Efficient production of androstenedione by repeated batch fermentation in waste cooking oil media through regulating NAD+/NADH ratio and strengthening cell vitality of Mycobacterium neoaurum

Enhancement of Biological Nitrogen Removal System Resilience to Chronic Exposure of Zinc Oxide Nanoparticles by Quorum Sensing Modulation: Physiochemical, Microbial, and Metabolic Insights

The effects of three typical N-acyl-homoserine lactones (AHLs) on the tolerance of biological nitrogen removal (BNR) system to chronic exposure of zinc oxide nanoparticles (NPs) were investigated. C4-HSL successfully delayed the crash time of nitrogen removal performances in the NP-stressed system, while C6-HSL and C10-HSL maintained total nitrogen removal efficiencies throughout the 90-day NP exposure. All three AHLs increased NPs' contents captured in extracellular polymeric substances, alleviating membrane damage and preserving floc structure. The activities of tricarboxylic acid cycle-related enzymes and the relative abundances of BNR-related functional genes and genera were significantly enhanced. Besides, C6-HSL and C10-HSL augmented antioxidant enzyme activities and the abundances of functional genes and metabolites related to antioxidation, flagellar assembly, and chemotaxis, which synergistically reduced the reactive oxygen species' excessive accumulation. The tested AHLs effectively enhanced BNR systems' tolerance to chronic NP exposure, providing inspiration for quorum sensing applications in emerging contaminant removal.

High-efficiency bioconversion of phytosterol to bisnoralcohol by metabolically engineered Mycobacterium neoaurum in a micro-emulsion system

21-Hydroxy-20-methylpregn-4-en-3-one (4-HBC, bisnoralcohol) is a crucial intermediate for the synthesis of steroidal drugs. Significant challenges including by-products formation and poor substrate solubility were still confronted in its main synthetic route by microbial conversion from phytosterol. Construction of a direct bioconversion pathway to 4-HBC and an efficient substrate emulsion system is therefore urgently required. In this study, three novel isoenzymes of 3-ketosteroid-Δ1-dehydrogenase (KstD) and 3-ketosteroid 9α-hydroxylase (KsH) in Mycobacterium neoaurum were excavated and identified as KstD4, KstD5, and KsHA3. A strain capable of fully directing the synthesis of 4-HBC was metabolically engineered via serial genetic deletion combined with enhanced expression of cholesterol oxidase (ChOx2) and enoyl-CoA hydratase (EchA19). Moreover, a micro-emulsion system combined with soybean oil and hydroxypropyl-β-cyclodextrin improved substrate solubility and bioavailability. In batch fermentation, molar yield of 96.7% with 39.5 g L-1 4-HBC was obtained from 50 g L-1 phytosterol. Our findings demonstrate the potential for industrial-scale biosynthesis of 4-HBC.

Surfactant-mediated bio-manufacture: A unique strategy for promoting microbial biochemicals production

Biochemicals are widely used in the medicine and food industries and are more efficient and safer than synthetic chemicals. The amphipathic surfactants can interact with the microorganisms and embed the extracellular metabolites, which induce microbial metabolites secretion and biosynthesis, performing an attractive prospect of promoting the biochemical production. However, the commonness and differences of surfactant-mediated bio-manufacture in various fields are largely unexplored. Accordingly, this review comprehensively summarized the properties of surfactants, different application scenarios of surfactant-meditated bio-manufacture, and the mechanism of surfactants increasing metabolites production. Various biochemical productions such as pigments, amino acids, and alcohols could be enhanced using the cloud point and the micelles of surfactants. Besides, the amphiphilicity of surfactants also promoted the utilization of fermentation substrates, especially lignocellulose and waste sludge, by microorganisms, indirectly increasing the metabolites production. The increase in target metabolites production was attributed to the surfactants changing the permeability and composition of the cell membrane, hence improving the secretion ability of microorganisms. Moreover, surfactants could regulate the energy metabolism, the redox state and metabolic flow in microorganisms, which induced target metabolites synthesis. This review aimed to broaden the application fields of surfactants and provide novel insights into the production of microbial biochemicals.

