Immobilization of Escherichia coli novablue γ-glutamyltranspeptidase in Ca-alginate-k-carrageenan beads

Efficient expression of γ-glutamyl transpeptidase in Bacillus subtilis via CRISPR/Cas9n and its immobilization

In this study, we successfully applied the strategy of combining tandem promoters and tandem signal peptides with overexpressing signal peptidase to efficiently express and produce γ-glutamyl peptidase (GGT) enzymes (BsGGT, BaGGT, and BlGGT) from Bacillus subtilis, Bacillus amyloliquefaciens, and Bacillus licheniformis in Bacillus subtilis ATCC6051Δ5. In order to avoid the problem of instability caused by duplicated strong promoters, we assembled tandem promoters of different homologous genes from different species. To achieve resistance marker-free enzyme in the food industry, we first removed the replication origin and corresponding resistance marker of Escherichia coli from the expression vector. The plasmid was then transformed into the B. subtilis host, and the Kan resistance gene in the expression plasmid was directly edited and silenced using the CRISPR/Cas9n-AID base editing system. As a result, a recombinant protein expression carrier without resistance markers was constructed, and the enzyme activity of the BlGGT strain during shake flask fermentation can reach 53.65 U/mL. The recombinant BlGGT was immobilized with epoxy resin and maintained 82.8% enzyme activity after repeated use for 10 times and 87.36% enzyme activity after storage at 4 °C for 2 months. The immobilized BlGGT enzyme was used for the continuous synthesis of theanine with a conversion rate of 65.38%. These results indicated that our approach was a promising solution for improving enzyme production efficiency and achieving safe production of enzyme preparations in the food industry. KEY POINTS: • Efficient expression of recombinant proteins by a combination of dual promoter and dual signal peptide. • Construction of small vectors without resistance markers in B. subtilis using CRISPR/Cas9n-AID editing system. • The process of immobilizing BlGGT with epoxy resin was optimized.

Redesign of γ-glutamyl transpeptidase from Bacillus subtilis for high-level production of L-theanine by cavity topology engineering

L-Theanine is a multifunctional nonprotein amino acid found naturally in tea leaves. It has been developed as a commercial product for a wide range of applications in the food, pharmaceutical, and healthcare industries. However, L-theanine production catalyzed by γ-glutamyl transpeptidase (GGT) is limited by the low catalytic efficiency and specificity of this class of enzymes. Here, we developed a strategy for cavity topology engineering (CTE) based on the cavity geometry of GGT from B. subtilis 168 (CGMCC 1.1390) to obtain an enzyme with high catalytic activity and applied it to the synthesis of L-theanine. Three potential mutation sites, M97, Y418, and V555, were identified using the internal cavity as a probe, and residues G, A, V, F, Y, and Q, which may affect the shape of the cavity, were obtained directly by computer statistical analysis without energy calculations. Finally, 35 mutants were obtained. The optimal mutant Y418F/M97Q showed a 4.8-fold improvement in catalytic activity and a 25.6-fold increase in catalytic efficiency. The recombinant enzyme Y418F/M97Q exhibited a high space-time productivity of 15.4 g L^-1 h^-1 by whole-cell synthesis in a 5 L bioreactor, which was one of the highest concentrations reported so far at 92.4 g L^-1. Overall, this strategy is expected to enhance the enzymatic activity associated with the synthesis of L-theanine and its derivatives.Key points • Cavity topology engineering was used to modify the GGT for L-theanine biocatalysis. • The catalytic efficiency of GGT was increased by 25.6-fold. • Highest productivity of L-theanine reached 15.4 g L ^-1 h^-1 (92.4 g L^-1) in a 5 L bioreactor.

Immobilization of E. coli expressing γ-glutamyltranspeptidase on its surface for γ-glutamyl compound production

An Escherichia coli strain expressing γ-glutamyltranspeptidase on its extracellular surface using the Met1 to Arg232 fragment of YiaT of E. coli as an anchor protein was immobilized with alginate for repeated use. Measurement of γ-glutamyltranspeptidase activity of the immobilized cells was performed repeatedly at pH 8.73 and 37 °C for 10 days using γ-glutamyl-p-nitroanilide in the presence of 100 mM CaCl₂ and 3% NaCl with and without glycylglycine. Even after the 10th day, the enzyme activity did not decrease from the initial levels. The production of γ-glutamylglutamine from glutamine using the immobilized cells was performed repeatedly at pH 10.5 and 37 °C for 10 days in the presence of 250 mM glutamine, 100 mM CaCl₂, and 3% NaCl. Sixty-four % of glutamine was converted to γ-glutamylglutamine in the first cycle. While repeating the production 10 times, the surface of the beads gradually became covered with white precipitate, and the conversion efficiency gradually decreased, but 72% of the initial value still remained even at the 10th measurement.

