Microbial Conversion of α-Ionone, α-Methylionone, and α-Isomethylionone

α-Ionone, α-methylionone, and α-isomethylionone were converted by Aspergillus niger JTS 191. The individual bioconversion products from α-ionone were isolated and identified by spectrometry and organic synthesis. The major products were cis-3-hydroxy-α-ionone, trans-3-hydroxy-α-ionone, and 3-oxo-α-ionone. 2,3-Dehydro-α-ionone, 3,4-dehydro-β-ionone, and 1-(6,6-dimethyl-2-methylene-3-cyclohexenyl)-buten-3-one were also identified. Analogous bioconversion products from α-methylionone and α-isomethylionone were also identified. From results of gas-liquid chromatographic analysis during the fermentation, we propose a metabolic pathway for α-ionones and elucidation of stereochemical features of the bioconversion.     

Biotransformation of geraniol, nerol and citral by sporulated surface cultures of Aspergillus niger and Penicillium sp

The biotransformation of geraniol, nerol and citral by Aspergillus niger was studied. A comparison was made between submerged liquid, sporulated surface cultures and spore suspensions. This bioconversion was also carried out with surface cultures of Penicillium sp. The main bioconversion products obtained from geraniol and nerol by liquid cultures of A. niger were linalool and alpha-terpineol. Linalool, alpha-terpineol and limonene were the main products obtained from nerol and citral by sporulated surface cultures, whereas geraniol was converted predominantly to linalool, also resulting in higher yields. Bioconversion of nerol with Penicillium chrysogenum yielded mainly alpha-terpineol and some unidentified compounds. With P. rugulosum the major bioconversion product from nerol and citral was linalool. The bioconversion of nerol to alpha-terpineol and linalool by spore suspensions of A. niger was also investigated. Finally the biotransformation with sporulated surface cultures was also monitored by solid phase microextraction (SPME). It was found that SPME is a very fast and efficient screening technique for biotransformation experiments.     

Studies on Bacillus stearothermophilus. Part IV. Influence of enhancers on biotransformation of testosterone

The impact of chemical enhancers on the biotransformation of testosterone has been exploited. Application of crude cell concentrates to produce Bacillus stearothermophilus-mediated bioconversion of testosterone at 65 degrees C for 72 h has been examined. After incubation, the xenobiotic substrate was added to the concentrated whole cell suspensions. The enhancer molecules were included in the whole cell suspension. The resultant products, after extraction into an organic solvent, were purified by thin layer chromatography and identification was carried out through spectroscopic data. Five steroid metabolites 9,10-seco-4-androstene-3,9,17-trione, 5alpha-androstan-3,6,17-trione, 17beta-hydroxy-5alpha-androstan-3,6-dione, 3beta,17beta-dihydroxyandrost-4-ene-6-one and 17beta-hydroxyandrost-4,6-diene-3-one were identified as biotransformation products of testosterone. A possible biosynthetic route for these bioconversion products is postulated.     

Challenges and pitfalls of P450-dependent (+)-valencene bioconversion by Saccharomyces cerevisiae

Natural nootkatone is a high value ingredient for the flavor and fragrance industry because of its grapefruit flavor/odor, low sensorial threshold and low availability. Valencene conversion into nootkatol and nootkatone is known to be catalyzed by cytochrome P450 enzymes from both prokaryotic and eukaryotic organisms, but so far development of a viable bioconversion process using either native microorganisms or recombinant enzymes was not successful. Using an in silico gene-mining approach, we selected 4 potential candidate P450 enzymes from higher plants and identified two of them that selectively converted (+)-valencene into β-nootkatol with high efficiency when tested using recombinant yeast microsomes in vitro. Recombinant yeast expressing CYP71D51v2 from tobacco and a P450 reductase from arabidopsis was used for optimization of a bioconversion process. Bioconversion assays led to production of β-nootkatol and nootkatone, but with low yields that decreased upon increase of the substrate concentration. The reasons for this low bioconversion efficiency were further investigated and several factors potentially hampering industry-compatible valencene bioconversion were identified. One is the toxicity of the products for yeast at concentrations exceeding 100 mg L⁻¹. The second is the accumulation of β-nootkatol in yeast endomembranes. The third is the inhibition of the CYP71D51v2 hydroxylation reaction by the products. Furthermore, we observed that the formation of nootkatone from β-nootkatol is not P450-dependent but catalyzed by a yeast component. Based on these data, we propose new strategies for implementation of a viable P450-based bioconversion process.     