Multi-Omics Study on Molecular Mechanisms of Single-Atom Fe-Doped Two-Dimensional Conjugated Phthalocyanine Framework for Photocatalytic Antibacterial Performance

Currently, photocatalysis of the two-dimensional (2D) conjugated phthalocyanine framework with a single Fe atom (CPF-Fe) has shown efficient photocatalytic activities for the removal of harmful effluents and antibacterial activity. Their photocatalytic mechanisms are dependent on the redox reaction-which is led by the active species generated from the photocatalytic process. Nevertheless, the molecular mechanism of CPF-Fe antimicrobial activity has not been sufficiently explored. In this study, we successfully synthesized CPF-Fe with great broad-spectrum antibacterial properties under visible light and used it as an antibacterial agent. The molecular mechanism of CPF-Fe against Escherichia coli and Salmonella enteritidis was explored through multi-omics analyses (transcriptomics and metabolomics correlation analyses). The results showed that CPF-Fe not only led to the oxidative stress of bacteria by generating large amounts of h+ and ROS but also caused failure in the synthesis of bacterial cell wall components as well as an osmotic pressure imbalance by disrupting glycolysis, oxidative phosphorylation, and TCA cycle pathways. More surprisingly, CPF-Fe could disrupt the metabolism of amino acids and nucleic acids, as well as inhibit their energy metabolism, resulting in the death of bacterial cells. The research further revealed the antibacterial mechanism of CPF-Fe from a molecular perspective, providing a theoretical basis for the application of CPF-Fe photocatalytic antibacterial nanomaterials.

Rerouting phytosterol degradation pathway for directed androst-1,4-diene-3,17-dione microbial bioconversion

Steroid-based drugs are now mainly produced by the microbial transformation of phytosterol, and a two-step bioprocess is adopted to reach high space-time yields, but byproducts are frequently observed during the bioprocessing. In this study, the catabolic switch between the C19- and C22-steroidal subpathways was investigated in resting cells of Mycobacterium neoaurum NRRL B-3805, and a dose-dependent transcriptional response toward the induction of phytosterol with increased concentrations was found in the putative node enzymes including ChoM2, KstD1, OpccR, Sal, and Hsd4A. Aldolase Sal presented a dominant role in the C22 steroidal side-chain cleavage, and the byproduct was eliminated after sequential deletion of opccR and sal. Meanwhile, the molar yield of androst-1,4-diene-3,17-dione (ADD) was increased from 59.4 to 71.3%. With the regard of insufficient activity of rate-limiting enzymes may also cause byproduct accumulation, a chromosomal integration platform for target gene overexpression was established supported by a strong promoter L2 combined with site-specific recombination in the engineered cell. Rate-limiting steps of ADD bioconversion were further characterized and overcome. Overexpression of the kstD1 gene further strengthened the bioconversion from AD to ADD. After subsequential optimization of the bioconversion system, the directed biotransformation route was developed and allowed up to 82.0% molar yield with a space-time yield of 4.22 g·L-1·day-1. The catabolic diversion elements and the genetic overexpression tools as confirmed and developed in present study offer new ideas of M. neoaurum cell factory development for directed biotransformation for C19- and C22-steroidal drug intermediates from phytosterol. KEY POINTS: • Resting cells exhibited a catabolic switch between the C19- and C22-steroidal subpathways. • The C22-steroidal byproduct was eliminated after sequential deletion of opccR and sal. • Rate-limiting steps were overcome by promoter engineering and chromosomal integration.

Effect of antibiotics on the performance of moving bed biofilm reactor for simultaneous removal of nitrogen, phosphorus and copper(II) from aquaculture wastewater

Co-existence of NO3--N, antibiotics, phosphorus (P), and Cu2+ in aquaculture wastewater has been frequently detected, but simultaneous removal and relationship between enzyme and pollutants removal are far from satisfactory. In this study, simultaneous removal of NO3--N, P, antibiotics, and Cu2+ by moving bed biofilm reactor (MBBR) was established. About 95.51 ± 3.40% of NO3--N, 61.24 ± 3.51% of COD, 18.74 ± 1.05% of TP, 88% of Cu2+ were removed synchronously in stage I, and antibiotics removal in stages I-IV was 73.00 ± 1.32%, 79.53 ± 0.88%, 51.07 ± 3.99%, and 33.59 ± 2.73% for tetracycline (TEC), oxytetracycline (OTC), chlortetracycline hydrochloride (CTC), sulfamethoxazole (SMX), respectively. The removal kinetics and toxicity of MBBR effluent were examined, indicating that the first order kinetic model could better reflect the removal of NO3--N, TN, and antibiotics. Co-existence of multiple antibiotics and Cu2+ was the most toxicity to E. coli growth. Key enzyme activity, reactive oxygen species (ROS) level, and its relationship with TN removal were investigated. The results showed that enzymes activities were significantly different under the co-existence of antibiotics and Cu2+. Meanwhile, different components of biofilm were extracted and separated, and enzymatic and non-enzymatic effects of biofilm were evaluated. The results showed that 70.00%- 94.73% of Cu2+ was removed by extracellular enzyme in stages I-V, and Cu2+ removal was mainly due to the action of extracellular enzyme. Additionally, microbial community of biofilm was assessed, showing that Proteobacteria, Bacteroidetes, and Gemmatimonadetes played an important role in the removal of NO3--N, Cu2+, and antibiotics at the phylum level. Finally, chemical bonds of attached and detached biofilm were characterized by X-ray photoelectron spectroscopy (XPS), and effect of nitrogen (N) and P was proposed under the co-existence of antibiotics and Cu2+. This study provides a theoretical basis for further exploring the bioremediation of NO3--N, Cu2+, and antibiotics in aquaculture wastewater.