First Example of the Extracellular Surface Expression of Intrinsically Periplasmic Escherichia coli γ-Glutamyltranspeptidase, a Member of the N-Terminal Nucleophile Hydrolase Superfamily, and the Use of Cells as a Catalyst for γ-Glutamylvalylglycine Production

Although the purified Escherichia coli γ-glutamyltranspeptidase has much higher transpeptidation activity than hydrolysis activity, almost all γ-glutamyltranspeptidase activity is hydrolysis activity in vivo, that is when measured using the whole cells. By using the Met1 to Arg232 fragment of E. coli YiaT or the CapA of Bacillus subtilis subsp. Natto as an anchor protein, we succeeded in expressing E. coli γ-glutamyltranspeptidase on the extracellular surface of the cells, and these cells showed higher transpeptidation activity than hydrolysis activity in the presence of NaCl. Furthermore, E. coli cells overexpressing γ-glutamyltranspeptidase without an anchor from the T5 promoter maintained γ-glutamyltranspeptidase on the extracellular surface of the cells immediately after being harvested from the culture medium, but the enzyme was released from the extracellular surface of the cells subsequently in the absence of NaCl. Using these cells expressing γ-glutamyltranspeptidase on the extracellular surface, γ-Glu-Val-Gly, a kokumi compound, was successfully produced.

Bacterial Gamma-Glutamyl Transpeptidase, an Emerging Biocatalyst: Insights Into Structure-Function Relationship and Its Biotechnological Applications

Gamma-glutamyl transpeptidase (GGT) enzyme is ubiquitously present in all life forms and plays a variety of roles in diverse organisms. Higher eukaryotes mainly utilize GGT for glutathione degradation, and mammalian GGTs have implications in many physiological disorders also. GGTs from unicellular prokaryotes serve different physiological functions in Gram-positive and Gram-negative bacteria. In the present review, the physiological significance of bacterial GGTs has been discussed categorizing GGTs from Gram-negative bacteria like Escherichia coli as glutathione degraders and from pathogenic species like Helicobacter pylori as virulence factors. Gram-positive bacilli, however, are considered separately as poly-γ-glutamic acid (PGA) degraders. The structure-function relationship of the GGT is also discussed mainly focusing on the crystallization of bacterial GGTs along with functional characterization of conserved regions by site-directed mutagenesis that unravels molecular aspects of autoprocessing and catalysis. Only a few crystal structures have been deciphered so far. Further, different reports on heterologous expression of bacterial GGTs in E. coli and Bacillus subtilis as hosts have been presented in a table pointing toward the lack of fermentation studies for large-scale production. Physicochemical properties of bacterial GGTs have also been described, followed by a detailed discussion on various applications of bacterial GGTs in different biotechnological sectors. This review emphasizes the potential of bacterial GGTs as an industrial biocatalyst relevant to the current switch toward green chemistry.

From Tea Leaves to Factories: A Review of Research Progress in l-Theanine Biosynthesis and Production

l-Theanine is the most popular nonprotein amino acid contained in tea leaves. It is one of the umami components of green tea, contributing to the unique flavor of tea. Because of its various health functions, l-theanine has been commercially developed as a valuable ingredient easily used for various applications in food and pharmaceutical industries. Nowadays, l-theanine is mass-produced by plant extraction, chemical synthesis, or enzymatic transformation in factories. This review embodies the available up to date information on the l-theanine synthesis metabolism in the tea plant as well as approaches to produce it, placing emphasis on the biotransformation of l-theanine. It also gives insight into the challenges of l-theanine production on a large scale, as well as directions for future research. This review comprehensively summarizes information on l-theanine to provide an approach for an in-depth study of l-theanine production.