Biotransformation of limonene by Pseudomonas putida

From a study of three fungal and 15 bacterial strains, it was observed that Pseudomonas putida MTCC 1072 oxidized limonene with the highest efficiency of. Fermentation of limonene by P. putida MTCC 1072 was conducted for 120 h at 30 degrees C at a fixed pH of 5.0. Major bioconversion products were isolated and characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopy, and by elemental analysis. The bioconversion products were identified as perillyl alcohol and p-menth-1-ene-6,8-diol, and under optimum conditions the yields were 36% and 44%, respectively (a rate kinetic model indicated corresponding limiting yields of 44% and 56%). No further degradation of the products was observed using this bacteria.     

Comparative study on the action of S-(+)-carvone, in situ, on the potato storage fungi Fusarium solani var. coeruleum and F. sulphureum

Growth of Fusarium sulphureum was inhibited by S-(+)-carvone administered via the gas phase. Under the same conditions, the related fungus F. solani var. coeruleum was not inhibited. In liquid medium, both fungi were found to convert S-(+)-carvone with the same rate, mainly into isodihydrocarvone, isodihydrocarveol and neoisodihydrocarveol. Only a slight difference in the relative amounts of the bioconversion products was observed. Since the bioconversion products did not inhibit the growth of the fungi to the same extent as S-(+)-carvone, the process can be considered as a detoxification mechanism. The bioconversion as such cannot account for the observed difference in growth inhibition.     

Biotransformation of lignin: Mechanisms,applications and future work

As one of the most abundant polymers in biosphere, lignin has attracted extensive attention as a kind of promising feedstock for biofuel and bio-based products. However, the utilization of lignin presents various challenges in that its complex composition and structure and high resistance to degradation. Lignin conversion through biological platform harnesses the catalytic power of microorganisms to decompose complex lignin molecules and obtain value-added products through biosynthesis. Given the heterogeneity of lignin, various microbial metabolic pathways are involved in lignin bioconversion processes, which has been characterized in extensive research work. With different types of lignin substrates (e.g., model compounds, technical lignin, and lignocellulosic biomass), several bacterial and fungal species have been proved to own lignin-degrading abilities and accumulate microbial products (e.g., lipid and polyhydroxyalkanoates), while the lignin conversion efficiencies are still relatively low. Genetic and metabolic strategies have been developed to enhance lignin biodegradation by reprogramming microbial metabolism, and diverse products, such as vanillin and dicarboxylic acids were also produced from lignin. This article aims at presenting a comprehensive review on lignin bioconversion including lignin degradation mechanisms, metabolic pathways, and applications for the production of value-added bioproducts. Advanced techniques on genetic and metabolic engineering are also covered in the recent development of biological platforms for lignin utilization. To conclude this article, the existing challenges for efficient lignin bioprocessing are analyzed and possible directions for future work are proposed.     

Biotransformation of tabersonine in cell suspension cultures of Catharanthus roseus.

To investigate the reactions involved in the biosynthesis of vindoline from tabersonine, the bioconversion products formed when the latter compound was fed to cell suspension cultures of Catharanthus roseus were isolated and characterized. Two biotransformation products of tabersonine were isolated and shown to be lochnericine, which is formed by epoxidation of tabersonine at positions 14, 15, and lochnerinine, the 11-methoxylation product of lochnericine. The bioconversion ratio of the main biotransformation product, lochnericine, reached a value of 80.6% within three days.     