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.

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.

Biotransformation of grease waste into fatty acid by Penicillium chrysogenum SNP5 through media engineering and artificial neural network

Degradation of grease waste remains a challenging task. Current work deals with the biotransformation of grease waste into fatty acids under submerged fermentation using Penicillium chrysogenum SNP5 through media formulation and artificial neural network (ANN). Fermentation media was formulated to ameliorate the uptake of hydrocarbon by enhancing alkane hydroxylase (AlkB) activity, extracellular release of fatty acids and inhibiting beta-oxidation of fatty acid by regulating transketolase. Further, the process parameters of fermentation were optimized through Artificial Neural Network (ANN) using three critical variables viz; inoculum size (spores/ml), pH, and incubation time (days) while media engineering was done with the optimal supplementation of various medium components such as glucose, YPD, MnSO₄, tetrahydrobiopterin (THB) and phloretin. The maximum conversion of 66.5% of grease waste into fatty acid was achieved at optimum conditions: inoculums size 3.36 × 10⁷ spores/ml, incubation time 11.5 days, pH 7.2 along with formulated media composed of 1% grease in czapek-dox medium supplemented with 55.5 mM glucose, 0.5% YPD, 16.6 mM hexadecane, 1 mM MnSO₄, 1 mM THB, and 1 mM phloretin. The presence of long-chain fatty acids in purified extracts such as oleic acid and octadecanoic acid as end products has valued the evolved process as another source of alternative fuel.

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.

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 .

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 Phytosterols into Androstenedione—A Technological Prospecting Study

Androstenedione (AD) is a key intermediate in the body’s steroid metabolism, used as a precursor for several steroid substances, such as testosterone, estradiol, ethinyl estradiol, testolactone, progesterone, cortisone, cortisol, prednisone, and prednisolone. The world market for AD and ADD (androstadienedione) exceeds 1000 tons per year, which stimulates the pharmaceutical industry’s search for newer and cheaper raw materials to produce steroidal compounds. In light of this interest, we aimed to investigate the progress of AD biosynthesis from phytosterols by prospecting scientific articles (Scopus, Web of Science, and Google Scholar databases) and patents (USPTO database). A wide variety of articles and patents involving AD and phytosterol were found in the last few decades, resulting in 108 relevant articles (from January 2000 to December 2021) and 23 patents of interest (from January 1976 to December 2021). The separation of these documents into macro, meso, and micro categories revealed that most studies (articles) are performed in China (54.8%) and in universities (76%), while patents are mostly granted to United States companies. It also highlights the fact that AD production studies are focused on “process improvement” techniques and on possible modifications of the “microorganism” involved in biosynthesis (64 and 62 documents, respectively). The most-reported “process improvement” technique is “chemical addition” (40%), which means that the addition of solvents, surfactants, cofactors, inducers, ionic liquids, etc., can significantly increase AD production. Microbial genetic modifications stand out in the “microorganism” category because this strategy improves AD yield considerably. These documents also revealed the main aspects of AD and ADD biosynthesis: Mycolicibacterium sp. (basonym: Mycobacterium sp.) (40%) and Mycolicibacterium neoaurum (known previously as Mycobacterium neoaurum) (32%) are the most recurrent species studied. Microbial incubation temperatures can vary from 29 °C to 37 °C; incubation can last from 72 h to 14 days; the mixture is agitated at 140 to 220 rpm; vegetable oils, mainly soybean, can be used as the source of a mixture of phytosterols. In general, the results obtained in the present technological prospecting study are fundamental to mapping the possibilities of AD biosynthesis process optimization, as well as to identifying emerging technologies and methodologies in this scenario.

Identification of a novel cytochrome P450 17A1 enzyme and its molecular engineering

Progesterone-17α-hydroxylase (CYP17A) could transform progesterone to 17α-hydroxyprogesterone (17-HP).

