Enzymatic and whole cell catalysis: finding new strategies for old processes

Efficient production of l-glutathione by whole-cell catalysis with ATP regeneration from adenosine

l-glutathione (GSH) is an important tripeptide compound with extensive applications in medicine, food additives, and cosmetics industries. In this work, an innovative whole-cell catalytic strategy was developed to enhance GSH production by combining metabolic engineering of GSH biosynthetic pathways with an adenosine-based adenosine triphosphate (ATP) regeneration system in Escherichia coli. Concretely, to enhance GSH production in E. coli, several genes associated with GSH and  l-cysteine degradation, as well as the branched metabolic flow, were deleted. Additionally, the GSH bifunctional synthase (GshFSA) and GSH ATP-binding cassette exporter (CydDC) were overexpressed. Moreover, an adenosine-based ATP regeneration system was first introduced into E. coli to enhance GSH biosynthesis without exogenous ATP additions. Through the optimization of whole-cell catalytic conditions, the engineered strain GSH17-FDC achieved an impressive GSH titer of 24.19 g/L only after 2 h reaction, with a nearly 100% (98.39%) conversion rate from the added  l-Cys. This work not only unveils a new platform for GSH production but also provides valuable insights for the production of other high-value metabolites that rely on ATP consumption.

Six undescribed 23-norursane triterpenoids from the biotransformation of ilexgenin a by endophytic fungi and their vascular protective activity

Biotransformation of ursane-type triterpenoid ilexgenin A by endophytic fungi Lasiodiplodia sp. MQD-4 and Pestalotiopsis sp. ZZ-1, isolated from Ilex pubescences and Callicarpa kwangtungensis respectively, was investigated for the first time. Six previously undescribed metabolites (1-6) with 23-norursane triterpenoids skeleton were isolated and their structures were unambiguously established by the analysis of spectroscopic data and single-crystal X-ray crystallographic experiments. Decarboxylation, oxidation, and hydroxylation reactions were observed on the triterpenoid skeleton. Especially, the decarboxylation of C-23 provided definite evidence to understand the biogenetic process of 23-norursane triterpenoids. Moreover, the qualitative analysis of the extract of I. pubescences showed metabolites 1, 3, 4, and 6 could be detected in the originated plant, indicating biotransformation by endophytic fungi is a practical strategy for the isolation of novel natural products. Finally, all isolates were evaluated for the protective activities against H2O2-induced HUVECs dysfunction in vitro. Compound 5 could improve the viability of endothelial cells and decrease the level of intracellular ROS.

Engineering a coenzyme-independent dioxygenase for one-step production of vanillin from ferulic acid

Vanillin is one of the world's most important flavor and fragrance compounds used in foods and cosmetics. In plants, vanillin is reportedly biosynthesized from ferulic acid via the hydratase/lyase-type enzyme VpVAN. However, in biotechnological and biocatalytic applications, the use of VpVAN limits the production of vanillin. Although microbial enzymes are helpful as substitutes for plant enzymes, synthesizing vanillin from ferulic acid in one step using microbial enzymes remains a challenge. Here, we developed a single enzyme that catalyzes vanillin production from ferulic acid in a coenzyme-independent manner via the rational design of a microbial dioxygenase in the carotenoid cleavage oxygenase family using computational simulations. This enzyme acquired catalytic activity toward ferulic acid by introducing mutations into the active center to increase its affinity for ferulic acid. We found that the single enzyme can catalyze not only the production of vanillin from ferulic acid but also the synthesis of other aldehydes from p-coumaric acid, sinapinic acid, and coniferyl alcohol. These results indicate that the approach used in this study can greatly expand the range of substrates available for the dioxygenase family of enzymes. The engineered enzyme enables efficient production of vanillin and other value-added aldehydes from renewable lignin-derived compounds.

IMPORTANCE

The final step of vanillin biosynthesis in plants is reportedly catalyzed by the enzyme VpVAN. Prior to our study, VpVAN was the only reported enzyme that directly converts ferulic acid to vanillin. However, as many characteristics of VpVAN remain unknown, this enzyme is not yet suitable for biocatalytic applications. We show that an enzyme that converts ferulic acid to vanillin in one step could be constructed by modifying a microbial dioxygenase-type enzyme. The engineered enzyme is of biotechnological importance as a tool for the production of vanillin and related compounds via biocatalytic processes and metabolic engineering. The results of this study may also provide useful insights for understanding vanillin biosynthesis in plants.

State-of-the-art strategies and research advances for the biosynthesis of D-amino acids

D-amino acids (D-AAs) are the enantiomeric counterparts of L-amino acids (L-AAs) and important functional factors with a wide variety of physiological activities and applications in the food manufacture industry. Some D-AAs, such as D-Ala, D-Leu, and D-Phe, have been favored by consumers as sweeteners and fragrances because of their unique flavor. The biosynthesis of D-AAs has attracted much attention in recent years due to their unique advantages. In this review, we comprehensively analyze the structure-function relationships, biosynthesis pathways, multi-enzyme cascade and whole-cell catalysis for the production of D-AAs. The state-of-the-art strategies, including immobilization, protein engineering, and high-throughput screening, are summarized. Future challenges and perspectives of strategies-driven by bioinformatics technologies and smart computing technologies, as well as enzyme immobilization, are also discussed. These new approaches will promote the commercial production and application of D-AAs in the food industry by optimizing the key enzymes for industrial biocatalysts.

Recent advances in electrochemical cell-based biosensors for food analysis: Strategies for sensor construction

Owing to their advantages such as great specificity, sensitivity, rapidity, and possibility of noninvasive and real-time monitoring, electrochemical cell-based biosensors (ECBBs) have been a powerful tool for food analysis encompassing the areas of nutrition, flavor, and safety. Notably, the distinctive biological relevance of ECBBs enables them to mimic physiological environments and reflect cellular behaviors, leading to valuable insights into the biological function of target components in food. Compared with previous reviews, this review fills the current gap in the narrative of ECBB construction strategies. The review commences by providing an overview of the materials and configuration of ECBBs, including cell types, cell immobilization strategies, electrode modification materials, and electrochemical sensing types. Subsequently, a detailed discussion is presented on the fabrication strategies of ECBBs in food analysis applications, which are categorized based on distinct signal sources. Lastly, we summarize the merits, drawbacks, and application scope of these diverse strategies, and discuss the current challenges and future perspectives of ECBBs. Consequently, this review provides guidance for the design of ECBBs with specific functions and promotes the application of ECBBs in food analysis.

