-oxo- and 3-hydroxy steroids of androstane series to form the corresponding allylic 7-alcohols and 17β-reduced derivatives thus evidencing the presence of 7α-, 7β-hydroxylase and 17β-hydroxysteroid dehydrogenase (17β-HSD) activities. The growing mycelium predominantly hydroxylated androsta-1,4-diene-3,17-dione (ADD) at the 7β-position, while much lower 7α-hydroxylation was observed. Along with 7β-hydroxy-ADD and its corresponding 7α-isomer, their respective 17β-alcohols were produced. In this study, transformation of ADD, androst-4-en-17β-ol-3-one (testosterone, TS) and 3β-hydroxyandrost-5-en-17-one (dehydroepiandrosterone, DHEA) by resting mycelium of Drechslera sp. have been estimated in different conditions with regard to the inducibility and functionality of the 17β-HSD and 7-hydroxylase enzyme systems. Steroids of androstane, pregnane and cholane series were evaluated as inducers. The inhibitory analysis was provided using cycloheximide (CHX). Steroids were assayed using TLC and HPLC methods, and the structures were confirmed by mass-spectrometry, ¹H and ¹³C NMR spectroscopy data. 17β-HSD of the mycelium constitutively reduced 17-carbonyl group of ADD and DHEA to form the corresponding 17β-alcohols, namely, androsta-1,4-diene-17β-ol-3-one (1-dehydro-TS), and androst-5-ene-3β,17β-diol. Production of the 7α- and 7β-hydroxylated derivatives depended on the induction conditions. The inducer effect relied on the steroid structure and decreased in the order: DHEA > pregnenolone > lithocholic acid. β-Sitosterol did not induce hydroxylase activity in Drechslera sp. CHX fully inhibited the synthesis of 7-hydroxylase in Drechslera mycelium thus providing selective 17-keto reduction. Results contribute to the diversity of steroid modifying enzymes in fungi and can be used at the development of novel biocatalysts for production of valuable steroid 7(α/β)- and 17β-alcohols.

Efficient One-Step Biocatalytic Multienzyme Cascade Strategy for Direct Conversion of Phytosterol to C-17-Hydroxylated Steroids

Steroidal 17-carbonyl reduction is crucial to the production of natural bioactive steroid medicines, and boldenone (BD) is one of the important C-17-hydroxylated steroids. Although efforts have been made to produce BD through biotransformation, the challenges of the complex transformation process, high substrate costs, and low catalytic efficiencies have yet to be mastered. Phytosterol (PS) is the most widely accepted substrate for the production of steroid medicines due to its similar foundational structure and ubiquitous sources. 17β-Hydroxysteroid dehydrogenase (17βHSD) and its native electron donor play significant roles in the 17β-carbonyl reduction reaction of steroids. In this study, we bridged 17βHSD with a cofactor regeneration strategy in Mycobacterium neoaurum to establish a one-step biocatalytic carbonyl reduction strategy for the efficient biosynthesis of BD from PS for the first time. After investigating different intracellular electron transfer strategies, we rationally designed the engineered strain with the coexpression of 17βhsd and the glucose-6-phosphate dehydrogenase (G6PDH) gene in M. neoaurum. With the establishment of an intracellular cofactor regeneration strategy, the ratio of [NADPH]/[NADP⁺] was maintained at a relatively high level, the yield of BD increased from 17% (in MNR M3M-ayr1_S.c) to 78% (in MNR M3M-ayr1&g6p with glucose supplementation), and the productivity was increased by 6.5-fold. Furthermore, under optimal glucose supplementation conditions, the yield of BD reached 82%, which is the highest yield reported for transformation from PS in one step. This study demonstrated an excellent strategy for the production of many other valuable carbonyl reduction steroidal products from natural inexpensive raw materials. IMPORTANCE Steroid C-17-carbonyl reduction is one of the important transformations for the production of valuable steroidal medicines or intermediates for the further synthesis of steroidal medicines, but it remains a challenge through either chemical or biological synthesis. Phytosterol can be obtained from low-cost residues of waste natural materials, and it is preferred as the economical and applicable substrate for steroid medicine production by Mycobacterium. This study explored a green and efficient one-step biocatalytic carbonyl reduction strategy for the direct conversion of phytosterol to C-17-hydroxylated steroids by bridging 17β-hydroxysteroid dehydrogenase with a cofactor regeneration strategy in Mycobacterium neoaurum. This work has practical value for the production of many valuable hydroxylated steroids from natural inexpensive raw materials.