Production of 9,21-dihydroxy-20-methyl-pregna-4-en-3-one from phytosterols in Mycobacterium neoaurum by modifying multiple genes and improving the intracellular environment

Background

Steroid drugs are essential for disease prevention and clinical treatment. However, due to intricated steroid structure, traditional chemical methods are rarely implemented into the whole synthetic process for generating steroid intermediates. Novel steroid drug precursors and their ideal bacterial strains for industrial production have yet to be developed. Among these, 9,21-dihydroxy-20-methyl-pregna-4-en-3-one (9-OH-4-HP) is a novel steroid drug precursor, suitable for the synthesis of corticosteroids. In this study, a combined strategy of blocking Δ¹-dehydrogenation and the C19 pathway as well as improving the intracellular environment was investigated to construct an effective 9-OH-4-HP-producing strain.

Results

The Δ¹-dehydrogenation-deficient strain of wild-type Mycobacterium neoaurum DSM 44074 produces 9-OH-4-HP with a molar yield of 4.8%. Hsd4A, encoding a β-hydroxyacyl-CoA dehydrogenase, and fadA5, encoding an acyl-CoA thiolase, were separately knocked out to block the C19 pathway in the Δ¹-dehydrogenation-deficient strain. The two engineered strains were able to accumulate 0.59 g L⁻¹ and 0.47 g L⁻¹ 9-OH-4-HP from 1 g L⁻¹ phytosterols, respectively. Furthermore, hsd4A and fadA5 were knocked out simultaneously in the Δ¹-dehydrogenation-deficient strain. The 9-OH-4-HP production from the Hsd4A and FadA5 deficient strain was 11.9% higher than that of the Hsd4A deficient strain and 40.4% higher than that of the strain with FadA5 deficiency strain, respectively. The purity of 9-OH-4-HP obtained from the Hsd4A and FadA5 deficient strain has reached 94.9%. Subsequently, the catalase katE from Mycobacterium neoaurum and an NADH oxidase, nox, from Bacillus subtilis were overexpressed to improve the intracellular environment, leading to a higher 9-OH-4-HP production. Ultimately, 9-OH-4-HP production reached 3.58 g L⁻¹ from 5 g L⁻¹ phytosterols, and the purity of 9-OH-4-HP improved to 97%. The final 9-OH-4-HP production strain showed the best molar yield of 85.5%, compared with the previous reported strain with 30% molar yield of 9-OH-4-HP.

Conclusion

KstD, Hsd4A, and FadA5 are key enzymes for phytosterol side-chain degradation in the C19 pathway. Double deletion of hsd4A and fadA5 contributes to the blockage of the C19 pathway. Improving the intracellular environment of Mycobacterium neoaurum during phytosterol bioconversion could accelerate the conversion process and enhance the productivity of target sterol derivatives.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01717-w.

Coexpression of VHb and MceG genes in Mycobacterium sp. Strain LZ2 enhances androstenone production via immobilized repeated batch fermentation

Androstenone production is limited by low-efficiency substrate transport and dissolved oxygen levels during fermentation. In this study, the coexpression of the optimized Vitreoscilla hemoglobin (VHb) and sterol transporter ATPase (MceG) genes in Mycobacterium sp. LZ2 (Msp) was investigated to alleviate dissolved oxygen and mass transfer limitations. Results revealed that Msp-vgb/mceG effectively improved the growth, production, and adaptation to dissolved oxygen compared with those of Msp. The increased catalase activity and reduced intracellular ROS levels enhanced cell viability and promoted transcription of genes critical for phytosterol metabolism. Bagasse as an immobilization carrier increased the productivity of Msp-vgb/mceG by 56%. Immobilized repeat batch fermentation reduced the biotransformation period from 60 days to 37 days and improved the productivity from 0.039 g/L/h to 0.069 g/L/h. To the best of our knowledge, this work is the first study on the immobilization of recombinant mycobacteria on bagasse for androstenone production.

Mycolicibacterium cell factory for the production of steroid-based drug intermediates

