Bioproduction of lauryl lactone and 4-vinyl guaiacol as value-added chemicals in two-phase biotransformation systems

Spectrophotometric and Fluorimetric High-Throughput Assays for Phenolic Acid Decarboxylase

Biocatalytic decarboxylation of hydroxycinnamic acids yields phenolic styrenes, which are important precursors for antioxidants, epoxy coatings, adhesives and other polymeric materials. Bacillus subtilis decarboxylase (BsPAD) is a cofactor-independent enzyme that catalyzes the cleavage of carbon dioxide from p-coumaric-, caffeic-, and ferulic acid with high catalytic efficiency. Real-time spectroscopic assays for decarboxylase reactions remove the necessity of extensive sample workup, which is required for HPLC, mass spectrometry, gas chromatography, or NMR methods. This work presents two robust and sensitive assays based on photometry and fluorimetry that allow decarboxylation reactions to be followed with high sensitivity while avoiding product extraction and long analysis times. Optimized assay procedures were used to measure BsPAD activity in cell lysates and to determine the kinetic constants (KM and Vmax ) of the purified enzyme for p-coumaric-, caffeic- and ferulic acid. Substrate inhibition was shown for caffeic acid.

Diverting phenylpropanoid pathway flux from sinapine to produce industrially useful 4-vinyl derivatives of hydroxycinnamic acids in Brassicaceous oilseeds

Sinapine (sinapoylcholine) is an antinutritive phenolic compound that can account for up to 2% of seed weight in brassicaceous oilseed crops and reduces the suitability of their protein-rich seed meal for use as animal feed. Sinapine biosynthesis draws on hydroxycinnamic acid precursors produced by the phenylpropanoid pathway. The 4-vinyl derivatives of several hydroxycinnamic acids have industrial applications. For example, 4-vinyl phenol (4-hydroxystyrene) is a building block for a range of synthetic polymers applied in resins, inks, elastomers, and coatings. Here we have expressed a modified bacterial phenolic acid decarboxylase (PAD) in developing seed of Camelina sativa to redirect phenylpropanoid pathway flux from sinapine biosynthesis to the production of 4-vinyl phenols. PAD expression led to a ∼95% reduction in sinapine content in seeds of both glasshouse and field grown C. sativa and to an accumulation of 4-vinyl derivatives of hydroxycinnamic acids, primarily as glycosides. The most prevalent aglycone was 4-vinyl phenol, but 4-vinyl guaiacol, 6-hydroxy-4-vinyl guaiacol and 4-vinylsyringol (Canolol) were also detected. The molar quantity of 4-vinyl phenol glycosides was more than twice that of sinapine in wild type seeds. PAD expression was not associated with an adverse effect on seed yield, harvest index, seed morphology, storage oil content or germination in either glasshouse or field experiments. Our data show that expression of PAD in brassicaceous oilseeds can supress sinapine accumulation, diverting phenylpropanoid pathway flux into 4-vinyl phenol derivatives, thereby also providing a non-petrochemical source of this class of industrial chemicals.

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A phenolic acid decarboxylase was expressed in developing Camelina sativa seeds.

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Production of the antinutritive phenolic compound sinapine was reduced by 95%.

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Hydroxycinnamic acids were converted to 4-vinyl phenols and accumulated as glycosides.

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The quantity of 4-vinyl phenols was more than twice that of sinapine in wild type.

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Seed yield appeared not to be affected in either glasshouse or field experiments.

Enzymes, In Vivo Biocatalysis, and Metabolic Engineering for Enabling a Circular Economy and Sustainability

Since the industrial revolution, the rapid growth and development of global industries have depended largely upon the utilization of coal-derived chemicals, and more recently, the utilization of petroleum-based chemicals. These developments have followed a linear economy model (produce, consume, and dispose). As the world is facing a serious threat from the climate change crisis, a more sustainable solution for manufacturing, i.e., circular economy in which waste from the same or different industries can be used as feedstocks or resources for production offers an attractive industrial/business model. In nature, biological systems, i.e., microorganisms routinely use their enzymes and metabolic pathways to convert organic and inorganic wastes to synthesize biochemicals and energy required for their growth. Therefore, an understanding of how selected enzymes convert biobased feedstocks into special (bio)chemicals serves as an important basis from which to build on for applications in biocatalysis, metabolic engineering, and synthetic biology to enable biobased processes that are greener and cleaner for the environment. This review article highlights the current state of knowledge regarding the enzymatic reactions used in converting biobased wastes (lignocellulosic biomass, sugar, phenolic acid, triglyceride, fatty acid, and glycerol) and greenhouse gases (CO₂ and CH₄) into value-added products and discusses the current progress made in their metabolic engineering. The commercial aspects and life cycle assessment of products from enzymatic and metabolic engineering are also discussed. Continued development in the field of metabolic engineering would offer diversified solutions which are sustainable and renewable for manufacturing valuable chemicals.