Directed evolution of toluene dioxygenase from Pseudomonas putida for improved selectivity toward cis-indandiol during indene bioconversion

Toluene dioxygenase (TDO) from Pseudomonas putida F1 converts indene to a mixture of cis-indandiol (racemic), 1-indenol, and 1-indanone. The desired product, cis-(1S,2R)-indandiol, is a potential key intermediate in the chemical synthesis of indinavir sulfate (Crixivan), Merck's HIV-1 protease inhibitor for the treatment of AIDS. To reduce the undesirable byproducts 1-indenol and 1-indanone formed during indene bioconversion, the recombinant TDO expressed in Escherichia coli was evolved by directed evolution using the error-prone polymerase chain reaction (epPCR) method. High-throughput fluorometric and spectrophotometric assays were developed for rapid screening of the mutant libraries in a 96-well format. Mutants with reduced 1-indenol by-product formation were identified, and the individual indene bioconversion product profiles of the selected mutants were confirmed by HPLC. Changes in the amino acid sequence of the mutant enzymes were identified by analyzing the nucleotide sequence of the genes. A mutant with the most desirable product profile from each library, defined as the most reduced 1-indenol concentration and with the highest cis-(1S,2R)-indandiol enantiomeric excess, was used to perform each subsequent round of mutagenesis. After three rounds of mutagenesis and screening, mutant 1C4-3G was identified to have a threefold reduction in 1-indenol formation over the wild type (20% vs 60% of total products) and a 40% increase of product (cis-indandiol) yield.     

Microbiological transformation of mycophenolic acid

In our microbial screening program, we have isolated a fungal strain which produced mycophenolic acid (MPA). This compound is a selective inhibitor of guanine synthesis and, therefore, it has antibacterial, antiviral, antitumor and selective immunosuppressive activities, too. This last effect was utilised by Roche-Syntex to develop a derivative of MPA to the immunosuppressive drug CellCept®.

In order to obtain novel derivatives of MPA with an enhanced activity, we applied bioconversion of MPA with various microorganisms. TLC with densitometric evaluation and HPLC methods were developed for measurement of MPA derivatives. In the course of the bioconversion of MPA by using various types of microorganisms amidation of the carboxyl group, hydroxylation of the C₄-methyl group and formation of glycoside derivatives from the hydroxyl group located on C₇ were observed as the most frequently occurring transformations. The structures of bioconversion products were determined by UV, IR, ¹H NMR, ¹³C NMR and mass spectroscopic methods.

The taxonomic features of cultures of the species applied in the bioconversion were also determined.     

Δ′-Dehydrogenation of steroids byArthrobacter simplex immobilized in calcium polygalacturonate beads

Summary Arthrobacter simplex ATCC 6946 (viable cells) was immobilized in a calcium polygalacturonate gel. The trapped cells were used for repeated batchwise bioconversion of steroids. Reichstein's compound S and hydrocortisone were dehydrogenated introducing a double bond between C₁ and C₂ of ring A. The products 1-dehydro S and prednisolone, respectively, were identified by high pressure liquid chromatography. Steroid dehydrogenase activity increased in the system when an artificial electron acceptor, such as menadione (vitamin K₃) was present in the reaction mixture. An airlift-type reactor was used to bioconvert up to 90% of substrate in 15 min, under optimal conditions. The gel entrapped cell preparations were used for repeated batch bioconversion during 30 days; 69 batch bioconversions for Reichstein's compound S were performed during 15 days of operation of the reactor. The operational stability of the process and the feasibility of repeated batch bioconversions was shown to be comparable to similar processes.     