The catalytic activity of mycelial fungi towards 7-oxo-DHEA - an endogenous derivative of steroidal hormone dehydroepiandrosterone

Seventeen species of fungi belonging to thirteen genera were screened for the ability to carry out the transformation of 7-oxo-DHEA (7-oxo-dehydroepiandrosterone). Some strains expressed new patterns of catalytic activity towards the substrate, namely 16β-hydroxylation (Laetiporus sulphureus AM498), Baeyer-Villiger oxidation of ketone in D-ring to lactone (Fusicoccum amygdali AM258) and esterification of the 3β-hydroxy group (Spicaria divaricata AM423). The majority of examined strains were able to reduce the 17-oxo group of the substrate to form 3β,17β-dihydroxy-androst-5-en-7-one. The highest activity was reached with Armillaria mellea AM296 and Ascosphaera apis AM496 for which complete conversion of the starting material was achieved, and the resulting 17β-alcohol was the sole reaction product. Two strains of tested fungi were also capable of stereospecific reduction of the conjugated 7-keto group leading to 7β-hydroxy-DHEA (Inonotus radiatus AM70) or a mixture of 3β,7α,17β-trihydroxy-androst-5-ene and 3β,7β,17β-trihydroxy-androst-5-ene (Piptoporus betulinus AM39). The structures of new metabolites were confirmed by MS and NMR analysis. They were also examined for their cholinesterase inhibitory activity in an enzymatic-based assay in vitro test.

One-Step Chemo-, Regio- and Stereoselective Reduction of Ketosteroids to Hydroxysteroids over Zr-Containing MOF-808 Metal-Organic Frameworks

Zr-containing MOF-808 is a very promising heterogeneous catalyst for the selective reduction of ketosteroids to the corresponding hydroxysteroids through a Meerwein-Ponndorf-Verley (MPV) reaction. Interestingly, the process leads to the diastereoselective synthesis of elusive 17α-hydroxy derivatives in one step, whereas most chemical and biological transformations produce the 17β-OH compounds, or they require several additional steps to convert 17β-OH into 17α-OH by inverting the configuration of the 17 center. Moreover, MOF-808 is found to be stable and reusable; it is also chemoselective (only keto groups are reduced, even in the presence of other reducible groups such as C=C bonds) and regioselective (in 3,17-diketosteroids only the keto group in position 17 is reduced, while the 3-keto group remains almost intact). The kinetic rate constant and thermodynamic parameters of estrone reduction to estradiol have been obtained by a detailed temperature-dependent kinetic analysis. The results evidence a major contribution of the entropic term, thus suggesting that the diastereoselectivity of the process is controlled by the confinement of the reaction inside the MOF cavities, where the Zr4+ active sites are located.

Relationship between gut microbiota and host-metabolism: Emphasis on hormones related to reproductive function

It has been well recognized that interactions between the gut microbiota and host-metabolism have a proven effect on health. The gut lumen is known for harboring different bacterial communities. Microbial by-products and structural components, which are derived through the gut microbiota, generate a signaling response to maintain homeostasis. Gut microbiota is not only involved in metabolic disorders, but also participates in the regulation of reproductive hormonal function. Bacterial phyla, which are localized in the gut, allow for the metabolization of steroid hormones through the stimulation of different enzymes. Reproductive hormones such as progesterone, estrogen and testosterone play a pivotal role in the successful completion of reproductive events. Disruption in this mechanism may lead to reproductive disorders. Environmental bacteria can affect the metabolism, and degrade steroid hormones and their relevant compounds. This behavior of the bacteria can safely be implemented to eliminate steroidal compounds from a polluted environment. In this review, we summarize the metabolism of steroid hormones on the regulation of gut microbiota and vice-versa, and also examined the significant influence this process has on various events of reproductive function. Altogether, the evidence suggests that steroid hormones and gut microbiota exert a central role in the modification of host bacterial action and impact the reproductive efficiency of animals and humans.

Yeast as a promising heterologous host for steroid bioproduction

With the rapid development of synthetic biology and metabolic engineering technologies, yeast has been generally considered as promising hosts for the bioproduction of secondary metabolites. Sterols are essential components of cell membrane, and are the precursors for the biosynthesis of steroid hormones, signaling molecules, and defense molecules in the higher eukaryotes, which are of pharmaceutical and agricultural significance. In this mini-review, we summarize the recent engineering efforts of using yeast to synthesize various steroids, and discuss the structural diversity that the current steroid-producing yeast can achieve, the challenge and the potential of using yeast as the bioproduction platform of various steroids from higher eukaryotes.

Production aspects of testosterone by microbial biotransformation and future prospects

In human males, TS plays a key role in maintaining health and sexual functioning. Cholesterol acts as a precursor molecule for its biosynthesis. The microbial biotransformation of cholesterol by numerous microbes like bacteria, fungi, yeasts, etc. has led to the synthesis of TS out of human body making it a great example for industrial steroid production due to its therapeutic properties. Biotransformation through microbes is more advantageous over chemical synthesis as it gives higher conversion rates, higher specificity; reaction goes under mild conditions like temperature and neutral pH, thus being an effective alternate to chemical route. Current review focuses on production aspects of TS by microbial biotransformation and its future prospects with recent advancement.

