Hydrogel-Based Enzyme and Cofactor Co-Immobilization for Efficient Continuous Transamination in a Microbioreactor

Cell-free systems: A synthetic biology tool for rapid prototyping in metabolic engineering

Microbial cell factories provide sustainable alternatives to petroleum-based chemical production using cost-effective substrates. A deep understanding of their metabolism is essential to harness their potential along with continuous efforts to improve productivity and yield. However, the construction and evaluation of numerous genetic variants are time-consuming and labor-intensive. Cell-free systems (CFSs) serve as powerful platforms for rapid prototyping of genetic circuits, metabolic pathways, and enzyme functionality. They offer numerous advantages, including minimizing unwanted metabolic interference, precise control of reaction conditions, reduced labor, and shorter Design-Build-Test-Learn cycles. Additionally, the introduction of in vitro compartmentalization strategies in CFSs enables ultra-high-throughput screening in physically separated spaces, which significantly enhances prototyping efficiency. This review highlights the latest examples of using CFS to overcome prototyping limitations in living cells with a focus on rapid prototyping, particularly regarding gene regulation, enzymes, and multienzymatic reactions in bacteria. Finally, this review evaluates CFSs as a versatile prototyping platform and discusses its future applications, emphasizing its potential for producing high-value chemicals through microbial biosynthesis.

Immobilization of His6-tagged amine transaminases in microreactors using functionalized nonwoven nanofiber membranes

Process intensification is crucial for industrial implementation of biocatalysis and can be achieved by continuous process operation in miniaturized reactors with efficiently immobilized biocatalysts, enabling their long-term use. Due to their extremely large surface-to-volume ratio, nanomaterials are promising supports for enzyme immobilization. In this work, different functionalized nanofibrous nonwoven membranes were embedded in a two-plate microreactor to enable immobilization of hexahistidine (His6)-tagged amine transaminases (ATAs) in flow. A membrane coated with Cu2+ ions gave the best results regarding His6-tagged ATAs immobilization among the membranes tested yielding an immobilization yield of up to 95.3 % for the purified N-His6-ATA-wt enzyme. Moreover, an efficient one-step enzyme immobilization process from overproduced enzyme in Escherichia coli cell lysate was developed and yielded enzyme loads up to 1088 U mL-1. High enzyme loads resulted in up to 80 % yields of acetophenone produced from 40 mM (S)-α-methylbenzylamine in less than 4 min using a continuously operated microreactor. Up to 81 % of the initial activity was maintained in a 5-day continuous microreactor operation with immobilized His6-tagged ATA constructs. The highest turnover number within the indicated time was 7.23·106, which indicates that this immobilization approach using advanced material and reactor system is highly relevant for industrial implementation.

Immobilization and characterization of β-galactosidase from Aspergillus oryzae in polyvinyl alcohol hydrogels

One of the main goals of contemporary biotechnology has been the development of novel immobilized enzyme formulations. In the present study, the industrially important β-galactosidase was trapped in a polyvinyl alcohol (PVA) gel to immobilize it. The optimization of immobilization method and characterization of the immobilized enzyme were studied. The results were compared with free enzymes. The results indicate that the optimal temperature range for the enzyme to be at following immobilization is between 40°C and 50°C. At pH 7, the optimal pH, the activity increased, the Vmax value increased from 1.936 to 2.495 U mg‒1, and the Km value decreased from 4.861 to 0.982 mM. Depending on how stable the immobilized enzyme when stored, β-galactosidases immobilized on PVA gels showed 52.87% activity at the end of the seventh week and 58.86% activity at the end of the fifth week. Their initial activity subsided after three reuses. The final result was 66%. Therefore, one may argue that it increases the catalytic effect of the enzyme. As a result, it has been found that immobilized β-galactosidase has more potent enzymatic properties than free β-galactosidase, which may make it more advantageous for industrial processes. Further studies could delve deeper into the mechanistic aspects of the immobilization process in an effort to improve optimization and tailor the immobilized enzyme to specific industrial needs.

Development of a Microbioreactor for Bacillus subtilis Biofilm Cultivation

To improve our understanding of Bacillus subtilis growth and biofilm formation under different environmental conditions, two versions of a microfluidic reactor with two channels separated by a polydimethylsiloxane (PDMS) membrane were developed. The gas phase was introduced into the channel above the membrane, and oxygen transfer from the gas phase through the membrane was assessed by measuring the dissolved oxygen concentration in the liquid phase using a miniaturized optical sensor and oxygen-sensitive nanoparticles. B. subtilis biofilm formation was monitored in the growth channels of the microbioreactors, which were designed in two shapes: one with circular extensions and one without. The volumes of these microbioreactors were (17 ± 4) μL for the reactors without extensions and (28 ± 4) μL for those with extensions. The effect of microbioreactor geometry and aeration on B. subtilis biofilm growth was evaluated by digital image analysis. In both microbioreactor geometries, stable B. subtilis biofilm formation was achieved after 72 h of incubation at a growth medium flow rate of 1 μL/min. The amount of oxygen significantly influenced biofilm formation. When the culture was cultivated with a continuous air supply, biofilm surface coverage and biomass concentration were higher than in cultivations without aeration or with a 100% oxygen supply. The channel geometry with circular extensions did not lead to a higher total biomass in the microbioreactor compared to the geometry without extensions.