Biocatalytic and semisynthetic optimization of the anti-invasive tobacco (1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol

Tobacco cembranoids were reported to inhibit tumorigenesis. Biocatalysis of (1S,2E,4R,6R,7E,11E)-2,7,11-cembratriene-4,6-diol (1) using the symbiotic Bacillus sp. NC5, Bacillus sp. NK8, and Bacillus sp. NK7, isolated from the Red Sea sponge Negombata magnifica, afforded two new and four known hydroxylated metabolites 3-8. The use of symbiotic marine bacteria as biocatalysts for bioactive natural product scaffolds is very rare. Cembranoid 1 carbamate analogs 9-11 were prepared by its reaction with corresponding isocyanates. Cembranoid 1 and its bioconversion and carabamate products show anti-invasive activity against the human highly metastatic prostate PC-3M cancer cell line at 10-50 nM doses in Matrigel assay.     

Novel bioconversion products of andrographolide by Aspergillus ochraceus and their cytotoxic activities against human tumor cell lines

Andrographolide (1), a major labdane diterpenoidal constituent of a famous traditional Chinese of Andrographis paniculata, exhibits a wide spectrum of biological activities including antibacterial, anti-inflammatory, and antitumor properties. Bioconversion of andrographolide (1) by Aspergillus ochraceus (ATCC 1008) was investigated. Five bioconversion products were isolated and identified. Their structures were identified to be 8β-hydroxy-8(17)-dihydroandrographolide (2), 8β-hydroxy-8(17)-dihydro-14-deoxy-11,12-didehydroandrographolide (3), 8β-hydroxy-8(17)-dihydro-14-deoxy-11,12-didehydroandrographolide 19-oic acid (4), 14-deoxy-11,12-didehydroandrographolide (5), and 14-deoxy-11,12-didehydroandrographolide 19-oic acid (6). Metabolites 2–4 were novel compounds. The proposed biosynthetic pathways of andrographolide by A. ochraceus were drawn. Most bioconversion products showed potential cytotoxic activities against human breast cancer (MCF-7), human colon cancer (HCT-116) and leukemia (HL-60) cell lines.     

Bioconversion of arachidonic acid in the human gastrointestinal tract

The data presented demonstrate that the bioconversion of [14C]arachidonic acid in homogenates like these is very easily influenced by protein (enzyme) and substrate concentration as well as exogenous cofactors. This is not unexpected but variations will lead to artifactual differences. Neither quantitative nor qualitative differences could be detected between biopsies taken from healthy as compared to diseased individuals. No products other than PGE2, PGF2 alpha, TxB2, and 6-keto-PGF1 alpha (and metabolites thereof) could be demonstrated although special efforts were undertaken to determine whether there was any detectable lipoxygenase activity. Therefore it seems that future studies on the possible roles of prostaglandins in gastrointestinal physiology should be restricted to those compounds identified, primarily PGE2 and PGF2 alpha. The monotony in the pattern of products formed in homogenates from different tissues also suggests that in order to be able to detect possible differences between various conditions such studies should involve a minimum of tissue manipulation.     

Further kinetic characterization of alginate-entrapped cells of Mucuna pruriens L

Alginate-entrapped cells of Mucuna pruriens L. hydroxylate L -tyrosine, tyramine, para-hydroxyphenylpropionic acid, and para-hydroxyphenylacetic acid to their corresponding catechols, which were released into the incubation medium. Michaëlis-Menten kinetics was applied for each bioconversion. The apparent affinity constants were comparable with the affinity constants obtained with a homogenate directly prepared from the cells used for entrapment and with a derived partly purified phenoloxidase. The values found for the apparent maximum rates of bioconversion of the entrapped cells were ca. 50% of the values of the maximum rates of bioconversion of the cell homogenate, indicating that the entrapped cell system was not operating optimally. The effective diffusivities of the substrates and products were measured with alginate-entrapped, inactivated cells. From the five inactivation methods tested, glutaric aldehyde treatment was chosen as the general procedure. Calculated effective diffusivities for the monophenols and catechols demonstrated that these compounds could diffuse freely into and out of the beads. For each bioconversion, the observable modulus was calculated from the initial rate of bioconversion and the effective diffusivity of the substrate. The resulting values indicated that the diffusional supply rate of the substrates was not the limiting factor, except for the conversion of tyramine for which a modulus higher than one was obtained. Analogously, the observable moduli were calculated for oxygen, which was utilized for bioconversion and cell respiration, and these values pointed towards strong oxygen limitation in all cases. The bioconversion rates of the entrapped cells increased with decreasing cell aggregate size. Therefore, it was concluded that direct cell-matrix contact determined the amount of phenoloxidase involved in the bioconversions. The bioconversion rate on a protein basis was constant with enhancement of the bead charge and thus, in spite of limitations, the mixing conditions as such were relatively optimal. In conclusion, the nonoptimal efficiency of the plant cell system studied was caused by oxygen limitation and a partial phenoloxidase participation, but not by mass transfer limitations for substrates and products with the exception of the conversion of tyramine into dopamine.     