Strategies for the biological synthesis of D-glucuronic acid and its derivatives

D-glucuronic acid is a kind of glucose derivative, which has excellent properties such as anti-oxidation, treatment of liver disease and hyperlipidemia, and has been widely used in medicine, cosmetics, food and other fields. The traditional production methods of D-glucuronic acid mainly include natural extraction and chemical synthesis, which can no longer meet the growing market demand. The production of D-glucuronic acid by biocatalysis has become a promising alternative method because of its high efficiency and environmental friendliness. This review describes different production methods of D-glucuronic acid, including single enzyme catalysis, multi-enzyme cascade, whole cell catalysis and co-culture, as well as the intervention of some special catalysts. In addition, some feasible enzyme engineering strategies are provided, including the application of enzyme immobilized scaffold, enzyme mutation and high-throughput screening, which provide good ideas for the research of D-glucuronic acid biocatalysis.

A sustainable strategy for biosynthesis of Rebaudioside D using a novel glycosyltransferase of Solanum tuberosum

Bioconversion of Rebaudioside D faces high-cost obstacles. Herein, a novel glycosyltransferase StUGT converting Rebaudioside A to Rebaudioside D was screened and characterized, which exhibits stronger affinity and substrate specificity for Rebaudioside A than previously reported enzymes. A whole-cell catalytic system was thus developed using the StUGT strain. The production of Rebaudioside D was enhanced significantly by enhancing cell permeability, and the maximum production of 6.12 g/L and the highest yield of 98.08% by cell catalyst was obtained by statistical-based optimization. A new cascade process utilizing this recombinant strain and E. coli expressing sucrose synthase was further established to reduce cost through replacing expensive UDPG with sucrose. A StUGT-GsSUS1 system exhibited high catalytic capability, and 5.27 g L-1 Rebaudioside D was achieved finally without UDPG addition by systematic optimization. This is the best performance reported in cell-cascaded biosynthesis, which paves a new cost-effective strategy for sustainable synthesis of scarce premium sweeteners from biomass.

Identification of a novel thermostable transaminase and its application in L-phosphinothricin biosynthesis

Transaminase (TA) is a crucial biocatalyst for enantioselective production of the herbicide L-phosphinothricin (L-PPT). The use of enzymatic cascades has been shown to effectively overcome the unfavorable thermodynamic equilibrium of TA-catalyzed transamination reaction, also increasing demand for TA stability. In this work, a novel thermostable transaminase (PtTA) from Pseudomonas thermotolerans was mined and characterized. The PtTA showed a high specific activity (28.63 U/mg) towards 2-oxo-4-[(hydroxy)(methyl)phosphinoyl]butyric acid (PPO), with excellent thermostability and substrate tolerance. Two cascade systems driven by PtTA were developed for L-PPT biosynthesis, including asymmetric synthesis of L-PPT from PPO and deracemization of D, L-PPT. For the asymmetric synthesis of L-PPT from PPO, a three-enzyme cascade was constructed as a recombinant Escherichia coli (E. coli G), by co-expressing PtTA, glutamate dehydrogenase (GluDH) and D-glucose dehydrogenase (GDH). Complete conversion of 400 mM PPO was achieved using only 40 mM amino donor L-glutamate. Furthermore, by coupling D-amino acid aminotransferase (Ym DAAT) from Bacillus sp. YM-1 and PtTA, a two-transaminase cascade was developed for the one-pot deracemization of D, L-PPT. Under the highest reported substrate concentration (800 mM D, L-PPT), a 90.43% L-PPT yield was realized. The superior catalytic performance of the PtTA-driven cascade demonstrated that the thermodynamic limitation was overcome, highlighting its application prospect for L-PPT biosynthesis. KEY POINTS: • A novel thermostable transaminase was mined for L-phosphinothricin biosynthesis. • The asymmetric synthesis of L-phosphinothricin was achieved via a three-enzyme cascade. • Development of a two-transaminase cascade for D, L-phosphinothricin deracemization.

MpADC, an L-aspartate-α-decarboxylase, from Myzus persicae, that enables production of β-alanine with high yield by whole-cell enzymatic catalysis

BACKGROUND

β-Alanine is a precursor of many important pharmaceutical products and food additives, its market demand is continuously increasing nowadays. Whole-cell catalysis relying on the recombinant expression of key β-alanine synthesizing enzymes is an important method to produce β-alanine. Nevertheless, β-alanine synthesizing enzymes found so far have problems including easy inactivation, low expression or poor catalytic activity, and it remains necessary to develop new enzymes.

RESULTS

Herein, we characterized an L-aspartate-α-decarboxylase, MpADC, from an aphid, Myzus persicae. It showed excellent catalytic activity at pH 6.0-7.5 and 37 °C. With the help of chaperone co-expression and N-terminal engineering guided by AlphaFold2 structure prediction, the expression and catalytic ability of MpADC in Escherichia coli were significantly improved. Using 50 g/L of E. coli cells expressing the MpADC-∆39 variant cultured in a 15-L fermenter, 232.36 g/L of β-alanine was synthesized in 13.5 h, with the average β-alanine yield of 17.22 g/L/h, which is best known so far.

CONCLUSIONS

Our research should facilitate the production of β-alanine in an environment-friendly manner.

Advancements in the Biotransformation and Biosynthesis of the Primary Active Flavonoids Derived from Epimedium

Epimedium is a classical Chinese herbal medicine, which has been used extensively to treat various diseases, such as sexual dysfunction, osteoporosis, cancer, rheumatoid arthritis, and brain diseases. Flavonoids, such as icariin, baohuoside I, icaritin, and epimedin C, are the main active ingredients with diverse pharmacological activities. Currently, most Epimedium flavonoids are extracted from Epimedium plants, but this method cannot meet the increasing market demand. Biotransformation strategies promised huge potential for increasing the contents of high-value Epimedium flavonoids, which would promote the full use of the Epimedium herb. Complete biosynthesis of major Epimedium flavonoids by microbial cell factories would enable industrial-scale production of Epimedium flavonoids. This review summarizes the structures, pharmacological activities, and biosynthesis pathways in the Epimedium plant, as well as the extraction methods of major Epimedium flavonoids, and advancements in the biotransformation and complete microbial synthesis of Epimedium flavonoids, which would provide valuable insights for future studies on Epimedium herb usage and the production of Epimedium flavonoids.