New 6,19-oxidoandrostan derivatives obtained by biotransformation in environmental filamentous fungi cultures

Background

Steroid compounds with a 6,19-oxirane bridge possess interesting biological activities including anticonvulsant and analgesic properties, bacteriostatic activity against Gram-positive bacteria and selective anti-glucocorticoid action, while lacking mineralocorticoid and progestagen activity.

Results

The study aimed to obtain new derivatives of 3β-acetyloxy-5α-chloro-6,19-oxidoandrostan-17-one by microbial transformation. Twelve filamentous fungal strains were used as catalysts, including entomopathogenic strains with specific activity in the transformation of steroid compounds. All selected strains were characterised by high biotransformation capacity for steroid compounds. However, high substrate conversions were obtained in the cultures of 8 strains: Beauveria bassiana KCh BBT, Beauveria caledonica KCh J3.4, Penicillium commune KCh W7, Penicillium chrysogenum KCh S4, Mucor hiemalis KCh W2, Fusarium acuminatum KCh S1, Trichoderma atroviride KCh TRW and Isaria farinosa KCh KW1.1. Based on gas chromatography (GC) and nuclear magnetic resonance (NMR) analyses, it was found that almost all strains hydrolysed the ester bond of the acetyl group. The strain M. hiemalis KCh W2 reduced the carbonyl group additionally. From the P. commune KCh W7 and P. chrysogenum KCh S4 strain cultures a product of D-ring Baeyer–Villiger oxidation was isolated, whereas from the culture of B. bassiana KCh BBT a product of hydroxylation at the 11α position and oxidation of the D ring was obtained. Three 11α-hydroxy derivatives were obtained in the culture of I. farinosa KCh KW1.1: 3β,11α-dihydroxy-5α-chloro-6,19-oxidoandrostan-17-one, 3β,11α,19-trihydroxy-5α-chloro-6,19-oxidoandrostan-17-one and 3β,11α-dihydroxy-5α-chloro-6,19-oxidoandrostan-17,19-dione. They are a result of consecutive reactions of hydrolysis of the acetyl group at C-3, 11α- hydroxylation, then hydroxylation at C-19 and its further oxidation to lactone.

Conclusions

As a result of the biotransformations, seven steroid derivatives, not previously described in the literature, were obtained: 3β-hydroxy-5α-chloro-6,19-oxidoandrostan-17-one, 3β,17α-dihydroxy-5α-chloro-6,19-oxidoandrostane, 3β-hydroxy-5α-chloro-17α-oxa-D-homo-6,19-oxidoandrostan-17-one, 3β,11α-dihydroxy-5α-chloro-17α-oxa-D-homo-6,19-oxidoandrostan-17-one and the three above–mentioned 11α-hydroxy derivatives. This study will allow a better understanding and characterisation of the catalytic abilities of individual microorganisms, which is crucial for more accurate planning of experiments and achieving more predictable results.

Metabolic engineering of Rhodococcus ruber Chol-4: A cell factory for testosterone production

Rhodococcus ruber Chol-4 is a potent steroid degrader that has a great potential as a biotechnological tool. As proof of concept, this work presents testosterone production from 4-androstene-3,17-dione by tailoring innate catabolic enzymes of the steroid catabolism inside the strain. A R. ruber quadruple mutant was constructed in order to avoid the breakage of the steroid nucleus. At the same time, an inducible expression vector for this strain was developed. The 17-ketoreductase gene from the fungus Cochliobolus lunatus was cloned and overexpressed in this vector. The engineered strain was able to produce testosterone from 4-androstene-3,17-dione using glucose for cofactor regeneration with a molar conversion of 61%. It is important to note that 91% of the testosterone was secreted outside the cell after 3 days of cell biotransformation. The results support the idea that Rhodococcus ruber Chol-4 can be metabolically engineered and can be used for the production of steroid intermediates.

A highly efficient step-wise biotransformation strategy for direct conversion of phytosterol to boldenone

Collaborative microbial communities are ubiquitous in nature and exhibit appealing functions for enhanced production of natural products, which provides new possibility for biotechnology development. In this study, we bridged Mycobacterium neoaurum with Pichia pastoris to establish a step-wise biotransformation strategy for efficient biosynthesis of boldenone (BD) from phytosterol (PS). Firstly, the producing strains were rationally designed with overexpression of 3-ketosteroid-Δ1-dehydrogenase (KsdD) and 17β-hydroxysteroid dehydrogenase (17βHSD) in M. neoaurum and P. pastoris, respectively. Then, to shorten the total biotransformation process and provide reducing power, semi-batch fermentation strategy and glucose supplementation strategy were introduced at side-chain degradation stage and carbonyl reduction stage, respectively. Under the optimal transformation conditions, the productivity of BD was increased from 10% to 76% and the total biotransformation process was shortened by 41.7%, which is the shortest among the ever reported. Our results demonstrated an excellent biological strategy for production of many other valuable microbial products from bioresources.