Microbial side-chain degradation of ergosterol and its 3-substituted derivatives: A new route for obtaining of deltanoids

The strain of Mycobacterium sp. VKM Ac-1815D was found to convert ergosterol and its 3-acetate mainly to androst-4-ene-3,17-dione (AD) thus demonstrating ability to reduce 7(8)-double bond and hydrolyze sterol ester in addition to oxidation of 3β-hydroxy group, Δ⁵-Δ⁴ isomerization and side-chain degradation. Ergosterol bioconversion in the presence of isoflavones and ions of some bivalent metals - known inhibitors of 3β-hydroxysteroid dehydrogenase, did not alter products composition. Protection of ergosterol 3β-hydroxyl with methoxymethyl group allowed the formation of bioconversion products retaining the Δ^5,7-configuration. The major product was identified by mass-spectrometry and proton NMR as 3-methoxymethoxy-androsta-5,7-diene-17-one (MA). The MA producing activity was found to be inducible with sterols, cholestenone or lithocholic acid, but not with dehydroepiandrosterone, AD, androsta-1,4-ene-3,17-dione or organic acids. Under the optimized conditions, the yield of MA reached 5 g/l from 10 g/l O-methoxymethyl-ergosterol (approx. 60% molar conversion) for 120 h. The results might be applied at the production of novel vitamin D derivatives.     

Cytotoxic biotransformed products from cinobufagin by Mucor spinosus and Aspergillus Niger

Cinobufagin (1) was one of important cardenolidal steroids and major components of Chan'Su, a famous traditional Chinese medicine. Bioconversion of cinobufagin by the fungi of Mucor spinosus and Aspergillus niger were investigated. Nine bioconversion products were obtained from M. spinosus and seven products from A. niger. Their structures were elucidated by high-resolution fast atom bombardment mass spectroscopy (HR-FAB-MS), extensive NMR techniques, including (1)H NMR, (13)C NMR, DEPT, (1)H-(1)H correlation spectroscopy (COSY), two-dimensional nuclear Overhauser effect correlation spectroscopy (NOESY), heteronuclear multiple quantum coherence (HMQC) and heteronuclear multiple bond coherence (HMBC). The in vitro cytotoxic activities against human hepatoma cells (HepG2, SMMC-7221 and BEL-7402) and human leukemia cells (K562, HL-60 and HEL) of all bioconversion products were determined by the MTT method, and their structure-activity relationships (SAR) were discussed.     

Hydroxylation of steroids with nonpolar side chains with 11 alpha-hydroxylase of Rhizopus nigricans

Steroids with nonpolar side chains with 2, 4 and 8 C atoms were used as substrates for the 11 alpha-hydroxylase of Rhizopus nigricans. Their bioconversion was compared to that of progesterone, which was found to be far the best substrate giving the highest total bioconversion. 3-keto-4-ene steroids with nonpolar side chains were converted to their hydroxylated products in a small yield or not at all. The absence of an oxygen function in the side chain did not affect the regio-specificity of the hydroxylation, but resulted in a much lower total bioconversion. The strong effect of the oxygen function and of the length of the side chain on hydroxylation with the 11 alpha-hydroxylase of Rhizopus nigricans was demonstrated.     