Efficient and long-term vanillin production from 4-vinylguaiacol using immobilized whole cells expressing Cso2 protein

Vanillin is a well-known fragrant, flavoring compound. Previously, we established a method of coenzyme-independent vanillin production via an oxygenase from Caulobacter segnis ATCC 21756, called Cso2, that converts 4-vinylguaiacol to vanillin and formaldehyde using oxygen. In this study, we found that reactive oxygen species inhibited the catalytic activity of Cso2, and the addition of catalase increased vanillin production. Since Escherichia coli harbors catalases, we used E. coli cells expressing Cso2 to produce vanillin. Cell immobilization in calcium alginate enabled the long-term use of the E. coli cells for vanillin production. Thus, we demonstrate the possibility of using immobilized E. coli cells for both continuous and repeated batch vanillin production without any coenzymes.

Bioproduction of High-Concentration 4-Vinylguaiacol Using Whole-Cell Catalysis Harboring an Organic Solvent-Tolerant Phenolic Acid Decarboxylase From Bacillus atrophaeus

The compound 4-vinyl guaiacol (4-VG) is highly valued and widely applied in the pharmaceutical, cosmetic, and food industries. The bioproduction of 4-VG from ferulic acid (FA) by non-oxidative decarboxylation using phenolic acid decarboxylases is promising but has been hampered by low conversion yields and final product concentrations due to the toxicities of 4-VG and FA. In the current study, a new phenolic acid decarboxylase (BaPAD) was characterized from Bacillus atrophaeus. The BaPAD possessed excellent catalytic activity and stability in various organic solvents. Whole Escherichia coli cells harboring intracellular BaPAD exhibited greater tolerances to FA and 4-VG than those of free BaPAD. A highly efficient aqueous-organic biphasic system was established using 1-octanol as the optimal organic phase for whole-cell catalysis. In this system, a very high concentration (1580 mM, 237.3 g/L) of 4-VG was achieved in a 2 L working volume bioreactor, and the molar conversion yield and productivity reached 98.9% and 18.3 g/L/h in 13 h, respectively.

Functional Autodisplay of Phenolic Acid Decarboxylase using a GDSL Autotransporter on Escherichia coli for Efficient Catalysis of 4-Hydroxycinnamic Acids to Vinylphenol Derivatives

Bioproduction of vinylphenol derivatives, such as 4-vinylguaiacol (4-VG) and 4-vinylphenol (4-VP), from 4-hydroxycinnamic acids, such as ferulic acid (FA) and p-coumaric acid (pCA), employing whole cells expressing phenolic acid decarboxylases (PAD) as a biocatalyst has attracted much attention in recent years. However, the accumulation of 4-VG or 4-VP in the cell may cause high cytotoxicity to Escherichia coli (E. coli) and consequently cell death during the process. In this study, we firstly report the functional display of a phenolic acid decarboxylase (BLPAD) from Bacillus licheniformis using a GDSL autotransporter from Pseudomonas putida on the cell surface of E. coli. Expression and localization of BLPAD on E. coli were verified by SDS-PAGE and protease accessibility. The PelB signal peptide is more effective in guiding the translocation of BLPAD on the cell surface than the native signal peptide of GDSL, and the cell surface displaying BLPAD activity reached 19.72 U/OD600. The cell surface displaying BLPAD showed good reusability and retained 63% of residual activity after 7 cycles of repeated use. In contrast, the residual activity of the intracellular expressing cells was approximately 11% after 3 cycles of reuse. The molar bioconversion yields of 72.6% and 80.4% were achieved at the concentration of 300 mM of FA and pCA in a biphasic toluene/Na2HPO4–citric acid buffer system, respectively. Its good reusability and efficient catalysis suggested that the cell surface displaying BLPAD can be used as a whole-cell biocatalyst for efficient production of 4-VG and 4-VP.