Steroid-based drugs have been developed as the second largest medical category in pharmaceutics. The well-established route of steroid industry includes two steps: the conversion of natural products with a steroid framework to steroid-based drug intermediates and the synthesis of varied steroid-based drugs from steroid-based drug intermediates. The biosynthesis of steroid-based drug intermediates from phytosterols by Mycolicibacterium cell factories bypasses the potential undersupply of diosgenin in the traditional steroid chemical industry. Moreover, the biosynthesis route shows advantages on multiple steroid-based drug intermediate products, more ecofriendly processes, and consecutive reactions carried out in one operation step and in one pot. Androsta-4-ene-3,17-dione (AD), androsta-1,4-diene-3,17-dione (ADD) and 9-hydroxyandrostra-4-ene-3,17-dione (9-OH-AD) are the representative steroid-based drug intermediates synthesized by mycolicibacteria. Other steroid metabolites of mycolicibacteria, like 4-androstene-17β-ol-3-one (TS), 22-hydroxy-23,24-bisnorchol-4-ene-3-one (4-HBC), 22-hydroxy-23,24-bisnorchol-1,4-diene-3-one (1,4-HBC), 9,22-dihydroxy-23,24-bisnorchol-4-ene-3-one (9-OH-HBC), 3aα-H-4α-(3'-propionic acid)-7aβ-methylhexahydro-1,5-indanedione (HIP) and 3aα-H-4α-(3'-propionic acid)-5α-hydroxy-7aβ-methylhexahydro-1-indanone-δ-lactone (HIL), also show values as steroid-based drug intermediates. To improve the bio-production efficiency of the steroid-based drug intermediates, mycolicibacterial strains and biotransformation processes have been continuously studied in the past decades. Many mycolicibacteria that accumulate steroid drug intermediates have been isolated, and subsequently optimized by conventional mutagenesis and genetic engineering. Especially, with the clarification of the mycolicibacterial steroid metabolic pathway and the developments on gene editing technologies, rational design is becoming an important measure for the construction and optimization of engineered mycolicibacteria strains that produce steroid-based drug intermediates. Hence, by reviewing researches in the past two decades, this article updates the overall process of steroid metabolism in mycolicibacteria and provides comprehensive schemes for the rational construction of mycolicibacterial strains that accumulate steroid-based drug intermediates. In addition, the special strategies for the bioconversion of highly hydrophobic steroid in aqueous media are discussed as well.

Insights into chronic zinc oxide nanoparticle stress responses of biological nitrogen removal system with nitrous oxide emission and its recovery potential

The nitrogen transformation performances and greenhouse gas nitrous oxide (N₂O) emissions in a sequencing batch reactor under chronic exposure to zinc oxide nanoparticles (ZnO NPs) were quantified and the system's self-recovery potentials were assessed. ZnO NPs posed a dose-dependent depression effect on the removal efficiencies of ammonia nitrogen (NH₄⁺-N) and total nitrogen (TN), and the N₂O emissions. The suppressed N₂O emissions had a positive relationship with the activity ratios of nitrite/NO reductases and N₂O reductase, and were expected to be caused by the inhibited heterotrophic denitrification process. The inhibition of glucose metabolism key enzymes and electron transport chain activities would be responsible for the heterotrophic denitrification performances deterioration. Furthermore, the removal efficiencies of NH₄⁺-N and TN were recovered to control levels through the nitrite-shunt. However, the N₂O emission increased significantly above the control during the recovery period mainly due to the irreversibility of the depressed nitrite oxidation activities.

The Inhibitory Effect of Cyclodextrin on Oxygen Bioavailability Is a Key Factor for the Metabolic Flux Redistribution Toward Steroid Alcohols in Phytosterol Resting Cells Bioconversion

In the present work, we tried to identify the mechanism why by which the steroid alcohols accumulated when hydroxypropyl-β-cyclodextrin (HP-β-CD) was present to enhance the sterol conversion rate. Compared with the bioconversion system without HP-β-CD, the reaction rate was greatly improved in presence of HP-β-CD, but the steroid alcohols largely accumulated concurrently. In a reaction system with an enhanced reaction rate, the higher intracellular NADH/NAD⁺ level was detected, and the production of steroid alcohols increased also. Mycobacterium neoaurum mutants with higher KshA activity (3-ketosteroid 9α-hydrolase, a monooxygenase hydroxylating the nucleus at C-9 at the expense of NAD(P)H consumption) reduced the steroid alcohol production, and in the meantime, the NADH/NAD⁺ level was decreased consequently. Further research found that oxygen availability was seriously inhibited by the cyclodextrin in a reaction system. These results indicated that NADH formed in the bioconversion was not properly regenerated via the respiratory chain because of the poor oxygen bioavailability. The inhibitory effect of cyclodextrin on oxygen bioavailability is a key factor for the metabolic flux redistribution toward steroid alcohols in phytosterol resting cells bioconversion.

The potential co-benefits for health, economy and climate by substituting raw coal with waste cooking oil as a winter heating fuel in rural households of northern China

The toxic emissions from coal combustion associated with domestic winter heating requirements are an important public health issue. Waste cooking oil (WCO) holds promise as a means of reducing pollutant emissions thereby improving human health with the co-benefit of decreasing climate-forcing gas emissions by avoiding the combustion of mineral coal. With an annual production of ~2.17 Mt of WCO in Northern China, it could be used to meet the winter heating demand of ~3.25 million rural households, offsetting ~9.83 Mt of raw coal consumption. Through the adoption of coal-to-WCO shift in rural regions of 15 provinces, approximately 15.0%, 15.6%, 15.9% and 13.7%, respectively of CO, PM_2.5, SO₂ and NO_X emissions would be eliminated. It is estimated that such a change would remove the respective contributions of these pollutants to the premature deaths of respectively, 63,400, 29,300, 173,00 and 31,300 rural residents. Such a positive health impact on the labor cohort would reduce the loss of labor supply and work time, as well as producing billions of RMB in economic benefits. WCO-based heating technology has the same effect on the reduction of GWC₁₀₀ value as other modern energy carriers while also being cheaper and sustainable, long term. Reducing household emissions by substituting raw coal with green energy is a vital strategy to support pathways for sustainable environment design. The results of this work for the coal-to-WCO shift can reinforce the support for coal phase-out in China.

