Biotransformation of ferulic acid to vanillin in the packed bed-stirred fermentors

Production, extraction, and authentication of natural and non-natural vanillin. A comprehensive review and economic future biotechnology perspectives

Vanillin is a chief flavoring agent owing to its immense popularity in food, beverage, and pharmaceutical industries. This study holistically dissects vanillin quality control approaches that include conventional, hyphenated, and sensory analyses. Markers to differentiate between authentic, synthetic, and adulterated vanilla are highlighted using hyphenated techniques. Carbon isotope ratio range appears of potential to identify vanillin originating from biosynthetic (C3 plant), synthetic (petroleum) sources, or vanilla pods. Novel extraction methods typically provide greater selectivity, higher purity, shorter extraction times, and ecofriendly attributes compared to conventional methods. Best methods include supercritical fluids (SCF) or natural deep eutectic solvents (NADES) that promoted higher yield of vanillin. The review also highlights the promising avenue of biotransformation, the safest technique for the production of vanilla flavor components, tackling current challenges and emphasizing its potential to meet the market needs for authenticated and high-quality yields of vanillin.

Expression of a Recombinant Cholesterol Esterase from Mustela putorius furo in Pichia pastoris and Its Applicability for γ-Oryzanol Hydrolysis

Ferulic acid (FA) exhibits antioxidant and anti-inflammatory properties, making it valuable for numerous industrial applications. Traditionally, FA is produced by the alkaline hydrolysis of γ-oryzanol, which is typically associated with wastewater generation. Recently, an increasing demand of natural FA necessitates its green production via enzymatic hydrolysis of γ-oryzanol, a mixture comprising triterpene alcohol ferulates and phytosteryl ferulates. Thus far, γ-oryzanol can be hydrolyzed by only four commercial cholesterol esterases with low yields. Herein, we report a recombinant cholesterol esterase from Mustela putorius furo (MPFCE) for the enzymatic hydrolysis of γ-oryzanol. The enzyme yielded 25.5% FA, which is the highest reported through enzymatic means thus far. The hydrolysis profile revealed that the enhanced yield primarily resulted from the near-complete hydrolysis of phytosteryl ferulates, together with slight hydrolysis of triterpene alcohol ferulates. MPFCE serves as a potential candidate for the enzymatic production of FA through targeted hydrolysis of γ-oryzanol.

Optimizing bio-vanillin synthesis from ferulic acid via Pediococcus acidilactici: A systematic approach to process enhancement and yield maximization

The use of lignocellulosic biomass to create natural flavor has drawn attention from researchers. A key flavoring ingredient that is frequently utilized in the food industry is vanillin. In this present study, Pediococcus acidilactici PA VIT effectively involved in the production of bio-vanillin by using Ferulic acid as an intermediate with a yield of 11.43 µg/mL. The bio-vanillin produced by Pediococcus acidilactici PA VIT was examined using FTIR, XRD, HPLC, and SEM techniques. These characterizations exhibited a unique fingerprinting signature like that of standard vanillin. Additionally, the one variable at a time method, placket Burmann method, and response surface approach, were employed to optimize bio-vanillin. Based on the central composite rotary design, the most important process factors were determined such as agitation speed, substrate concentration, and inoculum size. After optimization, bio-vanillin was found to have tenfold increase, with a maximum yield of 376.4 µg/mL obtained using the response surface approach. The kinetic study was performed to analyze rate of reaction and effect of metal ions in the production of bio-vanillin showing Km of 10.25, and Vmax of 1250 were required for the reaction. The metal ions that enhance the yield of bio-vanillin are Ca2+, k+, and Mg2+ and the metal ions that affects the yield of bio-vanillin are Pb+ and Cr+ were identified from the effect of metal ions in the bio-vanillin production.