A novel dehydrogenase 17β-HSDx from Rhodococcus sp. P14 with potential application in bioremediation of steroids contaminated environment

Steroids are endocrine disrupting compounds in human and are distributed in various environments. Our previous study showed that a marine bacterium Rhodococcus sp. P14 was able to efficiently degrade one typical steroid estradiol. In this study, we showed that P14 could also use other steroids, including estriol and testosterone, as sole carbon source for growth. Two dehydrogenation products, 16-hydroxestrone and androst-4-ene-3, 17-dione, were detected during estriol and testosterone degradation, respectively. By screening the genome, a short chain dehydrogenase gene was identified and named as 17β-HSDx. Expression of 17β-HSDx was induced in P14 when estriol, estradiol or testosterone was used as single carbon source. In addition, 17β-HSDx was shown to have dehydrogenation ability of transforming estriol to 16-hydroxestrone, estradiol to estrone and testosterone to androst-4-ene-3, 17-dione. This is the first short chain dehydrogenase identified in bacteria with dehydrogenation ability on various steroids substrates. Overall, this study reveals that 17β-HSDx has potential application in the bioremediation of steroids contaminated environment.

Structural basis for inhibition of 17β-hydroxysteroid dehydrogenases by phytoestrogens: The case of fungal 17β-HSDcl

Phytoestrogens are plant-derived compounds that functionally and structurally mimic mammalian estrogens. Phytoestrogens have broad inhibitory activities toward several steroidogenic enzymes, such as the 17β-hydroxysteroid dehydrogenases (17β-HSDs), which modulate the biological potency of androgens and estrogens in mammals. However, to date, no crystallographic data are available to explain phytoestrogens binding to mammalian 17β-HSDs. NADP(H)-dependent 17β-HSD from the filamentous fungus Cochliobolus lunatus (17β-HSDcl) has been the subject of extensive biochemical, kinetic and quantitative structure-activity relationship studies that have shown that the flavonols are the most potent inhibitors. In the present study, we investigated the structure-activity relationships of the ternary complexes between the holo form of 17β-HSDcl and the flavonols kaempferol and 3,7-dihydroxyflavone, in comparison with the isoflavones genistein and biochanin A. Crystallographic data are accompanied by kinetic analysis of the inhibition mechanisms for six flavonols (3-hydroxyflavone, 3,7-dihydroxyflavone, kaempferol, quercetin, fisetin, myricetin), one flavanone (naringenin), one flavone (luteolin), and two isoflavones (genistein, biochanin A). The kinetics analysis shows that the degree of hydroxylation of ring B significantly influences the overall inhibitory efficacy of the flavonols. A distinct binding mode defines the interactions between 17β-HSDcl and the flavones and isoflavones. Moreover, the complex with biochanin A reveals an unusual binding mode that appears to account for its greater inhibition of 17β-HSDcl with respect to genistein. Overall, these data provide a blueprint for identification of the distinct molecular determinants that underpin 17β-HSD inhibition by phytoestrogens.

Regio- and stereoselective reduction of 17-oxosteroids to 17β-hydroxysteroids by a yeast strain Zygowilliopsis sp. WY7905

The reduction of 17-oxosteroids to 17β-hydroxysteroids is one of the important transformations for the preparation of many steroidal drugs and intermediates. The strain Zygowilliopsis sp. WY7905 was found to catalyze the reduction of C-17 carbonyl group of androst-4-ene-3,17-dione (AD) to give testosterone (TS) as the sole product by the constitutive 17β-hydroxysteroid dehydrogenase (17β-HSD). The optimal conditions for the reduction were pH 8.0 and 30°C with supplementing 10g/l glucose and 1% Tween 80 (w/v). Under the optimized transformation conditions, 0.75g/l AD was reduced to a single product TS with >90% yield and >99% diastereomeric excess (de) within 24h. This strain also reduced other 17-oxosteroids such as estrone, 3β-hydroxyandrost-5-en-17-one and norandrostenedione, to give the corresponding 17β-hydroxysteroids, while the C-3 and C-20 carbonyl groups were intact. The absence of by-products in this microbial 17β-reduction would facilitate the product purification. As such, the strain might serve as a useful biocatalyst for this important transformation.