Conversion of Similar Xenochemicals to Dissimilar Products: Exploiting Competing Reactions in Whole-Cell Catalysis

Many enzymes have latent activities that can be used in the conversion of non-natural reactants for novel organic conversions. A classic example is the conversion of benzaldehyde to a phenylacetyl carbinol, a precursor for ephedrine manufacture. It is often tacitly assumed that purified enzymes are more promising catalysts than whole cells, despite the lower cost and easier maintenance of the latter. Competing substrates inside the cell have been known to elicit currently hard-to-predict selectivities that are not easily measured inside the living cell. We employ NMR spectroscopic assays to rationally combine isomers for selective reactions in commercial S. cerevisiae. This approach uses internal competition between alternative pathways of aldehyde clearance in yeast, leading to altered selectivities compared to catalysis with the purified enzyme. In this manner, 4-fluorobenzyl alcohol and 2-fluorophenylacetyl carbinol can be formed with selectivities in the order of 90%. Modification of the cellular redox state can be used to tune product composition further. Hyperpolarized NMR shows that the cellular reaction and pathway usage are affected by the xenochemical. Overall, we find that the rational construction of ternary or more complex substrate mixtures can be used for in-cell NMR spectroscopy to optimize the upgrading of similar xenochemicals to dissimilar products with cheap whole-cell catalysts.

Photoenzymatic Decarboxylation to Produce Hydrocarbon Fuels: A Critical Review

Photoenzymatic decarboxylation shows great promise as a pathway for the generation of hydrocarbon fuels. CvFAP, which is derived from Chlorella variabilis NC64A, is a photodecarboxylase capable of converting fatty acids into hydrocarbons. CvFAP is an example of coupling biocatalysis and photocatalysis to produce alkanes. The catalytic process is mild, and it does not yield toxic substances or excess by-products. However, the activity of CvFAP can be readily inhibited by several factors, and further enhancement is required to improve the enzyme yield and stability. In this article, we will examine the latest advancements in CvFAP research, with a particular focus on the enzyme's structural and catalytic mechanism, summarized some limitations in the application of CvFAP, and laboratory-level methods for enhancing enzyme activity and stability. This review can serve as a reference for future large-scale industrial production of hydrocarbon fuels.

Whole-cell bioconversion using non-Leloir transglycosylation reactions: a review

Microbial biocatalysts are evolving technological tools for glycosylation research in food, feed and pharmaceuticals. Advances in bioengineered Leloir and non-Leloir carbohydrate-active enzymes allow for whole-cell biocatalysts to curtail production costs of purified enzymes while enhancing glucan synthesis through continued enzyme expression. Unlike sugar nucleotide-dependent Leloir glycosyltransferases, non-Leloir enzymes require inexpensive sugar donors and can be designed to match the high value, yield and selectivity of the former. This review addresses the current state of bacterial cell-based production of glucans and glycoconjugates via transglycosylation, and describes how alterations made to microbial hosts to surpass purified enzymes as the preferred mode of catalysis are steadily being acquired through genetic engineering, rational design and process optimization. A comprehensive exploration of relevant literature has been summarized to describe whole-cell biocatalysis in non-Leloir glycosylation reactions with various donors and acceptors, and the characterization, application and latest developments in the optimization of their use.

In-Cell NMR Approach for Real-Time Exploration of Pathway Versatility: Substrate Mixtures in Nonengineered Yeast

The central carbon metabolism of microbes will likely be used in future sustainable bioproduction. A sufficiently deep understanding of central metabolism would advance the control of activity and selectivity in whole-cell catalysis. Opposite to the more obvious effects of adding catalysts through genetic engineering, the modulation of cellular chemistry through effectors and substrate mixtures remains less clear. NMR spectroscopy is uniquely suited for in-cell tracking to advance mechanistic insight and to optimize pathway usage. Using a comprehensive and self-consistent library of chemical shifts, hyperpolarized NMR, and conventional NMR, we probe the versatility of cellular pathways to changes in substrate composition. Conditions for glucose influx into a minor pathway to an industrial precursor (2,3-butanediol) can thus be designed. Changes to intracellular pH can be followed concurrently, while mechanistic details for the minor pathway can be derived using an intermediate-trapping strategy. Overflow at the pyruvate level can be induced in nonengineered yeast with suitably mixed carbon sources (here glucose with auxiliary pyruvate), thus increasing glucose conversion to 2,3-butanediol by more than 600-fold. Such versatility suggests that a reassessment of canonical metabolism may be warranted using in-cell spectroscopy.

Highly efficient bioconversion of icariin to icaritin by whole-cell catalysis

BACKGROUND

Icaritin is an aglycone of flavonoid glycosides from Herba Epimedii. It has good performance in the treatment of hepatocellular carcinoma in clinical trials. However, the natural icaritin content of Herba Epimedii is very low. At present, the icaritin is mainly prepared from flavonoid glycosides by α-L-rhamnosidases and β-glucosidases in two-step catalysis process. However, one-pot icaritin production required reported enzymes to be immobilized or bifunctional enzymes to hydrolyze substrate with long reaction time, which caused complicated operations and high costs. To improve the production efficiency and reduce costs, we explored α-L-rhamnosidase SPRHA2 and β-glucosidase PBGL to directly hydrolyze icariin to icaritin in one-pot, and developed the whole-cell catalytic method for efficient icaritin production.

RESULTS

The SPRHA2 and PBGL were expressed in Escherichia coli, respectively. One-pot production of icaritin was achieved by co-catalysis of SPRHA2 and PBGL. Moreover, whole-cell catalysis was developed for icariin hydrolysis. The mixture of SPRHA2 cells and PBGL cells transformed 200 g/L icariin into 103.69 g/L icaritin (yield 95.23%) in 4 h in whole-cell catalysis under the optimized reaction conditions. In order to further increase the production efficiency and simplify operations, we also constructed recombinant E. coli strains that co-expressed SPRHA2 and PBGL. Crude icariin extracts were also efficiently hydrolyzed by the whole-cell catalytic system.

CONCLUSIONS

Compared to previous reports on icaritin production, in this study, whole-cell catalysis showed higher production efficiency of icaritin. This study provides promising approach for industrial production of icaritin in the future.

Recent advances and challenges in sustainable management of plastic waste using biodegradation approach

Versatility and desirable attributes of synthetic plastics have greatly contributed towards their wide applications. However, vast accumulation of plastic wastes in environment as a result of their highly recalcitrant nature has given rise to plastic pollution. Existing strategies in alleviating plastic wastes accumulation are inadequate, and there is a pressing need for alternative sustainable approaches in tackling plastic pollution. In this context, plastic biodegradation has emerged as a sustainable and environmental-friendly approach in handling plastic wastes accumulation, due to its milder and less energy-intensive conditions. In recent years, extensive research effort has focused on the identification of microorganisms and enzymes with plastic-degrading abilities. This review aims to provide a timely and holistic view on the current status of plastic biodegradation, focusing on recent breakthroughs and discoveries in this field. Furthermore, current challenges associated to plastic biodegradation are discussed, and the future perspectives for continuous advancement of plastic biodegradation are highlighted.