Bioconversion of lignocellulosic biomass: biochemical and molecular perspectives

In view of rising prices of crude oil due to increasing fuel demands, the need for alternative sources of bioenergy is expected to increase sharply in the coming years. Among potential alternative bioenergy resources, lignocellulosics have been identified as the prime source of biofuels and other value-added products. Lignocelluloses as agricultural, industrial and forest residuals account for the majority of the total biomass present in the world. To initiate the production of industrially important products from cellulosic biomass, bioconversion of the cellulosic components into fermentable sugars is necessary. A variety of microorganisms including bacteria and fungi may have the ability to degrade the cellulosic biomass to glucose monomers. Bacterial cellulases exist as discrete multi-enzyme complexes, called cellulosomes that consist of multiple subunits. Cellulolytic enzyme systems from the filamentous fungi, especially Trichoderma reesei, contain two exoglucanases or cellobiohydrolases (CBH1 and CBH2), at least four endoglucanases (EG1, EG2, EG3, EG5), and one β-glucosidase. These enzymes act synergistically to catalyse the hydrolysis of cellulose. Different physical parameters such as pH, temperature, adsorption, chemical factors like nitrogen, phosphorus, presence of phenolic compounds and other inhibitors can critically influence the bioconversion of lignocellulose. The production of cellulases by microbial cells is governed by genetic and biochemical controls including induction, catabolite repression, or end product inhibition. Several efforts have been made to increase the production of cellulases through strain improvement by mutagenesis. Various physical and chemical methods have been used to develop bacterial and fungal strains producing higher amounts of cellulase, all with limited success. Cellulosic bioconversion is a complex process and requires the synergistic action of the three enzymatic components consisting of endoglucanases, exoglucanases and β-glucosidases. The co-cultivation of microbes in fermentation can increase the quantity of the desirable components of the cellulase complex. An understanding of the molecular mechanism leading to biodegradation of lignocelluloses and the development of the bioprocessing potential of cellulolytic microorganisms might effectively be accomplished with recombinant DNA technology. For instance, cloning and sequencing of the various cellulolytic genes could economize the cellulase production process. Apart from that, metabolic engineering and genomics approaches have great potential for enhancing our understanding of the molecular mechanism of bioconversion of lignocelluloses to value added economically significant products in the future. JIMB 2008: BioEnergy - Special issue.     

Identification of human,rat and mouse hydrolyzing enzymes bioconverting amino acid ester prodrug of ketoprofen

Alkyl ester prodrugs are well known to be bioconverted by carboxylesterases, particularly in rodents’ by first-pass metabolism in the systemic circulation and liver. However, the bioconversion of structurally more complex esters with polar functional groups is less well understood, especially in humans. Therefore, it is not clear if ester prodrugs can be utilized for targeted drug delivery. In the present study a brain-targeted ester prodrug (1) of ketoprofen, utilizing the l-type amino acid transporter 1 (LAT1) was prepared and the enzymes involved in its metabolism in human plasma and liver S9 subcellular fraction as well as rat brain S9 fraction were identified. Furthermore, species differences among mouse, rat and human plasma and liver S9 fraction were compared. The results showed that bioconversion of the ester prodrug was much faster in mouse plasma compared to human, while it’s half-life in rat plasma was closer to the one of human. Moreover, both rodent species showed more efficient bioconversion in the liver S9 fractions compared to human and relatively efficient bioconversion in the brain S9 fractions. More specifically, butyrylcholinesterase (BChE) and paraoxygenase 1 (PON1) were the main hydrolyzing enzymes of the prodrug 1 in human plasma, while carboxylesterases 1 and 2 (CES1 and CES2) as well as PONs were the main bioconverting enzymes in human liver S9 fractions. In rat brain S9 fraction, acetylcholinesterase (AChE) was hydrolyzing the prodrug 1, although also other unidentified metal-and pH-dependent enzyme(s) were recognized to be participating to the total bioconversion of the compound 1 in the brain.