Engineering Mycobacterium smegmatis for testosterone production

A new biotechnological process for the production of testosterone (TS) has been developed to turn the model strain Mycobacterium smegmatis suitable for TS production to compete with the current chemical synthesis procedures. We have cloned and overexpressed two genes encoding microbial 17β‐hydroxysteroid: NADP 17‐oxidoreductase, from the bacterium Comamonas testosteroni and from the fungus Cochliobolus lunatus. The host strains were M. smegmatis wild type and a genetic engineered androst‐4‐ene‐3,17‐dione (AD) producing mutant. The performances of the four recombinant bacterial strains have been tested both in growing and resting‐cell conditions using natural sterols and AD as substrates respectively. These strains were able to produce TS from sterols or AD with high yields. This work represents a proof of concept of the possibilities that offers this model bacterium for the production of pharmaceutical steroids using metabolic engineering approaches.

The Fungus Trichoderma Regulates Submerged Conidiation Using the Steroid Pregnenolone

In previous work, we evolved a population of Trichoderma citrinoviride in liquid cultures to speed up its asexual development cycle. The evolved population, called T-6, formed conidia 3 times sooner and in >1000-fold greater numbers. Here, we identify the steroid pregnenolone as a molecular signal for this different behavior. Media in which the ancestral T. citrinoviride population was grown (called ancestral spent media) contained a submerged conidiation inhibitor. Growing the evolved population T-6 in ancestral spent media eliminated the abundant formation of conidia. This inhibition depended on the amount and age of the ancestral spent medium and the time that the ancestral spent medium was added to the T-6 culture. Fractionation of the ancestral spent medium identified a hydrophobic inhibiting compound with a molecular weight less than 2000 g/mol. A combination of GC-MS, ELISA, and reaction with cholesterol oxidase identified it as pregnenolone. The addition of pregnenolone to cultures of T-6 inhibited submerged conidiation by inhibiting formation of conidiophores, while 10 other analogous steroids did not. Pregnenolone also inhibited submerged conidiation of Fusarium graminearum PH-1, a plant pathogen that causes head blight in wheat and barley. This identification of steroids as signal molecules in fungi creates opportunities to disrupt this signaling to control fungal behavior.

Sex differences in the gut microbiome-brain axis across the lifespan

In recent years, the bidirectional communication between the gut microbiome and the brain has emerged as a factor that influences immunity, metabolism, neurodevelopment and behaviour. Cross-talk between the gut and brain begins early in life immediately following the transition from a sterile in utero environment to one that is exposed to a changing and complex microbial milieu over a lifetime. Once established, communication between the gut and brain integrates information from the autonomic and enteric nervous systems, neuroendocrine and neuroimmune signals, and peripheral immune and metabolic signals. Importantly, the composition and functional potential of the gut microbiome undergoes many transitions that parallel dynamic periods of brain development and maturation for which distinct sex differences have been identified. Here, we discuss the sexually dimorphic development, maturation and maintenance of the gut microbiome-brain axis, and the sex differences therein important in disease risk and resilience throughout the lifespan.

Rates and product identification for trenbolone acetate metabolite biotransformation under aerobic conditions

Trenbolone acetate metabolites are endocrine-active contaminants discharged into the aquatic environment in runoff from agricultural fields, rangelands, and concentrated animal feeding operations. To investigate the environmental fate of these compounds and their biotransformation mechanisms, the authors used inocula from a variety of different water sources and dosed biologically active microcosms with approximately 1400 ng/L of trenbolone acetate metabolites, including 17β-trenbolone, trendione, and 17α-trenbolone. To investigate aerobic biotransformation rates and interconversions between known trenbolone acetate metabolites, gas chromatography-tandem mass spectrometry was used to measure concentrations and assess product distributions as a function of time. High-resolution liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to characterize novel transformation products and potential transformation pathways. Kinetic analysis yields observed half-lives of approximately 0.9 d, 1.3 d, and 2.2 d for 17β-trenbolone, trendione, and 17α-trenbolone, respectively, at 20 °C, although colder conditions increased half-lives to 8.5 d and biphasic transformation was observed. Relative to reported faster attenuation rates in soils, trenbolone acetate metabolites are likely more persistent in aqueous systems. Product distributions indicate an enzymatic preference for biotransformation between trendione and 17β-trenbolone. The LC-MS/MS characterization indicates dehydrogenation products as the major detectable products and demonstrates that major structural elements responsible for bioactivity in steroids are likely retained during biotransformation.

Influence of temperature on nucleus degradation of 4-androstene-3, 17-dione in phytosterol biotransformation by Mycobacterium sp

One of the steroid intermediates, 4-androstene-3, 17-dione (AD), in the biotransformation of phytosterols is valuable for the production of steroid medicaments. However, its degradation during the conversion process is one of the main obstacles to obtain high yields. In this study, the effect of temperature on nucleus degradation during microbial biotransformation of phytosterol was investigated. The results indicated that microbial degradation of phytosterol followed the AD-ADD-'9-OH-ADD' pathway, and that two important reactions involved in nucleus degradation, conversions of AD to ADD and ADD to 9-OH-ADD, were inhibited at 37°C. With a change in the culture temperature from 30 to 37°C, nucleus degradation was reduced from 39·9% to 17·6%, due to inhibition of the putative KstD and Ksh. These results suggested a simple way to decrease the nucleus degradation in phytosterol biotransformation and a new perspective on the possibilities of modifying the metabolism of strains used in industrial applications.