Green immobilization and efficient proliferation of Escherichia coli cells in polyvinyl alcohol hydrogel membranes by unidirectional nanopore dehydration

BACKGROUND

The immobilized technology for microbial or cells has the advantages of high microbial activity, high microbial density per unit space, good tolerance, strong shock, load resistance, high processing efficiency, and high reuse rate. It is now widely used in environmental remediation, water quality treatment, biodegradation, food industry, chemical analysis, energy development, medicine and pharmaceuticals, and other fields.

RESULTS

A novel Escherichia coli cell-immobilizing polyvinyl alcohol hydrogel membrane (ECI-PVAHM) was prepared by unidirectional nanopore dehydration (UND) from a 10% polyvinyl alcohol (PVA) aqueous solution containing enhanced green fluorescent protein-labeled E. coli. This bacteria-loaded film has high water stability, flexibility, transparency, and mechanical robustness. Its tensile strength, elongation rate, and swelling rate are in the ranges 0.66-0.90 MPa, 300-390%, and 330-800%, respectively. The effective bacterial load of ECI-PVAHM is 2.375 × 10⁹-10¹⁰ CFU/g (dry weight), which does not affect the original crystal structure of the PVAHM. This biofilm has a porous network structure with pore sizes between 0.2 and 1.0 μm, and these cells are embedded in the PVAHM network. When the immobilized cells were continuously cultured for 20 days, and the medium was renewed twice daily, their relative proliferation efficiency after 40 cycles could still be maintained at ~ 91%.

CONCLUSION

The above results show that the cell division, proliferation ability, and metabolic activity of immobilized E. coli were not affected by the physical barrier of the porous network structure of the hydrogel. This UND-based ECI-PVAHM has potential applications in molecular biology, biopharmaceutical expression and production, bioreactors, and fuel cells.

Rational Design of Artificial Biofilms as Sustainable Supports for Whole-Cell Catalysis Through Integrating Extra- and Intracellular Catalysis

Biofilms are promising candidates for sustainable bioprocessing applications. This work presents a rational design of biofilm catalysts by integrating extra- and intracellular catalysis systems with optimized substrate channeling to realize efficient multistep biosynthesis. An assembly of four enzymes in a "three-in-one" structure was achieved by rationally placing the enzymes on curli nanofibers, the cell surface, and inside cells. The catalytic efficiency of the biofilm catalysts was over 2.8 folds higher than that of the control whole-cell catalysis when the substrate benzaldehyde was fed at 100 mm. The highest yield of d-phenyllactic acid catalyzed by biofilm catalysts under optimized conditions was 102.19 mm, also much higher than that of the control catalysis test (52.29 mm). The results demonstrate that engineered biofilms are greatly promising in integrating extra- and intracellular catalysis, illustrating great potentials of rational design in constructing biofilm catalysts as sustainable supports for whole-cell catalysis.

ATP is not essential for cadaverine production by Escherichia coli whole-cell bioconversion

ATP plays an essential role in the substrate/product transmembrane transportation during whole-cell bioconversion. This study aimed to address the impact of ATP upon cadaverine synthesis by whole-cell biocatalysts. The results showed no significant change in the ATP content (P = 0.625), and the specific cadaverine yield (P = 0.374) was observed in enzyme-catalyzed cadaverine synthesis with exogenous addition of ATP, indicating that the enzyme-catalyzed process does not require the participation of ATP. Furthermore, a whole-cell biocatalyst co-overexpressed methionine adenosyltransferase (MetK), lysine decarboxylase (CadA), and lysine/cadaverine antiporter (CadB) was constructed and used to investigate the effect of ATP deficiency on the cadaverine production by conversion of L-methionine and L-lysine, simultaneously. The results showed no significant difference (P = 0.585) in the specific cadaverine content between high and low levels of intracellular ATP. In addition, the intra- and extracellular cadaverine concentration and the ratio of ATP/ADP of whole-cell biocatalyst were determined. Results showed that the extracellular cadaverine concentration was much higher than the intracellular concentration, and no significant changes in ATP/ADP ratio during cadaverine synthesis. In contrast, an inhibition effect of the proton motive force (PMF) inhibitor carbonyl cyanide m-chlorophenylhydrazone (CCCP) on cadaverine production was detected. These findings strongly suggest that cadaverine transport in whole-cell biocatalysts was energized by PMF rather than ATP. Finally, a model was proposed to describe cadaverine's PMF-driven transport under different external pHs during whole-cell biocatalysis. This study is the first to experimentally confirm that the cadaverine production by Escherichia coli whole-cell bioconversion is independent of intracellular ATP, which helps guide the subsequent construction of biocatalysts and optimize transformation conditions.

Alginate@polydopamine@SiO2 microcapsules with controlled porosity for whole-cell based enantioselective biosynthesis of (S)-1-phenylethanol

Whole-cell biocatalysis, owing to its high enantioselectivity, environment friendly and mild reaction condition, show a great prospect in chemical, pharmaceutical and fuel industry. However, several problems still limit its wide applications, mainly concerning the low productivity and poor stability. Although the biocatalyst encapsulated in the most-commonly-used alginate hydrogels demonstrate enhanced stability, it still suffers from low biocatalytic productivity, long-term reusability and poor mass diffusion control. In this work, hybrid alginate@polydopamine@SiO₂ microcapsules with controlled porosity are designed to encapsulate yeast cells for the asymmetric biosynthesis of (S)- 1-phenylethonal from acetophenone. The hybrid microcapsules are formed by the ionic cross-linking of alginate, the polymerization of dopamine monomers and the protamine-assisted colloidal packing of uniform-sized silica nanoparticles. Alginate provides the encapsulated cells with highly biocompatible environment. Polydopamine enables to stimulate the biocatalytic productivity of the encapsulated yeast cells. Silica shells can not only regulate the mass diffusion in biocatalysis but also enhance the long-term mechanical and chemical stability of the microcapsules. The morphology, structure, chemical composition, stability and molecular accessibility of the hybrid microcapsules are investigated in detail. The viability and asymmetric bioreduction performance of the cells encapsulated in microcapsules are evaluated. The 24 h product yield of the cells encapsulated in the hybrid microcapsules shows 1.75 times higher than that of the cells encapsulated in pure alginate microcapsules. After 6 batches, the 24 h product yield of the cells encapsulated in the hybrid microcapsules is well maintained and 2 times higher than that of the cells encapsulated in pure alginate microcapsules. Therefore, the hybrid microcapsules designed in this study enable to enhance the asymmetric biocatalytic activity, stability and reusability of the encapsulated cells, thus contributing to a significant progress in cell-encapsulating materials to be applied in biocatalytic asymmetric synthesis industry.