A comprehensive review of eclectic approaches to the biological synthesis of vanillin and their application towards the food sector

Vanillin, a highly regarded flavor compound, has earned widespread recognition for its natural and aromatic qualities, piquing substantial interest in the scientific community. This comprehensive review delves deeply into the intricate world of vanillin synthesis, encompassing a wide spectrum of methodologies, including enzymatic, microbial, and immobilized systems. This investigation provides a thorough analysis of the precursors of vanillin and also offers a comprehensive overview of its transformation through these diverse processes, making it an invaluable resource for researchers and enthusiasts alike. The elucidation of different substrates such as ferulic acid, eugenol, veratraldehyde, vanillic acid, glucovanillin, and C6-C3 phenylpropanoids adds a layer of depth and insight to the understanding of vanillin synthesis. Moreover, this comprehensive review explores the multifaceted applications of vanillin within the food industry. While commonly known as a flavoring agent, vanillin transcends this role by finding extensive use in food preservation and food packaging. The review meticulously examines the remarkable preservative properties of vanillin, providing a profound understanding of its crucial role in the culinary and food science sectors, thus making it an indispensable reference for professionals and researchers in these domains.

Graphical abstract

Biotransformation of maize bran-derived ferulic acid to vanillin using an adapted strain of Amycolatopsis sp. ATCC 39116

Maize bran, an agro-processing waste residue, is a good source of ferulic acid that can be further valorized for vanillin production. However, extraction of ferulic acid from natural sources has been challenging due to low concentrations and intensive extraction procedures. In the present work, ferulic acid streams (purities ranging from 5% to 75%) extracted from maize bran using thermochemical methods were evaluated for biotransformation to vanillin, employing Amycolatopsis sp. as a whole-cell biocatalyst. Initial adaptation studies were critical in improving ferulic acid assimilation and its conversion to vanillin by 65% and 56%, respectively by the fourth adaptation cycle. The effect of cell's physiological states and vanillic acid supplementation on vanillin production was studied using standard ferulic acid as a substrate in an effort to achieve further improvement in vanillin yield. In the presence of vanillic acid, 18 h cultured cells using 2 g/L of standard and isolated ferulic acid produced vanillin concentrations of up to 0.71 and 0.48 g/L, respectively. Furthermore, intermediates involved in the ferulic acid catabolic pathway and their interrelations were studied using GC-MS analysis. Results indicated that two different routes were involved in the catabolism of standard ferulic acid, and similar metabolic routes were observed for an isolated ferulic acid stream. These findings effectively evaluated isolated ferulic acid for sustainable vanillin production while reducing agro-industrial waste pollution.

Designing a Model-Driven Approach Towards Rational Experimental Design in Bioprocess Optimization

To enable a more rational optimization approach to drive the transition from lab-scale to large industrial bioprocesses, a systematic framework coupling both experimental design and integrated modeling was established to guide the workflow executed from small flask scale to bioreactor scale. The integrated model relies on the coupling of biotic cell factory kinetics to the abiotic bioreactor hydrodynamics to offer a rational means for an in-depth understanding of two-way spatiotemporal interactions between cell behaviors and environmental variations. This model could serve as a promising tool to inform experimental work with reduced efforts via full-factorial in silico predictions. This chapter thus describes the general workflow involved in designing and applying this modeling approach to drive the experimental design towards rational bioprocess optimization.

Improving physicochemical properties and pharmacological activities of ternary co-amorphous systems

The formation of co-amorphous by combining low molecular weight compounds with drugs is a relatively new technology in the pharmaceutical field, which can significantly improve the solubility, dissolution, and stability of poorly water-soluble drugs. However, in our previous studies, the binary co-amorphous system of andrographolide-oxymatrine (AP-OMT) was found to have obvious recrystallization and poor dissolution behavior. Therefore, in this study, we designed three stable ternary co-amorphous systems to improve the physicochemical properties of the binary co-amorphous system of AP-OMT. The ternary co-amorphous systems were prepared with AP, OMT, and trans-cinnamic acid (CA), p-hydroxycinnamic acid (pHCA), or ferulic acid (FA). Intermolecular hydrogen bonds were confirmed by spectroscopy and molecular dynamics simulation. Solubility studies showed that the solubility of the ternary co-amorphous systems of AP-OMT-CA/pHCA/FA was significantly increased compared with that of crystalline AP. Dissolution experiments suggested that the ternary co-amorphous systems of AP-OMT-CA/pHCA/FA exhibited better dissolution behavior without significant recrystallization compared to the binary co-amorphous AP-OMT. The stability study confirmed that the ternary co-amorphous system of AP-OMT-CA/pHCA/FA maintained good physical stability in the long term for 18 months. In addition, pharmacological experiments revealed that the ternary co-amorphous systems of AP-OMT-CA/pHCA/FA have an excellent safety profile and its anti-Alzheimer's disease effects are significantly improved compared to that of the binary co-amorphous systems of AP-OMT. Moreover, this study also found that reducing the pKa value of low molecular weight co-formers would affect the intermolecular interactions and improve the solubility of drugs in the ternary co-amorphous systems. In conclusion, we have successfully prepared ternary co-amorphous systems of AP-OMT-CA/pHCA/FA by amorphization technique, which improves the physicochemical properties of the binary co-amorphous systems of AP-OMT and anti-Alzheimer's disease activity in the Caenorhabditis elegans model. The mechanism for the influence of the pKa value of the co-formers on the physicochemical properties of the ternary co-amorphous system was preliminarily explored, providing theoretical guidance for the development of the ternary co-amorphous system.