Biosynthesis and Industrial Production of Androsteroids

Steroids are a group of organic compounds that include sex hormones, adrenal cortical hormones, sterols, and phytosterols. In mammals, steroid biosynthesis starts from cholesterol via multiple steps to the final steroid and occurs in the gonads, adrenal glands, and placenta. This highly regulated pathway involves several cytochrome P450, as well as different dehydrogenases and reductases. Steroids in mammals have also been associated with drug production. Steroid pharmaceuticals such as testosterone and progesterone represent the second largest category of marketed medical products. There heterologous production through microbial transformation of phytosterols has gained interest in the last couple of decades. Phytosterols being the plants sterols serve as inexpensive substrates for the production of steroid derivatives. Various genes and biochemical pathways involved in phytosterol degradation have been identified in many Rhodococcus and Mycobacterium species. Apart from an early investigation in mammals, presence of steroids such as androsteroids and progesterone has also been demonstrated in plants. Their main role is linked with growth, development, and reproduction. Even though plants share some chemical features with mammals, the biosynthesis is different, with the first C22 hydroxylation as an example. This is performed by CYP11A1 in mammals and CYP90B1 in plants. Moreover, the entire plant steroid biosynthesis is not fully elucidated. Knowing this pathway could provide new processes for the industrial biotechnological production of steroid hormones in plants.

A recycled batch biotransformation strategy for 22-hydroxy-23,24-bisnorchol-4-ene-3-one production from high concentration of phytosterols by mycobacterial resting cells

OBJECTIVES

To realize a practical technology for recycling both cyclodextrin and resting-cells at the same time in phytosterol biotransformation using mycobacterial resting cells.

RESULTS

In order to produce 22-hydroxy-23,24-bisnorchol-4-ene-3-one (HBC) efficiently and low-costly, a recycled phytosterols (PS) biotransformation process using mycobacterial resting cells was developed. By optimizing the ratio of hydroxypropyl-β-cyclodextrin (HP-β-CD) and PS to 1:1 (w/w), most products crystallized during the biotransformation process. So, the HBC was easily separated by low-speed (900×g) centrifugation with yield of 92%. The resting cells, HP-β-CD and the residual products and substrates left in the reaction system were reused for another bioconversion cycle after PS supplement. Three continuous cycles were achieved without the supplement of cells and HP-β-CD. In each batch, 80 g L^-1 of PS was transformed to HBC with the space-time yield of HBC of 8.9-12.8 g L^-1 day^-1.

CONCLUSIONS

This strategy reduced the cost of HBC production and simplified the purification process.

Efficient repeated batch production of androstenedione using untreated cane molasses by Mycobacterium neoaurum driven by ATP futile cycle

The biotransformation of phytosterol to androstenedione (AD) by mycobacteria is a unique process accompanied by energy-producing. However, high intracellular ATP content can severely inhibit the efficient production of AD. In this study, a novel citrate-based ATP futile cycle (AFC) and pyruvate-based AFC were constructed for the first time. Application of AFCs reduced intracellular ATP and propionyl-CoA levels and increased NAD⁺/NADH ratios and cell viability. The forced consumption of ATP promotes the transcription of critical genes in propionyl-CoA metabolism. The synergistic effect of enhanced propionyl-CoA metabolism and AFC increased AD conversion yield from 60.6% to 97.3%. The AD productivity was further improved by repeated batch fermentation using untreated cane molasses. The maximum productivity was 181% higher than that of the original strain. Therefore, the strategy of combining AFC and repeated batch fermentation is a valuable tool for the efficient and low-cost production of AD and other steroidal pharmaceutical precursors.