A Simple and Reliable Dispersive Liquid-Liquid Microextraction with Smartphone-Based Digital Images for Determination of Carbaryl Residues in Andrographis paniculata Herbal Medicines Using Simple Peroxidase Extract from Senna siamea Lam. Bark

A simple and reliable dispersive liquid-liquid microextraction (DLLME) coupled with smartphone-based digital images using crude peroxidase extracts from cassia bark (Senna siamea Lam.) was proposed to determine carbaryl residues in Andrographis paniculata herbal medicines. The method was based on the reaction of 1-naphthol (hydrolysis of carbaryl) with 4-aminoantipyrine (4-AP) in the presence of hydrogen peroxide, using peroxidase enzyme simple extracts from cassia bark as biocatalysts under pH 6.0. The red product, after preconcentration by DLLME using dichloromethane as extraction solvent, was measured for blue intensity by daily life smartphone-based digital image analysis. Under optimized conditions, good linearity of the calibration graph was found at 0.10–0.50 mg·L⁻¹ (r² = 0.9932). Limits of detection (LOD) (3SD/slope) and quantification (LOQ) (10SD/slope) were 0.03 and 0.09 mg·L⁻¹, respectively, with a precision of less than 5%. Accuracy of the proposed method as percentage recovery gave satisfactory results. The proposed method was successfully applied to analyze carbaryl in Andrographis paniculata herbal medicines. Results agreed well with values obtained from the HPLC-UV method at 95% confidence level. This was simple, convenient, reliable, cost-effective and traceable as an alternative method for the determination of carbaryl.

Process Development for Benzyl Alcohol Production by Whole-Cell Biocatalysis in Stirred and Packed Bed Reactors

The ocean is an excellent source for new biocatalysts due to the tremendous genetic diversity of marine microorganisms, and it may contribute to the development of sustainable industrial processes. A marine bacterium was isolated and selected for the conversion of benzaldehyde to benzyl alcohol, which is an important chemical employed as a precursor for producing esters for cosmetics and other industries. Enzymatic production routes are of interest for sustainable processes. To overcome benzaldehyde low water solubility, DMSO was used as a biocompatible cosolvent up to a concentration of 10% (v/v). A two-phase system with n-hexane, n-heptane, or n-hexadecane as organic phase allowed at least a 44% higher relative conversion of benzaldehyde than the aqueous system, and allowed higher initial substrate concentrations. Cell performance decreased with increasing product concentration but immobilization of cells in alginate improved four-fold the robustness of the biocatalyst: free and immobilized cells were inhibited at concentrations of benzyl alcohol of 5 and 20 mM, respectively. Scaling up to a 100 mL stirred reactor, using a fed-batch approach, enabled a 1.5-fold increase in benzyl alcohol productivity when compared with batch mode. However, product accumulation in the reactor hindered the conversion. The use of a continuous flow reactor packed with immobilized cells enabled a 9.5-fold increase in productivity when compared with the fed-batch stirred reactor system.

Immobilization of engineered E. coli cells for asymmetric reduction of methyl acetoacetate to methyl-(R)-3-hydroxybutyrate

The efficient asymmetric bio-synthesis of chiral β-hydroxy esters is of great importance for industrial production. In this work, a simple and productive engineered E.coli cell-immobilized strategy was applied for the asymmetric reduction of MAA to (R)-HBME with high enantioselectivity. Compared with the corresponding inactivated free cells, the alginate-immobilized cells remained 45% of initial activity at 50 ℃ and 65% after reuse of 10 times. After 60 days of storage at 4 ℃, the immobilized cells maintained more than 80% relative activity. Immobilization contributed significantly to the improvement of thermal stability, pH tolerance, storage stability and operation stability without affecting the yield of product. The immobilized recombinant E. coli cell had absolute enantioselectivity for the asymmetric reduction of MAA to (R)-HBME with e.e. > 99.9%. Therefore, microbial cell immobilization is a perspective approach in asymmetric synthesis of chiral β-hydroxy esters for industrial applications.

Designing Sites in Heterogeneous Catalysis: Are We Reaching Selectivities Competitive With Those of Homogeneous Catalysts?

A critical review of different prominent nanotechnologies adapted to catalysis is provided, with focus on how they contribute to the improvement of selectivity in heterogeneous catalysis. Ways to modify catalytic sites range from the use of the reversible or irreversible adsorption of molecular modifiers to the immobilization or tethering of homogeneous catalysts and the development of well-defined catalytic sites on solid surfaces. The latter covers methods for the dispersion of single-atom sites within solid supports as well as the use of complex nanostructures, and it includes the post-modification of materials via processes such as silylation and atomic layer deposition. All these methodologies exhibit both advantages and limitations, but all offer new avenues for the design of catalysts for specific applications. Because of the high cost of most nanotechnologies and the fact that the resulting materials may exhibit limited thermal or chemical stability, they may be best aimed at improving the selective synthesis of high value-added chemicals, to be incorporated in organic synthesis schemes, but other applications are being explored as well to address problems in energy production, for instance, and to design greener chemical processes. The details of each of these approaches are discussed, and representative examples are provided. We conclude with some general remarks on the future of this field.

β-Galactosidase from Kluyveromyces lactis: Characterization, production, immobilization and applications - A review

A review on the enzyme β-galactosidase from Kluyveromyces lactis is presented, from the perspective of its structure and mechanisms of action, the main catalyzed reactions, the key factors influencing its activity, and selectivity, as well as the main techniques used for improving the biocatalyst functionality. Particular attention was given to the discussion of hydrolysis, transglycosylation, and galactosylation reactions, which are commonly mediated by this enzyme. In addition, the products generated from these processes were highlighted. Finally, biocatalyst improvement techniques are also discussed, such as enzyme immobilization and protein engineering. On these topics, the most recent immobilization strategies are presented, emphasizing processes that not only allow the recovery of the biocatalyst but also deliver enzymes that show better resistance to high temperatures, chemicals, and inhibitors. In addition, genetic engineering techniques to improve the catalytic properties of the β-galactosidases were reported. This review gathers information to allow the development of biocatalysts based on the β-galactosidase enzyme from K. lactis, aiming to improve existing bioprocesses or develop new ones.