Development of fluorescence sensors with copper-based nanoclusters via Förster resonance energy transfer and the quenching effect for vanillin detection

Two kinds of copper-based metal fluorescent nanoclusters were successfully prepared by the chemical reduction method; one of them (CuNCs) was synthesized by direct reduction of copper sulfate, and the other (CuAuNCs) was synthesized by the stepwise addition of copper salt and chloroauric acid. CuNCs were used to establish the fluorescence resonance energy transfer (FRET) system with neutral red (NR) due to the supramolecular effect of β-cyclodextrin (β-CD) modified on the surface of CuNCs. NR could enter the hydrophobic cavity of β-CD and narrow the distance between CuNCs and NR, which could lead to FRET. Fluorescence was transferred from CuNCs to NR, resulting in amplification of the NR fluorescence signal, which could be used to detect vanillin. In addition, CuAuNCs with strong fluorescence were used as fluorescent probes to detect vanillin through the quenching mechanism. By comparison, the simplicity of CuNC synthesis and the high selectivity of β-CD made the FRET method more practical, which may provide a new strategy for assaying vanillin.

Biotransformation of Agricultural By-Products into Biovanillin through Solid-State Fermentation (SSF) and Optimization of Different Parameters Using Response Surface Methodology (RSM)

Vanillin is a flavorful and aromatic secondary metabolite found in vanilla plants. Natural vanillin, produced through processed vanilla beans accounts for scarcely 0.2% of industrial requirements. Vanillin produced via chemical methods and microbial fermentation fills the remaining gap. Among naturally available precursors for biovanillin synthesis, ferulic acid is widely used because of its structural similarity and abundant availability. Herein, various agricultural lignocellulosic by-products (sugarcane bagasse, wheat straw, rice straw, rice bran, and corn cob) were scrutinized for their ferulic acid content, and their biotransformation into biovanillin was examined by solid-state fermentation (SSF). Then, different physicochemical parameters, i.e., moisture content, pH, temperature, inoculum size, and incubation days, were optimized to achieve a high yield of biovanillin using central composite design (CCD) of response surface methodology (RSM). Among agricultural by-products tested, sugarcane bagasse produced 0.029 g/100 g of biovanillin using Enterobacter hormaechei through SSF. After optimization, the highest concentration of biovanillin (0.476 g/100 g) was achieved at a moisture content of 70%, temperature of 37.5 °C, pH 7.5, inoculum size of 4 mL and incubation time of 48 h. The F-value of 6.10 and p-value of 0.002 evidenced the ultimate significance of the model. The significance of the constructed model was supported by the 91.73% coefficient of determination (R2), indicating that the effects of moisture, pH, and temperature were significant. HPLC and FTIR confirmed the sample identification and purity (was reported to be 98.3% pure). In conclusion, sugarcane bagasse appears to be a cost-effective substrate choice for large-scale biovanillin production.

Valorization of Fruit Peels into Biovanillin and Statistical Optimization of Process Using Enterobacter hormaechei through Solid-State Fermentation