Toward Upscaled Biocatalytic Preparation of Lactone Building Blocks for Polymer Applications

Although Baeyer–Villiger monooxygenases (BVMOs) have gained attention in recent years, there are few cases of their upscaled application for lactone synthesis. A thermostable cyclohexanone monooxygenase from Thermocrispum municipale (TmCHMO) was applied to the oxidation of 3,3,5-trimethylcyclohexanone using a glucose dehydrogenase (GDH) for cofactor regeneration. The reaction progress was improved by optimizing the biocatalyst loading, with investigation into oxygen limitations. The product concentration and productivity were increased by keeping the substrate concentration below the inhibitory level via continuous substrate feeding (CSF). This substrate feeding strategy was evaluated against two biphasic reactions using either toluene or n-butyl acetate as immiscible organic solvents. A product concentration of 38 g L^–1 and a space-time yield of 1.35 g L^–1 h^–1 were achieved during the gram-scale synthesis of the two regioisomeric lactones by applying the CSF strategy. These improvements contribute to the large-scale application of BVMOs in the synthesis of branched building blocks for polymer applications.

Expression and characterization of a 9-cis-epoxycarotenoid dioxygenase from Serratia sp. ATCC 39006 capable of biotransforming isoeugenol and 4-vinylguaiacol to vanillin

A 9-cis-epoxycarotenoid dioxygenase gene from Serratia sp. ATCC 39,006 (SeNCED) was overexpressed in soluble form in E.coli. SeNCED showed the maximum activity at 30 °C and pH 8.0, and it was stable relatively at range of pH 5-10 and temperature of 20 °C to 30 °C. SeNCED effectively catalyzes the side chain double bond cleavage of isoeugenol and 4-vinylguaiacol to vanillin. The kinetic constant Km values toward isoeugenol and 4-vinylguaiacol were 18.92 mM and 6.31 mM and Vmax values were 50.73 IU/g and 4.77 IU/g, respectively. Moreover, the SeNCED exhibited an excellent organic solvent tolerance and the enzyme activity was substantially improved at presence of 10% of trichloromethane. The produced vanillin was achieved at an around 0.53 g/L (3.47 mM) and 0.33 g/L (2.17 mM) after 8 h reaction at 4 mM of isoeugenol and 4-vinylguaiacol, respectively, using transformed Escherichia coli cells harboring SeNCED in the presence of trichloromethane.

Development of Halogenase Enzymes for Use in Synthesis

Nature has evolved halogenase enzymes to regioselectively halogenate a diverse range of biosynthetic precursors, with the halogens introduced often having a profound effect on the biological activity of the resulting natural products. Synthetic endeavors to create non-natural bioactive small molecules for pharmaceutical and agrochemical applications have also arrived at a similar conclusion: halogens can dramatically improve the properties of organic molecules for selective modulation of biological targets in vivo. Consequently, a high proportion of pharmaceuticals and agrochemicals on the market today possess halogens. Halogenated organic compounds are also common intermediates in synthesis and are particularly valuable in metal-catalyzed cross-coupling reactions. Despite the potential utility of organohalogens, traditional nonenzymatic halogenation chemistry utilizes deleterious reagents and often lacks regiocontrol. Reliable, facile, and cleaner methods for the regioselective halogenation of organic compounds are therefore essential in the development of economical and environmentally friendly industrial processes. A potential avenue toward such methods is the use of halogenase enzymes, responsible for the biosynthesis of halogenated natural products, as biocatalysts. This Review will discuss advances in developing halogenases for biocatalysis, potential untapped sources of such biocatalysts and how further optimization of these enzymes is required to achieve the goal of industrial scale biohalogenation.

Biotechnological production of vanillin using immobilized enzymes

Vanillin is an important and popular plant flavor, but the amount of this compound available from plant sources is very limited. Biotechnological methods have high potential for vanillin production as an alternative to extraction from plant sources. Here, we report a new approach using immobilized enzymes for the production of vanillin. The recently discovered oxygenase Cso2 has coenzyme-independent catalytic activity for the conversion of isoeugenol and 4-vinylguaiacol to vanillin. Immobilization of Cso2 on Sepabeads EC-EA anion-exchange carrier conferred enhanced operational stability enabling repetitive use. This immobilized Cso2 catalyst allowed 6.8mg yield of vanillin from isoeugenol through ten reaction cycles at a 1mL scale. The coenzyme-independent decarboxylase Fdc, which has catalytic activity for the conversion of ferulic acid to 4-vinylguaiacol, was also immobilized on Sepabeads EC-EA. We demonstrated that the immobilized Fdc and Cso2 enabled the cascade synthesis of vanillin from ferulic acid via 4-vinylguaiacol with repetitive use of the catalysts. This study is the first example of biotechnological production of vanillin using immobilized enzymes, a process that provides new possibilities for vanillin production.