Application of Rhizomucor miehei lipase-displaying Pichia pastoris whole cell for biodiesel production using agro-industrial residuals as substrate

This work aimed the application of a new biocatalyst for biodiesel production from residual agro-industrial fatty acids. A recombinant Pichia pastoris displaying lipase from Rhizomucor miehei (RML) on the cell surface, using the PIR-1 anchor system, were prepared using glycerol as the carbon source. The biocatalyst, named RML-PIR1 showed optimum temperature of 45 °C (74.0 U/L). The stability tests resulted in t_1/2 of 3.49 and 2.15 h at 40 and 45 °C, respectively. RML-PIR1 was applied in esterification reactions using industrial co-products as substrates, palm fatty acid distillate (PFAD) and soybean fatty acid distillate (SFAD). The highest productivity was observed for SFAD after 48 h presenting 79.1% of conversion using only 10% of biocatalyst and free-solvent system. This is about ca. eight times higher than commercial free RML in the same conditions. The stabilizing agents study revealed that the treatment using glutaraldehyde (GA) and poly(ethylene glycol) (PEG) enabled increased stability and reuse of biocatalyst. It was observed by SEM analysis that the treatment modified the cell morphology. RML-PIR1-GA presented 87.9% of the initial activity after 6 reuses, whilst the activity of unmodified RML-PIR decreased by 40% after the first use. These results were superior to those obtained in the literature, making this new biocatalyst promising for biotechnological applications, such as the production of biofuels on a large scale.

Nanoarray Structures for Artificial Photosynthesis

Conversion and storage of solar energy into fuels and chemicals by artificial photosynthesis has been considered as one of the promising methods to address the global energy crisis. However, it is still far from the practical applications on a large scale. Nanoarray structures that combine the advantages of nanosize and array alignment have demonstrated great potential to improve solar energy conversion efficiency, stability, and selectivity. This article provides a comprehensive review on the utilization of nanoarray structures in artificial photosynthesis of renewable fuels and high value-added chemicals. First, basic principles of solar energy conversion and superiorities of using nanoarray structures in this field are described. Recent research progress on nanoarray structures in both abiotic and abiotic-biotic hybrid systems is then outlined, highlighting contributions to light absorption, charge transport and transfer, and catalytic reactions (including kinetics and selectivity). Finally, conclusions and outlooks on future research directions of nanoarray structures for artificial photosynthesis are presented.

Continuous flow asymmetric synthesis of chiral active pharmaceutical ingredients and their advanced intermediates

Catalytic enantioselective transformations provide well-established and direct access to stereogenic synthons that are broadly distributed among active pharmaceutical ingredients (APIs). These reactions have been demonstrated to benefit considerably from the merits of continuous processing and microreactor technology. Over the past few years, continuous flow enantioselective catalysis has grown into a mature field and has found diverse applications in asymmetric synthesis of pharmaceutically active substances. The present review therefore surveys flow chemistry-based approaches for the synthesis of chiral APIs and their advanced stereogenic intermediates, covering the utilization of biocatalysis, organometallic catalysis and metal-free organocatalysis to introduce asymmetry in continuously operated systems. Single-step processes, interrupted multistep flow syntheses, combined batch/flow processes and uninterrupted one-flow syntheses are discussed herein.

Biophotoelectrochemistry for renewable energy and environmental applications

Biophotoelectrochemistry (BPEC) is an interdisciplinary research field and combines bioelectrochemistry and photoelectrochemistry through the utilization of the catalytic abilities of biomachineries and light harvesters to accomplish the production of energy or chemicals driven by solar energy. The BPEC process may act as a new approach for sustainable green chemistry and waste minimization. This review provides the state-of-the-art introduction of BPEC basics and systems, with a focus on light harvesters and biocatalysts, configurations, photoelectron transfer mechanisms, and the potential applications in energy and environment. Several examples of BPEC applications are discussed including H2 production, CO2 reduction, chemical synthesis, pollution control, and biogeochemical cycle of elements. The challenges about BPEC systems are identified and potential solutions are proposed. The review aims to encourage further research of BPEC toward development of practical BPEC systems for energy and environmental applications.

Solar-Powered Whole-Cell P450 Catalytic Platform for C-Hydroxylation Reactions

Photobiocatalysis is a green platform for driving redox enzymatic reactions using solar energy, not needing high-cost cofactors and redox partners. Here, a visible light-driven whole-cell platform for human cytochrome P450 (CYP) photobiocatalysis was developed using natural flavins as a photosensitizer. Photoexcited flavins mediate NADPH/reductase-free, light-driven biocatalysis by human CYP2E1 both in vitro and in the whole-cell systems. In vitro tests demonstrated that the photobiocatalytic activity of CYP2E1 is dependent on the substrate type, the presence of catalase, and the acid type used as a sacificial electron donor. A protective effect of catalase was found against the inactivation of CYP2E1 heme by H₂ O₂ and the direct transfer of photo-induced electrons to the heme iron not by peroxide shunt. Furthermore, the P450 photobiocatalysis in whole cells containing human CYPs 1A1, 1A2, 1B1, and 3A4 demonstrated the general applicability of the solar-powered, flavin-mediated P450 photobiocatalytic system.

Applications of Ionic Liquids in Whole-Cell and Isolated Enzyme Biocatalysis

Ionic liquids have unique chemical properties that have fascinated scientists in many fields. The effects of adding ionic liquids to biocatalysts are many and varied. The uses of ionic liquids in biocatalysis include improved separations and phase behaviour, reduction in toxicity, and stabilization of protein structures. As the ionic liquid state of the art has progressed, concepts of what can be achieved in biocatalysis using ionic liquids have evolved and more beneficial effects have been discovered. In this review ionic liquids for whole-cell and isolated enzyme biocatalysis will be discussed with an emphasis on the latest developments, and a look to the future.

Photocatalyst-enzyme hybrid systems for light-driven biotransformation

Enzymes catalyse target reactions under mild conditions with high efficiency, as well as excellent regional-, stereo-, and enantiomeric selectivity. Photocatalysis utilises sustainable and environment-friendly light power to realise efficient chemical conversion. By combining the interdisciplinary advantages of photo- and enzymatic catalysis, the photocatalyst-enzyme hybrid systems have proceeded various light-driven biotransformation with high efficiency under environmentally benign conditions, thus, attracting unparalleled focus during the last decades. It has also been regarded as a promising pathway towards green chemistry utilising ubiquitous solar energy. This systematic review gives insight into this research field by classifying the existing photocatalyst-enzyme hybrid systems into three sections based on different hybridizing modes between photo- and enzymatic catalysis. Furthermore, existing challenges and proposed strategies are discussed within this context. The first system summarised is the cofactor-mediated hybrid system, in which natural/artificial cofactors act as reducing equivalents that connect photocatalysts with enzymes for light-driven enzymatic biotransformation. Second, the direct contact-based photocatalyst-enzyme hybrid systems are described, including two different kinds of electron exchange sites on the enzyme molecules. Third, some cases where photocatalysts and enzymes are integrated into a reaction cascade with specific intermediates will be discussed in the following chapter. Finally, we provide perspective concerning the future of this field.