Vanillin is a secondary metabolite of plants and the major organoleptic aroma component of natural vanilla. Nowadays, the chemical synthesis method used for vanillin production has been rejected by the United States and European legislation, while plant-derived vanillin is expensive. The current study demonstrates vanillin production via solid-state fermentation (SSF) by Enterobacter hormaechei using different ferulic acid-rich fruit peels as substrates. From different ferulic acid-rich fruit peels (pomegranate, banana, and orange) screened Punica granatum (pomegranate) peels yielded maximum biovanillin (0.09 mg/g) after 24 h. Different bioprocess parameters, including moisture content, inoculum size, pH, and temperature, were optimized using central composite design (CCD) of the response surface methodology (RSM). The maximum biovanillin yield (0.462 mg/g) from Punica granatum peels was achieved at 60% moisture content, 2 mL inoculum size, 6.5 pH, and 32 °C temperature. An F-value of 12.94 and a p-value of 0.00 were recorded by the variance analysis indicated the proposed model’s significance. The coefficient of determination (R2) confirmed the model’s goodness of fit, having a value of 91.89%, which indicated the model’s accuracy. The optimally produced biovanillin was extracted and confirmed using FTIR. Further purity analysis was done by HPLC and the biovanillin was reported to be 99.2% pure. The results demonstrated that microbial conversion of ferulic acid-rich fruit peels to biovanillin offers a cost-effective approach for the industrial production of biovanillin.

One-pot microbial bioconversion of wheat bran ferulic acid to biovanillin

Due to growing consumer preference towards natural ingredients in food products, the production of flavors by microbial biotransformation of agrowastes provides an eco-friendly, cost-effective and sustainable pathway for biovanillin production. In the present study, biovanillin was produced by microbial biotransformation of ferulic acid (FA) using Streptomyces sp. ssr-198. The strain was able to grow in glucose medium supplemented with 1 g/L FA and produce 20.91 ± 1.11 mg/L vanillin within 96 h, along with 5.78 ± 0.13 mg/L vanillic acid in 144 h. Estimation of enzymes involved in FA degradation detected maximum feruloyl-CoA synthetase activity (1.21 ± 0.03 U/mg protein) at 96 h and maximum vanillin dehydrogenase activity (0.31 ± 0.008 U/mg protein) at 168 h, with small amounts of ferulic acid esterase activity (0.13 ± 0.002 U/mg protein) in the fermentation medium. Further, the glucose deficient production medium supplemented with 3 g/L of ferulic acid when inoculated with Streptomyces sp. ssr-198 (6% wet weight) produced maximum vanillin (685 ± 20.11 mg/L) within 72 h at 37 °C under agitation (150 rpm) and declined thereafter. Furthermore, in a one-pot experiment, wherein crude ferulic acid esterase (700 IU/g of substrate) from Enterococcus lactis SR1 was added into 10% w/v wheat bran (natural source of ferulic acid) based medium and was inoculated with 1% w/v of Streptomyces sp. ssr-198 resulted in maximum vanillin production (1.02 ± 0.02 mg/g of substrate) within 60 h of incubation. The study provides an insight into synergistic effect of using FAE of E. lactis SR1 and Streptomyces sp. ssr-198 for bioproduction of biovanillin using agro residues.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-021-03006-0.

Advances in engineered Bacillus subtilis biofilms and spores, and their applications in bioremediation, biocatalysis, and biomaterials

Bacillus subtilis is a commonly used commercial specie with broad applications in the fields of bioengineering and biotechnology. B. subtilis is capable of producing both biofilms and spores. Biofilms are matrix-encased multicellular communities that comprise various components including exopolysaccharides, proteins, extracellular DNA, and poly-γ-glutamic acid. These biofilms resist environmental conditions such as oxidative stress and hence have applications in bioremediation technologies. Furthermore, biofilms and spores can be engineered through biotechnological techniques for environmentally-friendly and safe production of bio-products such as enzymes. The ability to withstand with harsh conditions and producing spores makes Bacillus a suitable candidate for surface display technology. In recent years, the spores of such specie are widely used as it is generally regarded as safe to use. Advances in synthetic biology have enabled the reprogramming of biofilms to improve their functions and enhance the production of value-added products. Globally, there is increased interest in the production of engineered biosensors, biocatalysts, and biomaterials. The elastic modulus and gel properties of B. subtilis biofilms have been utilized to develop living materials. This review outlines the formation of B. subtilis biofilms and spores. Biotechnological engineering processes and their increasing application in bioremediation and biocatalysis, as well as the future directions of B. subtilis biofilm engineering, are discussed. Furthermore, the ability of B. subtilis biofilms and spores to fabricate functional living materials with self-regenerating, self-regulating and environmentally responsive characteristics has been summarized. This review aims to resume advances in biological engineering of B. subtilis biofilms and spores and their applications.