SIGNIFICANCE AND IMPACT OF THE STUDY

Nucleus degradation of products is one of the main problems encountered during phytosterol biotransformation. To solve this problem, the effect of temperature on nucleus degradation was investigated in the industrial production of steroid intermediates. The results are also helpful to the genetic modification of sterol-producing strains.

Luffa cylindrica and phytosterols bioconversion: from shake flask to jar bioreactor

Bioconversion of lipophilic compounds poorly soluble in water, such as sterols, required the use of chemicals and solubilizing agents. On the other hand, it was shown that immobilization of Mycobacterium species on the dried fruit of Luffa cylindrica (DFLC) allows a close interaction between immobilized cells and cholesterol particles and increases by then the product’s yield. In this work, the use of DFLC in a 5-l jar bioreactor with phytosterols mixture (1 g/l) as substrate was assessed without addition of any chemicals or solubilizing agents. DFLC increased by a factor of four the volumetric productivity of androstenones (0.08 g/l day). Products were accumulated in the aqueous medium while substrates remained on the fibers of DFLC. This observation lets envisage a green semi-continuous process of androstenone production. DFLC has no influence on cell growth, and is moreover natural, inexpensive, non-toxic, and mechanically strong.

Role of sex steroid hormones in bacterial-host interactions

Sex steroid hormones play important physiological roles in reproductive and nonreproductive tissues, including immune cells. These hormones exert their functions by binding to either specific intracellular receptors that act as ligand-dependent transcription factors or membrane receptors that stimulate several signal transduction pathways. The elevated susceptibility of males to bacterial infections can be related to the usually lower immune responses presented in males as compared to females. This dimorphic sex difference is mainly due to the differential modulation of the immune system by sex steroid hormones through the control of proinflammatory and anti-inflammatory cytokines expression, as well as Toll-like receptors (TLRs) expression and antibody production. Besides, sex hormones can also affect the metabolism, growth, or virulence of pathogenic bacteria. In turn, pathogenic, microbiota, and environmental bacteria are able to metabolize and degrade steroid hormones and their related compounds. All these data suggest that sex steroid hormones play a key role in the modulation of bacterial-host interactions.

Microbial steroid transformations: current state and prospects

Studies of steroid modifications catalyzed by microbial whole cells represent a well-established research area in white biotechnology. Still, advances over the last decade in genetic and metabolic engineering, whole-cell biocatalysis in non-conventional media, and process monitoring raised research in this field to a new level. This review summarizes the data on microbial steroid conversion obtained since 2003. The key reactions of structural steroid functionalization by microorganisms are highlighted including sterol side-chain degradation, hydroxylation at various positions of the steroid core, and redox reactions. We also describe methods for enhancement of bioprocess productivity, selectivity of target reactions, and application of microbial transformations for production of valuable pharmaceutical ingredients and precursors. Challenges and prospects of whole-cell biocatalysis applications in steroid industry are discussed.

Steroid-transforming enzymes in fungi

Fungal species are a very important source of many different enzymes, and the ability of fungi to transform steroids has been used for several decades in the production of compounds with a sterane skeleton. Here, we review the characterised and/or purified enzymes for steroid transformations, dividing them into two groups: (i) enzymes of the ergosterol biosynthetic pathway, including data for, e.g. ERG11 (14α-demethylase), ERG6 (C-24 methyltransferase), ERG5 (C-22 desaturase) and ERG4 (C-24 reductase); and (ii) the other steroid-transforming enzymes, including different hydroxylases (7α-, 11α-, 11β-, 14α-hydroxylase), oxidoreductases (5α-reductase, 3β-hydroxysteroid dehydrogenase/isomerase, 17β-hydroxysteroid dehydrogenase, C-1/C-2 dehydrogenase) and C-17-C-20 lyase. The substrate specificities of these enzymes, their cellular localisation, their association with protein super-families, and their potential applications are discussed. Article from a special issue on steroids and microorganisms.