Autodisplay of an endo-1,4-β-xylanase from Clostridium cellulovorans in Escherichia coli for xylans degradation

The goal of this work was the autodisplay of the endo β-1,4-xylanase (XynA) from Clostridium cellulovorans in Escherichia coli using the AIDA system to carry out whole-cell biocatalysis and hydrolysate xylans. For this, pAIDA-xynA vector containing a synthetic xynA gene was fused to the signal peptide of the toxin subunit B Vibro cholere (ctxB) and the auto-transporter of the synthetic aida gene, which encodes for the connector peptide and β-barrel of the auto-transporter (AT-AIDA). E. coli TOP10 cells were transformed and the biocatalyst was characterized using beechwood xylans as substrate. Optimal operational conditions were temperature of 55 °C and pH 6.5, and the Michaelis-Menten catalytic constants V_max and K_m were 149 U/g_DCW and 6.01 mg/mL, respectively. Xylanase activity was inhibited by Cu²⁺, Zn²⁺ and Hg²⁺ as well as EDTA, detergents, and organic acids, and improved by Ca²⁺, Co²⁺ and Mn²⁺ ions. Ca²⁺ ion strongly enhanced the xylanolytic activity up to 2.4-fold when 5 mM CaCl₂ were added. Also, Ca²⁺ improved enzyme stability at 60 and 70 °C. Results suggest that pAIDA-xynA vector has the ability to express functional xylanase to perform whole-cell biocatalysis in order to hydrolysate xylans from hemicellulose feedstock.

Heterologous Expression and Characterization of Flavinadenine Dinucleotide Synthetase from Candida famata for Flavin Adenine Dinucleotide Production

BACKGROUND

Flavin adenine dinucleotide (FAD) is a redox-active coenzyme that regulates several important enzymatic reactions during metabolism. FAD is used in the medicinal and food industries and FAD supplements have been used to treat some inheritable diseases. FAD can be biosynthesized from flavin mononucleotide (FMN) and adenosine triphosphate (ATP), catalyzed by FAD synthetase (FADS).

OBJECTIVE

The aim of this study was to heterologously express the gene encoding FADS from the flavinogenic yeast Candida famata (FADS_Cf) for biosynthesis of FAD.

METHODS

The sequence encoding FADS_Cf was retrieved and heterologously expressed in Escherichia coli. The structure and enzymatic properties of recombinant FADS_Cf were characterized.

RESULTS

FADS_Cf (279 amino acids) was successfully expressed in E. coli BL21 (DE3), with a theoretical molecular weight of 32299.79 Da and an isoelectric point of 6.09. Secondary structural analysis showed that the number of α-helices was 2-fold higher than the number of β-sheets, indicating that the protein was highly hydrophilic. Under fixed ATP concentration, FADS_Cf had a Km of 0.04737±0.03158 mM and a V_max of 3.271±0.79 μM/min/mg. Under fixed FMN concentration, FADSCf had a Km of 0.1214±0.07464 mM and a V_max of 2.6695±0.3715 μM/min/mg. Enzymatic reactions in vitro showed that expressed FADS_Cf could form 80 mM of FAD per mg of enzyme after 21 hours under the following conditions: 0.5 mM FMN, 5 mM ATP and 10 mM Mg²⁺.

CONCLUSION

Under optimized conditions (0.5 mM FMN, 5 mM ATP and 10 mM Mg²⁺), the production of FAD reached 80 mM per mg of FADS_Cf after a 21-hour reaction. Our results indicate that purified recombinant FADS_Cf can be used for the biosynthesis of FAD.

Yeast cell surface display of bacterial PET hydrolase as a sustainable biocatalyst for the degradation of polyethylene terephthalate

Enzymatic hydrolysis of polyethylene terephthalate (PET) is considered to be an environmentally friendly method for the recycling of plastic waste. Recently, a bacterial enzyme named IsPETase was found in Ideonella sakaiensis with the ability to degrade amorphous PET at ambient temperature suggesting its possible use in recycling of PET. However, applying the purified IsPETase in large-scale PET recycling has limitations, i.e., a complicated production process, high cost of single-use, and instability of the enzyme. Yeast cell surface display has proven to be an effectual alternative for improving enzyme degradation efficiency and realizing industrial applications. This chapter deals with the construction and application of a whole-cell biocatalyst by displaying IsPETase on the surface of yeast (Pichia pastoris) cells.

Highly selective synthesis of D-amino acids via stereoinversion of corresponding counterpart by an in vivo cascade cell factory

BACKGROUND

D-Amino acids are increasingly used as building blocks to produce pharmaceuticals and fine chemicals. However, establishing a universal biocatalyst for the general synthesis of D-amino acids from cheap and readily available precursors with few by-products is challenging. In this study, we developed an efficient in vivo biocatalysis system for the synthesis of D-amino acids from L-amino acids by the co-expression of membrane-associated L-amino acid deaminase obtained from Proteus mirabilis (LAAD), meso-diaminopimelate dehydrogenases obtained from Symbiobacterium thermophilum (DAPDH), and formate dehydrogenase obtained from Burkholderia stabilis (FDH), in recombinant Escherichia coli.

RESULTS

To generate the in vivo cascade system, three strategies were evaluated to regulate enzyme expression levels, including single-plasmid co-expression, double-plasmid co-expression, and double-plasmid MBP-fused co-expression. The double-plasmid MBP-fused co-expression strain Escherichia coli pET-21b-MBP-laad/pET-28a-dapdh-fdh, exhibiting high catalytic efficiency, was selected. Under optimal conditions, 75 mg/mL of E. coli pET-21b-MBP-laad/pET-28a-dapdh-fdh whole-cell biocatalyst asymmetrically catalyzed the stereoinversion of 150 mM L-Phe to D-Phe, with quantitative yields of over 99% ee in 24 h, by the addition of 15 mM NADP+ and 300 mM ammonium formate. In addition, the whole-cell biocatalyst was used to successfully stereoinvert a variety of aromatic and aliphatic L-amino acids to their corresponding D-amino acids.

CONCLUSIONS

The newly constructed in vivo cascade biocatalysis system was effective for the highly selective synthesis of D-amino acids via stereoinversion.