Antifungal Activity against Botryosphaeriaceae Fungi of the Hydro-Methanolic Extract of Silybum marianum Capitula Conjugated with Stevioside

Silybum marianum (L.) Gaertn, viz. milk thistle, has been the focus of research efforts in the past few years, albeit almost exclusively restricted to the medicinal properties of its fruits (achenes). Given that other milk thistle plant organs and tissues have been scarcely investigated for the presence of bioactive compounds, in this study, we present a phytochemical analysis of the extracts of S. marianum capitula during the flowering phenological stage (stage 67). Gas chromatography–mass spectroscopy results evidenced the presence of high contents of coniferyl alcohol (47.4%), and secondarily of ferulic acid ester, opening a new valorization strategy of this plant based on the former high-added-value component. Moreover, the application of the hydro-methanolic extracts as an antifungal agent has been also explored. Specifically, their activity against three fungal species responsible for the so-called Botryosphaeria dieback of grapevine (Neofusicoccum parvum, Dothiorella viticola and Diplodia seriata) has been assayed both in vitro and in vivo. From the mycelial growth inhibition assays, the best results (EC₉₀ values of 303, 366, and 355 μg·mL⁻¹ for N. parvum, D. viticola, and D. seriata, respectively) were not obtained for the hydroalcoholic extract alone, but after its conjugation with stevioside, which resulted in a strong synergistic behavior. Greenhouse experiments confirmed the efficacy of the conjugated complexes, pointing to the potential of the combination of milk thistle extracts with stevioside as a promising plant protection product in organic Viticulture.

An integrative approach to improving the biocatalytic reactions of whole cells expressing recombinant enzymes

Biotransformation is a selective, stereospecific, efficient, and environment friendly method, compared to chemical synthesis, and a feasible tool for industrial and pharmaceutical applications. The design of biocatalysts using enzyme engineering and metabolic engineering tools has been widely reviewed. However, less importance has been given to the biocatalytic reaction of whole cells expressing recombinant enzymes. Along with the remarkable development of biotechnology tools, a variety of techniques have been applied to improve the biocatalytic reaction of whole cell biotransformation. In this review, techniques related to the biocatalytic reaction are examined, reorganized, and summarized via an integrative approach. Moreover, equilibrium-shifted biotransformation is reviewed for the first time.

Mechanochemical Preparation of Magnetically Separable Fe and Cu-Based Bimetallic Nanocatalysts for Vanillin Production

A highly sustainable method for the preparation of supported iron oxide and copper nanoparticles (NPs) on a biomass-derived carbon by solvent-free mechanochemical process is reported. In-situ mechanochemically obtained extracts from orange peel could behave as a green reducing agent, allowing the formation of Cu metal nanoparticles as well as generating a magnetic phase (magnetite) in the systems via partial Fe3+ reduction. At the same time, orange peel residues also served as template and carbon source, adding oxygen functionalities, which were found to benefit the catalytic performance of mechanochemically synthesized nanomaterials. The series of magnetic Cu-Fe@OP were tested in the oxidation of trans-ferulic acid towards vanillin, remarkably revealing a maximum vanillin yield of 82% for the sample treated at 200 °C.

Nano-Magnetic NiFe2O4 and Its Photocatalytic Oxidation of Vanillyl Alcohol-Synthesis, Characterization, and Application in the Valorization of Lignin

Here, we report on a phyto-mediated bimetallic (NiFe₂O₄) preparation using a Boswellia carterii extract, which was characterized by XRD, FT-IR, TGA, electron microscopy, magnetic spectroscopy, and Mössbauer spectroscopy measurements. The prepared nano-catalysts were tested for oxidation of lignin monomer molecules-vanillyl alcohol and cinnamyl alcohol. In comparison with previously reported methods, the nano NiFe₂O₄ catalysts showed high photocatalytic activity and selectivity, under visible light irradiation with a nitroxy radical initiator (2,2,6,6-tetramethylpiperidinyloxy or 2,2,6,6-tetramethylpiperidine 1-oxyl; TEMPO) at room temperature and aerobic conditions. The multifold advantages of the catalyst both in terms of reduced catalyst loading and ambient temperature conditions were manifested by higher conversion of the starting material.