Prevalence and specificity of Baeyer-Villiger monooxygenases in fungi

Out of 107 fungal strains belonging to three phyla (Ascomycota, Basidiomycota and Zygomycota) and 46 genera, 86 exhibited Baeyer-Villiger monooxygenase (BVMO) activity against racemic bicyclo[3.2.0]heptenone. The strains were classified into three "profiles" based on regio- and enantioselectivity. Statistical analyses of our results, extended by literature data, showed that these profiles could be related to the taxonomic classification of the strains, and suggest that the BVMOs from the Zygomycota phylum may be different in their primary structures from established ones.

High-yield production of vanillin from ferulic acid by a coenzyme-independent decarboxylase/oxygenase two-stage process

Vanillin is one of the world's most important flavor and fragrance compounds in foods and cosmetics. Recently, we demonstrated that vanillin could be produced from ferulic acid via 4-vinylguaiacol in a coenzyme-independent manner using the decarboxylase Fdc and the oxygenase Cso2. In this study, we investigated a new two-pot bioprocess for vanillin production using the whole-cell catalyst of Escherichia coli expressing Fdc in the first stage and that of E. coli expressing Cso2 in the second stage. We first optimized the second-step Cso2 reaction from 4-vinylguaiacol to vanillin, a rate-determining step for the production of vanillin. Addition of FeCl2 to the cultivation medium enhanced the activity of the resulting E. coli cells expressing Cso2, an iron protein belonging to the carotenoid cleavage oxygenase family. Furthermore, a butyl acetate-water biphasic system was effective in improving the production of vanillin. Under the optimized conditions, we attempted to produce vanillin from ferulic acid by a two-pot bioprocess on a flask scale. In the first stage, E. coli cells expressing Fdc rapidly decarboxylated ferulic acid and completely converted 75 mM of this substrate to 4-vinylguaiacol within 2 h at pH 9.0. After the first-stage reaction, cells were removed from the reaction mixture by centrifugation, and the pH of the resulting supernatant was adjusted to 10.5, the optimal pH for Cso2. This solution was subjected to the second-stage reaction. In the second stage, E. coli cells expressing Cso2 efficiently oxidized 4-vinylguaiacol to vanillin. The concentration of vanillin reached 52 mM (7.8 g L(-1)) in 24 h, which is the highest level attained to date for the biotechnological production of vanillin using recombinant cells.

Role of pretreatment with acid and base on the distribution of the products obtained via lignocellulosic biomass pyrolysis

Analysis of chemicals distribution in pyrolysis liquid following different content of acid and base in pretreatment.

Bioproduction of 4-vinylphenol from corn cob alkaline hydrolyzate in two-phase extractive fermentation using free or immobilized recombinant E. coli expressing pad gene

In situ extractive fermentation was used to produce 4-vinyl derivatives from hydroxycinnamic acids extracted from corn cobs by recombinant Escherichia coli cells expressing Lactobacillus plantarum phenolic acid descarboxylase (PAD) gene. This microorganism mainly produced 4-vinylphenol (4VP) from p-coumaric acid (p-CA). In the first study , we observed that the concentrations of 4VP are higher than 1g/L which had a negative impact on decarboxylation of p-CA to 4VP by recombinant E. coli cells. Because of this, and in order to improve the downstream process, a two-phase aqueous-organic solvent system was developed. The results of the extractive fermentation indicated that it was possible to use hydrolyzates as aqueous phase to bioproduce 4VP, and recover simultaneously the product in the organic phase containing hexane. The detoxification of pre-treated corn cob alkaline hydrolyzate improved 4VP production up to 1003.5mg/L after 24h fermentation (QP=41.813mg/Lh). Additionally, preliminary experiments using cells immobilized in calcium alginate showed to be a good system for the biotransform of p-CA to 4VP in extractive fermentation, although the process hindered partially the recovery of 4VP in the organic phase.

Production of vinyl derivatives from alkaline hydrolysates of corn cobs by recombinant Escherichia coli containing the phenolic acid decarboxylase from Lactobacillus plantarum CECT 748T

The enzyme PAD from Lactobacillus plantarum CECT 748T decarboxylates some cinnamic acids namely p-coumaric acid (p-CA), caffeic acid (CA), and ferulic acid (FA) into their corresponding 4-vinyl derivatives (4-VD): 4-vinyl phenol (4-VP), 4-vinyl catechol (4-VC), and 4-vinyl guaiacol (4-VG), respectively, which are valuable food additives mainly employed as flavouring agents. The gene encoding this enzyme was cloned and overexpressed in Escherichia coli. Recombinant E. coli cells overproducing L. plantarum PAD showed a preference to degrade mainly p-CA and CA. Sterilized liquors obtained after alkaline hydrolysis of corn cob or alkaline hydrolysis of the solid residue coming from acid hydrolysis of corn cob were employed as growth media in fermentations performed in shaker or bioreactor. The fermentative process allowed converting 2222.8 mg/L p-CA into 993.9 mg/L 4-VP. The process described here allowed the production with a high-yield of a valuable food additive from a by-product of the food industry.