Repurposing Inflatable Packaging Pillows as Bioreactors: a Convenient Synthesis of Glucosone by Whole-Cell Catalysis Under Oxygen

Biocatalysis using molecular oxygen as the electron acceptor has significant potential for selective oxidations at low cost. However, oxygen is poorly soluble in water, and its slow rate of mass transfer in the aqueous phase is a major obstacle, even for laboratory-scale syntheses. Oxygen transfer can be accelerated by vigorous mechanical methods, but these are often incompatible with biological catalysts. Gentler conditions can be achieved with shallow, high surface area bag reactors that are designed for single use and generally for specialized cell culture applications. As a less-expensive alternative to these high-end bioreactors, we describe repurposing inflatable shipping pillows with resealable valves to provide high surface area mixing under oxygen for preparative synthesis of glucosone (D-arabino-hexos-2-ulose) from D-glucose using non-growing Escherichia coli whole cells containing recombinant pyranose 2-oxidase (POX) as catalyst. Parallel reactions permitted systematic study of the effects of headspace composition (i.e., air vs 100% oxygen), cell density, exogenous catalase, and reaction volume in the oxidation of 10% glucose. Importantly, only a single charge of 100% oxygen is required for stoichiometric conversion on a multi-gram scale in 18 h with resting cells, and the conversion was successfully repeated with recycled cells.

Selective Biosynthesis of Furoic Acid From Furfural by Pseudomonas Putida and Identification of Molybdate Transporter Involvement in Furfural Oxidation

Upgrading of furanic aldehydes to their corresponding furancarboxylic acids has received considerable interest recently. Herein we reported selective oxidation of furfural (FAL) to furoic acid (FA) with quantitative yield using whole-cells of Pseudomonas putida KT2440. The biocatalytic capacity could be substantially promoted through adding 5-hydroxymethylfurfural into media at the middle exponential growth phase. The reaction pH and cell dosage had notable impacts on both FA titer and selectivity. Based on the validation of key factors for FAL conversion, the capacity of P. putida KT2440 to produce FAL was substantially improved. In batch bioconversion, 170 mM FA was produced with selectivity nearly 100% in 2 h, whereas 204 mM FA was produced with selectivity above 97% in 3 h in fed-batch bioconversion. Particularly, the role of molybdate transporter in oxidation of FAL and 5-hydroxymethylfurfural was demonstrated for the first time. The furancarboxylic acids synthesis was repressed markedly by destroying molybdate transporter, which implied Mo-dependent enzyme/molybdoenzyme played pivotal role in such oxidation reactions. This research further highlights the potential of P. putida KT2440 as next generation industrial workhorse and provides a novel understanding of molybdoenzyme in oxidation of furanic aldehydes.

A review of sustainable lignocellulose biorefining applying (natural) deep eutectic solvents (DESs) for separations, catalysis and enzymatic biotransformation processes

Conventional biorefinery processes are complex, engineered and energy-intensive, where biomass fractionation, a key functional step for the production of biomass-derived chemical substances, demands industrial organic solvents and harsh, environmentally harmful reaction conditions. There is a timely, clear and unmet economic need for a systematic, robust and affordable conversion method technology to become greener, sustainable and cost-effective. In this perspective, deep eutectic solvents (DESs) have been envisaged as the most advanced novel polar liquids that are entirely made of natural, molecular compounds that are capable of an association via hydrogen bonding interactions. DES has quickly emerged in various application functions thanks to a formulations’ simple preparation. These molecules themselves are biobased, renewable, biodegradable and eco-friendly. The present experimental review is providing the state of the art topical overview of trends regarding the employment of DESs in investigated biorefinery-related techniques. This review covers DESs for lignocellulosic component isolation, applications as (co)catalysts and their functionality range in biocatalysis. Furthermore, a special section of the DESs recyclability is included. For DESs to unlock numerous new (reactive) possibilities in future biorefineries, the critical estimation of its complexity in the reaction, separation, or fractionation medium should be addressed more in future studies.

Whole-Cell Biotransformation of 1,12-Dodecanedioic Acid from Coconut Milk Factory Wastewater by Recombinant CYP52A17SS Expressing Saccharomyces cerevisiae

Biotransformation of fatty acids from renewable wastewater as feedstock to value-added chemicals is a fascinating commercial opportunity. α,ω-Dicarboxylic acids (DCAs) are building blocks in many industries, such as polymers, cosmetic intermediates, and pharmaceuticals, and can be obtained by chemical synthesis under extreme conditions. However, biological synthesis can replace the traditional chemical synthesis using cytochrome P450 enzymes to oxidize fatty acids to DCAs. Saccharomyces cerevisiae BY(2R)/pYeDP60-CYP52A17SS (BCM), a transgenic strain expressing the galactose-inducible CYP52A17SS cytochrome P450 enzyme, was able to grow in a coconut milk factory wastewater (CCW) medium and produced 12-hydroxydodecanoic acid (HDDA) and 1,12-dodecanedioic acid (DDA). The supplementation of CCW with 10 g/L yeast extract and 20 g/L peptone (YPCCW) markedly increased the yeast growth rate and the yields of 12-HDDA and 1,12-DDA, with the highest levels of approximately 60 and 38 µg/L, respectively, obtained at 30 °C and pH 5. The incubation temperature and medium pH strongly influenced the yeast growth and 1,12-DDA yield, with the highest 1,12-DDA formation at 30 °C and pH 5–5.5. Hence, the S. cerevisiae BCM strain can potentially be used for producing value-added products from CCW.

Immobilization of the Highly Active UDP-Glucose Pyrophosphorylase From Thermocrispum agreste Provides a Highly Efficient Biocatalyst for the Production of UDP-Glucose

Biocatalysis that produces economically interesting compounds can be carried out by using free enzymes or microbial cells. However, often the cell metabolism does not allow the overproduction or secretion of activated sugars and thus downstream processing of these sugars is complicated. Here enzyme immobilization comes into focus in order to stabilize the enzyme as well as to make the overall process economically feasible. Besides a robust immobilization method, a highly active and stable enzyme is needed to efficiently produce the product of choice. Herein, we report on the identification, gene expression, biochemical characterization as well as immobilization of the uridine-5′-diphosphate-glucose (UDP-glucose) pyrophosphorylase originating from the thermostable soil actinobacterium Thermocrispum agreste DSM 44070 (TaGalU). The enzyme immobilization was performed on organically modified mesostructured cellular foams (MCF) via epoxy and amino group to provide a stable and active biocatalyst. The soluble and highly active TaGalU revealed a V_max of 1698 U mg^–1 (uridine-5′-triphosphate, UTP) and a K_m of 0.15 mM (UTP). The optimum reaction temperature was determined to be 50°C. TaGalU was stable at this temperature for up to 30 min with a maximum loss of activity of 65%. Interestingly, immobilized TaGalU was stable at 50°C for at least 120 min without a significant loss of activity, which makes this enzyme an interesting biocatalyst for the production of UDP-glucose.