Microbial conversion of vanillin from ferulic acid extracted from raw coir pith

Coir pith, an agro-industrial residue, is resistant to natural degradation, and its accumulation causes environmental pollution. Ferulic acid, a precursor of vanillin, was extracted from the raw coir pith by chemical pre-treatment such as alkaline hydrolysis, acidification, and liquid-liquid extraction method. The obtained ferulic acid (1.2 g/50 g) was analysed using high-performance liquid chromatography (HPLC) and used as a substrate for biotransformation by Aspergillus niger to vanillic acid, which, in turn, was fermented by using Phanerochaete chrysosporium to vanillin. The quantity of vanillic acid detected by HPLC on the third day of incubation was 0.773 g/L, while the optimal yield of vanillin on the subsequent third day of incubation was 0.628 g/L. Thus, the chemical extraction of ferulic acid from coir pith ensued bioconversion into vanillin. These products are highly valuable and economical to be used in industries such as pharmaceuticals, health, cosmetics, and neutraceuticals.

A model-driven approach towards rational microbial bioprocess optimization

Due to sustainability concerns, bio-based production capitalizing on microbes as cell factories is in demand to synthesize valuable products. Nevertheless, the nonhomogenous variations of the extracellular environment in bioprocesses often challenge the biomass growth and the bioproduction yield. To enable a more rational bioprocess optimization, we have established a model-driven approach that systematically integrates experiments with modeling, executed from flask to bioreactor scale, and using ferulic acid to vanillin bioconversion as a case study. The impacts of mass transfer and aeration on the biomass growth and bioproduction performances were examined using minimal small-scale experiments. An integrated model coupling the cell factory kinetics with the three-dimensional computational hydrodynamics of bioreactor was developed to better capture the spatiotemporal distributions of bioproduction. Full-factorial predictions were then performed to identify the desired operating conditions. A bioconversion yield of 94% was achieved, which is one of the highest for recombinant Escherichia coli using ferulic acid as the precursor.

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.

Alkaliphiles: The Versatile Tools in Biotechnology

The extreme environments within the biosphere are inhabited by organisms known as extremophiles. Lately, these organisms are attracting a great deal of interest from researchers and industrialists. The motive behind this attraction is mainly related to the desire for new and efficient products of biotechnological importance and human curiosity of understanding nature. Organisms living in common "human-friendly" environments have served humanity for a very long time, and this has led to exhaustion of the low-hanging "fruits," a phenomenon witnessed by the diminishing rate of new discoveries. For example, acquiring novel products such as drugs from the traditional sources has become difficult and expensive. Such challenges together with the basic research interest have brought the exploration of previously neglected or unknown groups of organisms. Extremophiles are among these groups which have been brought to focus and garnering a growing importance in biotechnology. In the last few decades, numerous extremophiles and their products have got their ways into industrial, agricultural, environmental, pharmaceutical, and other biotechnological applications.Alkaliphiles, organisms which thrive optimally at or above pH 9, are one of the most important classes of extremophiles. To flourish in their extreme habitats, alkaliphiles evolved impressive structural and functional adaptations. The high pH adaptation gave unique biocatalysts that are operationally stable at elevated pH and several other novel products with immense biotechnological application potential. Advances in the cultivation techniques, success in gene cloning and expression, metabolic engineering, metagenomics, and other related techniques are significantly contributing to expand the application horizon of these remarkable organisms of the 'bizarre' world. Studies have shown the enormous potential of alkaliphiles in numerous biotechnological applications. Although it seems just the beginning, some fantastic strides are already made in tapping this potential. This work tries to review some of the prominent applications of alkaliphiles by focusing such as on their enzymes, metabolites, exopolysaccharides, and biosurfactants. Moreover, the chapter strives to assesses the whole-cell applications of alkaliphiles including in biomining, food and feed supplementation, bioconstruction, microbial fuel cell, biofuel production, and bioremediation.

Genomic analysis of Burkholderia sp. ISTR5 for biofunneling of lignin-derived compounds

BACKGROUND

Lignin is the second most abundant natural polymer on earth. Industries using lignocellulosic biomass as feedstock generate a considerable amount of lignin as a byproduct with minimal usage. For a sustainable biorefinery, the lignin must be utilized in improved ways. Lignin is recalcitrant to degradation due to the complex and heterogeneous structure. The depolymerization of lignin and its conversion into specific product stream are the major challenges associated with lignin valorization. The blend of oligomeric, dimeric and monomeric lignin-derived compounds (LDCs) generated during depolymerization can be utilized by microbes for production of bioproducts.