Recent developments in the application of Baeyer-Villiger monooxygenases as biocatalysts

Baeyer-Villiger monooxygenases (BVMOs) represent a specific class of monooxygenases that are capable of catalyzing a variety of oxidation reactions, including Baeyer-Villiger oxidations. The recently elucidated BVMO crystal structures have provided a more detailed insight into the complex mechanism of these flavin-containing enzymes. Biocatalytic studies on a number of newly discovered BVMOs have shown that they are very potent oxidative biocatalysts. In addition to catalyzing the regio- and enantioselective Baeyer-Villiger oxidations of a wide range of carbonylic compounds, epoxidations, and enantioselective sulfoxidations have also been shown to be part of their catalytic repertoire. This review provides an overview on the recent developments in BVMO-mediated biocatalytic processes, identification of the catalytic role of these enzymes in metabolic routes and prodrug activation, as well as the efforts in developing effective biocatalytic methodologies to apply BVMOs for the synthesis of high added value compounds.

Structural analysis of Bacillus pumilus phenolic acid decarboxylase, a lipocalin-fold enzyme

The decarboxylation of phenolic acids, including ferulic and p-coumaric acids, to their corresponding vinyl derivatives is of importance in the flavouring and polymer industries. Here, the crystal structure of phenolic acid decarboxylase (PAD) from Bacillus pumilus strain UI-670 is reported. The enzyme is a 161-residue polypeptide that forms dimers both in the crystal and in solution. The structure of PAD as determined by X-ray crystallography revealed a β-barrel structure and two α-helices, with a cleft formed at one edge of the barrel. The PAD structure resembles those of the lipocalin-fold proteins, which often bind hydrophobic ligands. Superposition of structurally related proteins bound to their cognate ligands shows that they and PAD bind their ligands in a conserved location within the β-barrel. Analysis of the residue-conservation pattern for PAD-related sequences mapped onto the PAD structure reveals that the conservation mainly includes residues found within the hydrophobic core of the protein, defining a common lipocalin-like fold for this enzyme family. A narrow cleft containing several conserved amino acids was observed as a structural feature and a potential ligand-binding site.

Scale-up of Baeyer-Villiger monooxygenase-catalyzed synthesis of enantiopure compounds

Several Baeyer-Villiger monooxygenases converting a wide spectrum of substrates have been discovered, cloned, and characterized throughout the last few years. Still, only a few of them are applicable for large-scale conversion predominantly due to their sensitivity towards high substrate and/or product concentrations. The recently cloned and characterized 4-hydroxyacetophenone monooxygenase from Pseudomonas putida JD1 shows excellent enantioselectivity towards 3-phenyl-2-butanone with E > 100 but is inhibited by concentrations >10 mM of both substrate and product. This obstacle could be circumvented by in situ substrate feed and product removal using a hydrophobic Lewatit® adsorbent resin. Thus, the concentration of 3-phenyl-2-butanone could be increased from 1.4 to >26 mM without significant reduction in conversion.

Extraction of phenolic acids by alkaline hydrolysis from the solid residue obtained after prehydrolysis of trimming vine shoots

Contents of hydroxycinnamic and hydroxybenzoic acids were determined in trimming vine shoots after sequential treatments of prehydrolysis and alkaline hydrolysis. These treatments allow the complete use of the main fractions involved: cellulose, hemicelluloses and lignin. The alkaline hydrolysis was studied using a factorial design where reaction time (in the range 30-120 min), temperature (50-130 degrees C), and NaOH concentration (4-12 wt % of solution) were the independent variables. The interrelationship between dependent and operational variables was well fitted (R(2) > 0.90) to models including linear, interaction and quadratic terms. Ferulic acid was the most abundant hydroxycinnamate with concentrations ranging from 25.7 to 141.0 mg/L followed by p-coumaric acid (15.5-31.5 mg/L). Gallic acid was the hydroxybenzoic acid released in higher concentration (in the range 2.5-164.6 mg/L). Because of their properties and low toxicity, these compounds are widely used in the food, pharmaceutical and cosmetic industries. Additionally, ferulic acid is used as feedstock for the biotechnological production of flavorings and aroma compounds, including vanillin and vinylguaiacol, or as a constituent in the preparation of foods and skin protection agents, or as a cross-linking agent for the elaboration of food gels. Consequently, ferulic acid solutions can be obtained from renewable plant cell wall materials as a prospective pathway.