Insights into subtle conformational differences in the substrate-binding loop of fungal 17β-hydroxysteroid dehydrogenase: a combined structural and kinetic approach

The 17β-HSD (17β-hydroxysteroid dehydrogenase) from the filamentous fungus Cochliobolus lunatus (17β-HSDcl) is a NADP(H)-dependent enzyme that preferentially catalyses the interconversion of inactive 17-oxo-steroids and their active 17β-hydroxy counterparts. 17β-HSDcl belongs to the SDR (short-chain dehydrogenase/reductase) superfamily. It is currently the only fungal 17β-HSD member that has been described and represents one of the model enzymes of the cP1 classical subfamily of NADPH-dependent SDR enzymes. A thorough crystallographic analysis has been performed to better understand the structural aspects of this subfamily and provide insights into the evolution of the HSD enzymes. The crystal structures of the 17β-HSDcl apo, holo and coumestrol-inhibited ternary complex, and the active-site Y167F mutant reveal subtle conformational differences in the substrate-binding loop that probably modulate the catalytic activity of 17β-HSDcl. Coumestrol, a plant-derived non-steroidal compound with oestrogenic activity, inhibits 17β-HSDcl [IC50 2.8 μM; at 100 μM substrate (4-oestrene-3,17-dione)] by occupying the putative steroid-binding site. In addition to an extensive hydrogen-bonding network, coumestrol binding is stabilized further by π–π stacking interactions with Tyr212. A stopped-flow kinetic experiment clearly showed the coenzyme dissociation as the slowest step of the reaction and, in addition to the low steroid solubility, it prevents the accumulation of enzyme–coenzyme–steroid ternary complexes.

THE BIOTRANSFORMATION, BIODEGRADATION, AND BIOREMEDIATION OF ORGANIC COMPOUNDS BY MICROALGAE(1)

Rapid growth in the biotechnological industry and production has put tremendous pressure on the biological methods that may be used according to the guidelines of green chemistry. However, despite continuing dramatic increases in published research on organic biotransformation by microorganisms, more research exists with microalgae. Our efforts in transforming chemicals such as organic compounds for the production of functionalized products help to lessen the environmental effects of organic synthesis. These biotransformations convert organic contaminants to obtain carbon or energy for growth or as cosubstrates. This review aims to focus on the potential of microalgae in transformation, conversion, remediation, accumulation, degradation, and synthesis of various organic compounds. However, these technologies have the ability to provide the most efficient and environmentally safe approach for inexpensive biotransforming of a variety of organic contaminants, which are most industrial residues. In addition, the recent advances in microalgal bioactivity were discussed.

Isolation and bioaugmentation of an estradiol-degrading bacterium and its integration into a mature biofilm

Bioaugmentation can alter the potential activity as well as the composition of the naturally occurring microbial biota during bioremediation of a contaminated site. The focus of the current study is the pollutant 17β-estradiol (E2), which can cause endocrine effects and is potentially harmful to aquatic biota and to public health. The community composition and function of biofilms, originating from a wetland system, as affected by augmentation of an estradiol-degrading bacterium (EDB-LI1) under different conditions, were investigated. EDB-LI1 inoculation into biofilm from two wetland ponds representing early and advanced water treatment stages, respectively, yielded three significant observations, as follows: (i) EDB-LI1, enriched from a biofilm of a constructed wetland wastewater treatment system, was detected (by quantitative PCR [qPCR] analysis) in this environment in the augmented biofilm only; (ii) the augmented biofilm acquired the ability to remove estradiol; and (iii) the bacterial community composition (analyzed by PCR-denaturing gradient gel electrophoresis [DGGE]) of the augmented biofilm differed from that of the control biofilm. Furthermore, EDB-LI1 bioaugmentation showed a higher level of removal of estradiol with biofilms that originated from the advanced-treatment-stage wetland pond than those from the early-treatment-stage pond. Hence, the bioaugmentation efficiency of EDB-LI1 depends on both the quality of the feed water and the microbial community composition in the pond.

Microbial transformation of 3β-acetoxypregna-5,16-diene-20-one by Penicillium citrinum

The biotransformation of 3β-acetoxypregna-5,16-diene-20-one (1) by using a filamentous fungus Penicillium citrinum resulted in the production of four metabolites 2-5. The structures of these compounds were elucidated by different spectroscopic analysis (1D- and 2D-NMR) and HR-ESI-MS as 3β,7β-dihydroxy-pregn-5,16(17)-dien-20-one (2), 3β-hydroxy-7α-methoxy-pregn-5,16(17)-dien-20-one (3), 3β,7β,11α-trihydroxy-pregn-5,16(17)-dien-20-one (4), and a known 3β,7α-dihydroxy-pregn-5,16(17)-dien-20-one (5). The 7-O-methylation is a novel reaction in the field of microbial transformation of pregnane steroids.