Enzymatic Routes for Chiral Amine Synthesis: Protein Engineering and Process Optimization

Chiral amines are essential motifs in pharmaceuticals, agrochemicals, and specialty chemicals. While traditional chemical routes to chiral amines often lack stereoselectivity and require harsh conditions, biocatalytic methods using engineered enzymes can offer high efficiency and selectivity under sustainable conditions. This review discusses recent advances in protein engineering of transaminases, oxidases, and other enzymes to improve catalytic performance. Strategies such as directed evolution, immobilization, and computational redesign have expanded substrate scope and enhanced efficiency. Furthermore, process optimization guided by techno-economic assessments has been crucial for establishing viable biomanufacturing routes. Combining state-of-the-art enzyme engineering with multifaceted process development will enable scalable, economical enzymatic synthesis of diverse chiral amine targets.

Tuning Mechanical Characteristics and Permeability of Alginate Hydrogel by Polyvinyl Alcohol and Deep Eutectic Solvent Addition

Alginate-based hydrogels are widely utilized for various applications, including enzyme immobilization and the development of drug delivery systems, owing to their advantageous characteristics, such as low toxicity, high availability and cost-effectiveness. However, the broad applicability of alginate hydrogels is hindered by their limited mechanical and chemical stability, as well as their poor permeability to hydrophobic molecules. In this study, we addressed the mechanical properties and chemical resistance of alginate hydrogels in a high-pKa environment by the copolymerization of alginate with polyvinyl alcohol (PVA). The addition of PVA resulted in a threefold improvement in the shear modulus of the copolymeric hydrogel, as well as enhanced chemical resistance to (S)-α-methylbenzylamine, a model molecule with a high pKa value. Furthermore, we addressed the permeability challenge by introducing a betaine-propylene glycol deep eutectic solvent (DES) into the PVA-alginate copolymer. This led to an increased permeability for ethyl 3-oxobutanoate, a model molecule used for bioreduction to chiral alcohols. Moreover, the addition of the DES resulted in a notable improvement of the shear modulus of the resulting hydrogel. This dual effect highlights the role of the DES in achieving the desired improvement of the hydrogel as an immobilization carrier.

Enzyme-functionalized hydrogel film for extracorporeal uric acid reduction

Enzyme replacement therapy for hyperuricemia treatment has been proven effective for critical state hyperuricemia patients. Still, direct administration of recombinant uricase can induce several fatal side effects. To circumvent this drawback, hydrogel protein carriers can be used in platforms for extracorporeal treatment such as microscale-based devices. In this work, calcium alginate and poly-(vinyl alcohol) hydrogel films were studied for their urate oxidase immobilization and uric acid reduction, which could be implemented in microscale-based extracorporeal devices. A mathematical model was developed in conjunction with uric acid reduction experiments to evaluate the influence of mass transfer and reaction parameters in the Michaelis-Menten kinetic expression. Alginate hydrogels prepared with crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide and N-(hydroxysuccinimide) offered superior diffusivity of uric acid in the gel matrix at the maximum value ofD g , UA ≈ $$ {D}_{\mathrm{g},\mathrm{UA}}\approx $$ 1.98 × 10-11  m2 /s compared with alginate prepared solely from ionic crosslinking withD g , UA ≈ $$ {D}_{\mathrm{g},\mathrm{UA}}\approx $$  5.31 × 10-12  m2 /s at the same alginate concentration. The maximum value of νmax was experimentally determined at 7.78 × 10-5  mol/(m3 s). A 3% sodium alginate hydrogel with crosslinkers yielded the highest reduction of uric acid at 92.70%. The mathematical model demonstrated an excellent prediction of uric acid conversion suggesting potential use of the model for formulation and maximizing the therapeutic performance of functionalized hydrogels.

Improved biotransformation of lignin-valorized vanillin into vanillylamine in a sustainable bioreaction medium

Lignin is a critical biopolymer for creating a large number of highly valuable biobased compounds. Vanillin, one of lignin-derived aromatics, can be used to synthesize vanillylamine that is a key fine chemical and pharmaceutical intermediate. To produce vanillylamine, a productive whole-cell-catalyzed biotransformation of vanillin was developed in deep eutectic solvent - surfactant - H2O media. One newly created recombinant E. coli 30CA cells expressing ω-transaminase and L-alanine dehydrogenase was employed to transform 50 mM and 60 mM vanillin into vanillylamine in the yield of 82.2% and 8.5% under 40 °C, respectively. The biotransamination efficiency was enhanced by introducing surfactant PEG-2000 (40 mM) and deep eutectic solvent ChCl:LA (5.0 wt%, pH 8.0), and the highest vanillylamine yield reached 90.0% from 60 mM vanillin. Building an effective bioprocess was utilized for transamination of lignin-derived vanillin to vanillylamine with newly created bacteria in an eco-friendly medium, which had potential application for valorization of lignin to value-added compounds.

In situ modulation of enzyme activity via heterogeneous catalysis utilizing solid electroplated cofactors

During product isolation the received bioreceptors often do not exhibit a sufficient biochemical activity due to multistep dissociation and loss of cofactors. However, for bioelectrochemical applications the presence of cofactors is necessary for a successful oxidative or reductive conversion of the substrates to the products. Herein, we show how the immobilization of the required electroplated cofactors in a design of amperometric electrodes can in situ assist the activity of apo-enzymes. Compared to conventional approaches used in enzyme engineering this tailored nanoengineering methodology is superior from economic point of view, labor and time costs, storage conditions, reduced amount of waste and can fill the gap in the development of tuned bioelectrocatalysts.