Overexpression of nicotinamide mononucleotide adenylyltransferase (nmnat) increases the growth rate, Ca2+ concentration and cellulase production in Ganoderma lucidum

Identifying new and economical means to utilize diverse lignocellulosic biomass is an urgent task. Ganoderma lucidum is a well-known edible and medicinal basidiomycete with an excellent ability to degrade a wide range of cellulosic biomass, and its nutrient use efficiency is closely related to the activity of extracellular cellulase. Intracellular nicotinamide adenine dinucleotide (NAD⁺) biosynthesis is controlled in response to nutritional status, and NAD⁺ is an essential metabolite involved in diverse cellular processes. Nicotinamide mononucleotide adenylyltransferase (NMNAT) is a common enzyme in three NAD⁺ synthesis pathways. In this study, a homologous gene of nmnat was cloned from G. lucidum and two G. lucidum overexpression strains, OE::nmnat4 and OE::nmnat19, were constructed using an Agrobacterium tumefaciens-mediated transformation method. The G. lucidum nmnat overexpression strains showed obviously increased colony growth on different carbon sources, and intracellular Ca²⁺ concentrations in the G. lucidum OE::nmnat4 and OE::nmnat19 strains were increased by 2.04- and 2.30-fold, respectively, compared with those in the wild-type (WT) strains. In the G. lucidum OE::nmnat4 and OE::nmnat19 strains, endo-β-glucanase (CMCase) activity increased by approximately 2.8- and 3-fold, while β-glucosidase (pNPGase) activity increased by approximately 1.9- and 2.1-fold, respectively, compared with the activity in the WT strains. Furthermore, overexpression of NAD⁺ synthesis pathways was found to elicit cellulase production by increasing the intracellular Ca²⁺ concentration. In summary, this study is the first to demonstrate that increased intracellular NAD⁺ contents through overexpression of the nmnat gene of NAD⁺ synthesis pathways may increase cellulase production by increasing intracellular Ca²⁺ concentrations in G. lucidum. KEY POINTS: • The concentration of NAD⁺influences cellulase production in G. lucidum. • The concentration of NAD⁺influences the intracellular Ca²⁺concentration in G. lucidum. • The concentration of NAD⁺influences cellulase production by eliciting a change in intracellular Ca²⁺in G. lucidum.

Biotransformation of Phytosterols to Androst-1,4-Diene-3,17-Dione by Mycobacterium sp. ZFZ Expressing 3-Ketosteroid-Δ1-Dehydrogenase

As an important hormone drug intermediate, androst-1,4-diene-3,17-dione can be bio-converted from phytosterols. However, separation and purification in the downstream process are very difficult due to the similarity in structure and physiological characteristics between ADD and androstenedione (AD). This phenomenon was correlated to the insufficient enzyme activity of 3-ketosteroid-Δ1-dehydrogenase (KSDD), which specifically catalyzes the C1,2 dehydrogenation of AD. In order to obtain a highly purified ADD from phytosterols, the dehydrogenation effect of different kinds of KSDDs and the transcription effect of four promoter sequences on ksdd were analyzed in Mycobacterium sp. ZFZ (ZFZ), the cell host that transform phytosterols to AD in the oil-aqueous system. A tandem KSDD expression cassette containing strain ZFZ-2111 yielded 2.06 ± 0.09 g L−1 ADD, with a molar ratio of ADD/AD at 41.47:1.00 in 120 h. In waste cooking oil-aqueous media, the proportion of ADD in the fermentation by ZFZ-2111 was 92%. The present study provides a reliable theoretical basis for the step-by-step transformation of phytosterols to ADD.

Ferulic Acid Ameliorates MPP+/MPTP-Induced Oxidative Stress via ERK1/2-Dependent Nrf2 Activation: Translational Implications for Parkinson Disease Treatment

Parkinson's disease (PD) is a neurodegenerative disorder closely associated with oxidative stress. The biochemical and cellular alterations that occur after cell and mouse treatment with the parkinsonism-inducing neurotoxin MPP⁺/MPTP are remarkably similar to those observed in idiopathic PD. Previously, we showed that ferulic acid (FA) has antioxidant properties and the ability to activate nuclear factor E2-related factor 2 (Nrf2). The present study tested the hypothesis that FA attenuates MPP⁺/MPTP-induced oxidative stress by regulating crosstalk between sirtuin 2 (SIRT2) and Nrf2 pathways. To test this hypothesis, we performed in vitro and in vivo studies using MPP⁺/MPTP-challenged SH-SY5Y cells or mice treated with or not with FA. FA marginally inhibited SIRT2 in parallel with α-synuclein at levels of transcription and translation in SH-SY5Y cells challenged with MPP⁺. Moreover, FA attenuated MPP⁺-induced oxidative stress, as indicated by reactive oxygen species, lipid hydroperoxides, GSH/GSSG ratio, and NAD⁺/NADH ratio. Mechanistically, FA strongly upregulated the glutamate cysteine ligase catalytic subunit and heme oxygenase-1 expression at the levels of transcription and translation. Interestingly, FA-mediated extracellular signal-regulated kinases 1 and 2 (ERK1/2) activation contributed to nuclear accumulation of Nrf2 via de novo synthesis, which was validated by the use of dominant negative ERK2. Surprisingly, activation of the ERK1/2 and inhibition of SIRT2 by FA are mediated by independent mechanisms. Furthermore, FA ameliorated motor deficits and oxidative stress in the ventral midbrain in MPTP-treated (25 mg/kg, i.p., daily for 5 days) wild-type mice and α-synuclein knockout mice, but not in Nrf2 knockout mice. Collectively, FA exerts antioxidant effects through ERK1/2-mediated activation of the Nrf2 pathway, and these results may have important translational value for the treatment of PD.