Fate of endocrine-active compounds during municipal biosolids treatment: a review

For two decades, the fates of endocrine-disrupting compounds (EDCs) across various wastewater treatment processes have been studied using chemical and in vitro bioassay measurements. In comparison, little work has been conducted to track the fates of EDCs during municipal biosolids stabilization, particularly using bioassay approaches. This leads to knowledge gaps with respect to understanding which single or combined biosolid treatments facilitate EDC removal, and what the total endocrine-active potency of treated biosolids might be. These unknowns in turn heighten public opposition and distrust of biosolids reuse applications. This review aims to summarize what is currently known regarding EDC removal during commonly used full-scale biosolids treatment processes and highlights analytical challenges that are relevant when in vitro bioassays and chemical analyses are applied to biosolids samples.

Anaerobic testosterone degradation in Steroidobacter denitrificans--identification of transformation products

The transformation of the androgenic steroid testosterone by gammaproteobacterium Steroidobacter denitrificans was studied under denitrifying conditions. For the first time, growth experiments showed that testosterone was mineralized under consumption of nitrate and concurrent biomass production. Experiments with cell suspensions using [4-(14)C]-testosterone revealed the intermediate production of several transformation products (TPs). Characterisation of ten TPs was carried out by means of HPLC coupled to high resolution mass spectrometry with atmospheric pressure chemical ionization as well as (1)H and (13)C NMR spectroscopy. 3beta-hydroxy-5alpha-androstan-17-one (trans-androsterone) was formed in the highest amount followed by 5alpha-androstan-3,17-dione. The data suggests that several dehydrogenation and hydrogenation processes take place concurrently in ring A and D because no consistent time-resolved pattern of TP peaks was observed and assays using 2 TPs as substrates resulted in essentially the same TPs. The further transformation of testosterone in S. denitrificans seems to be very efficient and fast without formation of detectable intermediates.

Physico-chemical pre-treatment and biotransformation of wastewater and wastewater sludge--fate of bisphenol A

Bisphenol A (BPA), an endocrine disrupting compound largely used in plastic and paper industry, ends up in aquatic systems via wastewater treatment plants (WWTPs) among other sources. The identification and quantification of BPA in wastewater (WW) and wastewater sludge (WWS) is of major interest to assess the endocrine activity of treated effluent discharged into the environment. Many treatment technologies, including various pre-treatment methods, such as hydrolysis, Fenton oxidation, peroxidation, ultrasonication and ozonation have been developed in order to degrade BPA in WW and WWS and for the production of WWS based value-added products (VAPs). WWS based VAPs, such as biopesticides, bioherbicides, biofertilizers, bioplastics and enzymes are low cost biological alternatives that can compete with chemicals or other cost intensive biological products in the current markets. However, this field application is disputable due to the presence of these organic compounds which has been discussed with a perspective of simultaneous degradation. The pre-treatment produces an impact on rheology as well as value-addition which has been reviewed in this paper. Various analytical techniques available for the detection of BPA in WW and WWS are also discussed. Presence of heavy metals and possible thermodynamical behavior of the compound in WW and WWS can have major impact on BPA removal, which is also included in the review.

Microbial transformation of phytosterol in corn flour and soybean flour to 4-androstene-3,17-dione by Fusarium moniliforme Sheld

A strain that was capable of transforming the phytosterol in corn flour and soybean flour was isolated from soil and identified as Fusarium moniliforme Sheld. The main transformation product was purified by high performance liquid chromatography (HPLC), and was characterized by nuclear magnetic resonance (NMR), mass spectrum (MS), and infrared spectrum (IR). The results indicated that the product was 4-androstene-3,17-dione (AD). The production of AD was increased with the increase of initial concentration of corn flour while the yield of AD was decreased. The yield of AD was lower in the media with only soybean flour. Sulfate-phosphate-ferric method (SPF) was first used for determination of the total phytosterol content in corn flour or soybean flour. The measured value by SPF method matched reasonably well with that by HPLC, which indicated the validity of SPF method.

Pre-treatment and bioconversion of wastewater sludge to value-added products--fate of endocrine disrupting compounds

Development of processes for the production of value added products (VAPs), such as biopesticides, microbial inoculants or industrial enzymes through biotransformation of raw or pre-treated wastewater sludge (WWS) has undergone a substantial progress over the last decade. WWS based VAPs are low cost biological alternatives that can compete with chemicals or other cost intensive biological products in the current markets. However, when WWS is used as a raw material for VAPs production, questions still remains on the persistence of organic pollutants within the biotransformed WWS, especially, endocrine disrupting compounds (EDCs) and the production of their toxic intermediates. WWS pre-treatment prior to biotransformation as well as the microbial strains used for biotransformation can possibly remove these organic pollutants. The literature findings concerning the impact of WWS pre-treatment and value added products on EDCs removal are reviewed in this paper. The microbial potential to degrade or detoxify EDCs and toxic intermediates concomitant with value-addition is also discussed. The concept of obtaining EDCs free-WWS based VAPs and simultaneously achieving the objective of pollution control is presented.