RESULTS

In the present study, a novel bacterium Burkholderia sp. strain ISTR5 (R5), a proteobacteria belonging to class betaproteobacteria, order Burkholderiales and family Burkholderiaceae, was isolated and characterized for the degradation of LDCs. R5 strain was cultured on 12 LDCs in mineral salt medium (MSM) supplemented with individual compounds such as syringic acid, p-coumaric acid, ferulic acid, vanillin, vanillic acid, guaiacol, 4-hydroxybenzoic acid, gallic acid, benzoic acid, syringaldehyde, veratryl alcohol and catechol. R5 was able to grow and utilize all the selected LDCs. The degradation of selected LDCs was monitored by bacterial growth, total organic carbon (TOC) removal and UV-Vis absorption spectra in scan mode. TOC reduction shown in the sample contains syringic acid 80.7%, ferulic acid 84.1%, p-coumaric acid 85.9% and benzoic acid 83.2%. In UV-Vis absorption spectral scan, most of the lignin-associated peaks were found at or near 280 nm wavelength in the obtained absorption spectra. Enzyme assay for the ligninolytic enzymes was also performed, and it was observed that lignin peroxidase and laccase were predominantly expressed. Furthermore, the GC-MS analysis of LDCs was performed to identify the degradation intermediates from these compounds. The genomic analysis showed the robustness of this strain and identified various candidate genes responsible for the degradation of aromatic or lignin derivatives, detoxification mechanism, oxidative stress response and fatty acid synthesis. The presence of peroxidases (13%), laccases (4%), monooxygenases (23%), dioxygenase (44%), NADPH: quinone oxidoreductases (16%) and many other related enzymes supported the degradation of LDCs.

CONCLUSION

Numerous pathway intermediates were observed during experiment. Vanillin was found during growth on syringic acid, ferulic acid and p-coumaric acid. Some other intermediates like catechol, acetovanillone, syringaldehyde and 3,4-dihydroxybenzaldehyde from the recognized bacterial metabolic pathways existed during growth on the LDCs. The ortho- and meta cleavage pathway enzymes, such as the catechol-1,2-dioxygenase, protocatechuate 3,4-dioxygenase, catechol-2,3-dioxygenase and toluene-2,3-dioxygenase, were observed in the genome. In addition to the common aromatic degradation pathways, presence of the epoxyqueuosine reductase, 1,2-epoxyphenylacetyl-CoA isomerase in the genome advocates that this strain may follow the epoxy Coenzyme A thioester pathway for degradation.

One-Pot Cu/TiO2 Nanoparticles Synthesis for Trans-Ferulic Acid Conversion into Vanillin

In this study, the co-synthesis of TiO₂ and Cu metallic nanoparticles obtained via one-pot cost-efficient hydrothermal process has been addressed. Different nanocatalysts with Cu contents were characterized by X-ray diffraction, nitrogen porosimetry, scanning electron microscopy, and transmission electron microscopy. The TiO₂ and Cu metallic nanoparticles were synthesized with copper loading up to one (Cu/Ti atomic ratio). Synthesized catalysts exhibited pore sizes in the mesoporous range and high surface areas above 150 m²/g. The particle size for TiO₂ presented a homogeneous distribution of approximately 8 nm, moreover, Cu nanoparticles varied from 12 to >100 nm depending on the metal loading. The nanostructured materials were successfully tested in the conversion of trans-ferulic acid into vanillin under sustainable conditions, achieving the best performance for 0.3 Cu/Ti atomic ratio (70% vanillin yield).