Improving phytosterol biotransformation at low nitrogen levels by enhancing the methylcitrate cycle with transcriptional regulators PrpR and GlnR of Mycobacterium neoaurum

BACKGROUND

Androstenedione (AD) is an important steroid medicine intermediate that is obtained via the degradation of phytosterols by mycobacteria. The production process of AD is mainly the degradation of the phytosterol aliphatic side chain, which is accompanied by the production of propionyl CoA. Excessive accumulation of intracellular propionyl-CoA produces a toxic effect in mycobacteria, which restricts the improvement of production efficiency. The 2-methylcitrate cycle pathway (MCC) plays a significant role in the detoxification of propionyl-CoA in bacterial. The effect of the MCC on phytosterol biotransformation in mycobacteria has not been elucidated in detail. Meanwhile, reducing fermentation cost has always been an important issue to be solved in the optimizing of the bioprocess.

RESULTS

There is a complete MCC in Mycobacterium neoaurum (MNR), prpC, prpD and prpB in the prp operon encode methylcitrate synthase, methylcitrate dehydratase and methylisocitrate lyase involved in MCC, and PrpR is a specific transcriptional activator of prp operon. After the overexpression of prpDCB and prpR in MNR, the significantly improved transcription levels of prpC, prpD and prpB were observed. The highest conversion ratios of AD obtained by MNR-prpDBC and MNR-prpR increased from 72.3 ± 2.5% to 82.2 ± 2.2% and 90.6 ± 2.6%, respectively. Through enhanced the PrpR of MNR, the in intracellular propionyl-CoA levels decreased by 43 ± 3%, and the cell viability improved by 22 ± 1% compared to MNR at 96 h. The nitrogen transcription regulator GlnR repressed prp operon transcription in a nitrogen-limited medium. The glnR deletion enhanced the transcription level of prpDBC and the biotransformation ability of MNR. MNR-prpR/ΔglnR was constructed by the overexpression of prpR in the glnR-deleted strain showed adaptability to low nitrogen. The highest AD conversion ratio by MNR-prpR/ΔglnR was 92.8 ± 2.7% at low nitrogen level, which was 1.4 times higher than that of MNR.

CONCLUSION

Improvement in phytosterol biotransformation after the enhancement of propionyl-CoA metabolism through the combined modifications of the prp operon and glnR of mycobacteria was investigated for the first time. The overexpress of prpR in MNR can increase the transcription of essential genes (prpC, prpD and prpB) of MCC, reduce the intracellular propionyl-CoA level and improve bacterial viability. The knockout of glnR can enhance the adaptability of MNR to the nitrogen source. In the MNRΔglnR strain, overexpress of prpR can achieve efficient production of AD at low nitrogen levels, thus reducing the production cost. This strategy provides a reference for the economic and effective production of other valuable steroid metabolites from phytosterol in the pharmaceutical industry.

Economical production of androstenedione and 9α-hydroxyandrostenedione using untreated cane molasses by recombinant mycobacteria

Production of androstenedione (AD) and 9α-hydroxyandrostenedione (9α-OH-AD) by recombinant mycobacteria using untreated cane molasses and hydrolysate of mycobacterial cells (HMC) was investigated for the first time. B-vitamins feeding experiment and reverse transcription-PCR analysis showed that propionyl-CoA carboxylase (PCC) plays an important role in the phytosterol biotransformation of mycobacteria. The respective AD and 9α-OH-AD conversion ratios were increased by 2.91 and 1.48 times through coexpression of PCC and NADH dehydrogenase. The highest conversion ratios of AD and 9α-OH-AD obtained by using a co-feeding strategy of cane molasses and HMC reached 96.38% and 95.04%, respectively, and the total costs of carbon and nitrogen sources for the culture medium were reduced by 29.89% and 49.49%, respectively. Taking the results together, untreated cane molasses and HMC can be used for the economical production of steroidal pharmaceutical precursors by mycobacteria. This study offers an economical and green strategy for steroidal pharmaceutical precursor production.