Comparative Studies of White-Rot Fungal Strains (Trametes hirsuta MTCC-1171 and Phanerochaete chrysosporium NCIM-1106) for Effective Degradation and Bioconversion of Ferulic Acid

Biodegradation of ferulic acid, by two white-rot fungal strains (Trametes hirsuta MTCC-1171 and Phanerochaete chrysosporium NCIM-1106) was investigated in this study. Both strains could use ferulic acid as a sole carbon source when provided with basal mineral salt medium. T. hirsuta achieved complete degradation of ferulic acid (350 mg L^-1) in 20 h, whereas P. chrysosporium degraded it (250 mg L^-1) in 28 h. The metabolites produced during degradation were distinguished by gas chromatography-mass spectrometry. Bioconversion of ferulic acid to vanillin by P. chrysosporium was also investigated. The optimum experimental conditions for bioconversion to vanillin can be summarized as follows: ferulic acid concentration 250 mg L^-1, temperature 35 °C, initial pH 5.0, mycelial inoculum 0.32 ± 0.01 g L^-1 dry weight, and shaking speed 150 rpm. At optimized conditions, the maximum molar yield obtained was 3.4 ± 0.1%, after 20 h of bioconversion. Considering that the degradation of ferulic acid was determined by laccase and lignin peroxidase to some extent, the possible role of ligninolytic enzymes in overall bioconversion process was also studied. These results illustrate that both strains have the potential of utilizing ferulic acid as a sole carbon source. Moreover, P. chrysosporium can also be explored for its ability to transform ferulic acid into value-added products.

Molecular cloning and characterization of vanillin dehydrogenase from Streptomyces sp. NL15-2K

Background

Streptomyces sp. NL15-2K, previously isolated from the forest soil, features an extensive catabolic network for lignin-derived aromatic compounds, including pathways transforming ferulic acid to vanillin, vanillic acid, and protocatechuic acid. To successfully use Streptomyces sp. NL15-2K as a biocatalyst for vanillin production, it is necessary to characterize the vanillin dehydrogenase (VDH) that degrades the produced vanillin to vanillic acid, as well as the gene encoding this enzyme. Here, we cloned the VDH-encoding gene (vdh) from strain NL15-2K and comprehensively characterized its gene product.

Results

The vdh open reading frame contains 1488 bp and encodes a 496-amino-acid protein with a calculated molecular mass of 51,705 Da. Whereas the apparent native molecular mass of recombinant VDH was estimated to be 214 kDa by gel filtration analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed a subunit molecular mass of ca. 56 kDa, indicating that VDH is a homotetramer. The recombinant enzyme showed optimal activity at 45 °C and pH 9.5. The VDH substrate specificity followed this order: vanillin (100%) > protocatechualdehyde (91%) > benzaldehyde (79%) > p-hydroxybenzaldehyde (56%) > isovanillin (49%) ≈ salicylaldehyde (48%) > anisaldehyde (15%) ≈ veratraldehyde (12%). Although peptide mass fingerprinting and BLAST searches indicated that this enzyme is a salicylaldehyde dehydrogenase (SALDH), the determined kinetic parameters clearly demonstrated that the enzyme is a vanillin dehydrogenase. Lastly, phylogenetic analysis revealed that VDH from Streptomyces sp. NL15-2K forms an independent branch in the phylogenetic tree and, hence, is evolutionarily distinct from other VDHs and SALDHs whose activities have been confirmed experimentally.

Conclusions

Our findings not only enhance the understanding of the enzymatic properties of VDH and the characteristics of its amino acid sequence, but also contribute to the development of Streptomyces sp. NL15-2K into a biocatalyst for the biotransformation of ferulic acid to vanillin.

Electronic supplementary material

The online version of this article (10.1186/s12866-018-1309-2) contains supplementary material, which is available to authorized users.

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.

Optimizing bioconversion of ferulic acid to vanillin by Bacillus subtilis in the stirred packed reactor using Box-Behnken design and desirability function

A stirring bioreactor packed with a carbon fiber textiles (FT) biofilm formed by Bacillus subtilis was used to produce vanillin from ferulic acid. Biofilm formation was characterized by scanning electron microscopy. The interactive effects of three variables on vanillin molar yield (M) and conversion efficiency of ferulic acid (E) were evaluated by response surface methodology (RSM) with a Box-Behnken design (BBD). The optimal conversion conditions with a maximum overall desirability D of 0.983 were obtained by a desirability function. Considering the actual operation, the confirmation tests were performed using the slightly modified optimal conditions (initial ferulic acid concentration 1.55 g/L, temperature 35°C, stirring speed 220 rpm). The results showed that M and E were 57.42 and 93.53%, respectively. This was only 1.03% and 1.87%, respectively, different from the predicted values, confirming the validity of the predicted models. These revealed that the stirred packed reactor could be successfully used in vanillin bioconversion from ferulic acid.