Alginate/κ-Carrageenan-Based Edible Films Incorporated with Clove Essential Oil: Physico-Chemical Characterization and Antioxidant-Antimicrobial Activity

This study aimed to enhance the properties of CaCl₂ crosslinked sodium alginate/k-carrageenan (SA/KC) incorporated with clove essential oil (CEO). An evaluation of the modification effects on physicochemical, morphological, antioxidant, and antibacterial properties was performed. The properties were observed at various SA/KC ratios (10/0 to 1.5/1), CEO (1.5% to 3%), and CaCl₂ (0% to 2%). The surface morphology was improved by addition of KC and CaCl₂. The Fourier transform infrared (FTIR) result showed insignificant alteration of film chemical structure. The X-ray diffraction (XRD) result confirmed the increased crystallinity index of the film by CaCl₂ addition. On physicochemical properties, a higher proportion of SA/KC showed the declined tensile strength, meanwhile both elongation at break and water solubility were increased. The incorporated CEO film reduced both tensile strength and water solubility; however, the elongation at break was significantly increased. The presence of Ca²⁺ ions remarkably increased the tensile strength despite decreased water solubility. Overall, the addition of KC and CaCl₂ helped in repairing the mechanical properties and flexibility. CEO incorporation showed the effectiveness of profiling the antioxidant and antimicrobial activity indicated by high 2,2-diphenyl-1-picrylhydrazyl (DPPH) scavenging activity up to 90.32% and inhibition zone of E. coli growth up to 113.14 mm².

Tertiary treatment (Chlorella sp.) of a mixed effluent from two secondary treatments (immobilized recombinant P. pastori and rPOXA 1B concentrate) of coloured laboratory wastewater (CLWW)

Industrial development has increased wastewater (WW) volume; generating contamination and disturbing ecosystems, because of breeching disposal parameters. In this work, Coloured Laboratory Wastewater (CLWW), (1500.00 colour units, CU) was separately submitted to two secondary treatments. For the first one CLWW was treated for three cycles C1, C2 and C3 with P. pastoris X33/pGAPZαA-LaccPost-Stop producing rPOXA 1B laccase, immobilized in calcium alginate beads. For the second-one, rPOXA 1B enzyme concentrate was used (three processes: P1, P2, and P3). Both treatments were carried out in a 15 L reactor with 10 L effective work volume (EWV) with 72 h hydraulic retention time. C1, C2, and C3 effluents were flocculated and filtered through quartzite sand, while P1, P2, and P3 effluents were only filtered through quartzite sand. The mixture of secondary effluents was submitted to a tertiary treatment with Chlorella sp. For C1, C2, C3, P1, P2, and P3, CU removal was of 99.16, 99.58, 99.53, 96.72, 97.05 and 96.47%, respectively. Discharge parameters, total organic carbon (TOC), inorganic carbon (IC), chemical oxygen demand (COD) and biological oxygen demand (BOD₅) decreased, although they reached different final values. After the tertiary treatment (144 h) effluent discharge parameters were reduced to 34 ± 4 CU, TOC to 6.6 ± 0.9 mg L^-1 and COD to 155 ± 4 mg L^-1. It was demonstrated that secondary treatments (immobilized recombined cells or recombinant enzyme concentrate) combined with Chlorella sp., (tertiary treatment) attained a considerable removal of discharge parameters, demonstrating a promissory alternative for CLWW sequential treatment.

Immobilization of invertase in calcium alginate and calcium alginate-kappa-carrageenan beads and its application in bioethanol production

Invertase from Saccharomyces cerevisiae was entrapped in Ca-alginate and Ca-alginate-kappa-carrageenan matrix. Optimum pH for the free and immobilized invertase was found to be 4.5 and 5.5, respectively. The optimum hydrolysis temperature was 55 °C for both the free and immobilized forms. K_m values for free invertase and invertase entrapped in Ca-alginate and Ca-alginate-kappa-carrageenan beads were 15, 21, and 19 mM, respectively. Values of V_max for free invertase and invertase entrapped in Ca-alginate and Ca-alginate-kappa-carrageenan beads were 238, 186, and 197 mM min^-1, respectively. Invertase entrapped in Ca-alginate-kappa-carrageenan matrix had the highest pH and thermal stability, higher reusability with 71% retention in activity after nine batches of reuse and higher storage stability with 86% activity retention after 12 weeks at 4 °C, pH 4.5. Fermentation of cane molasses by yeast for bioethanol formation in the presence of free invertase at 30 °C, pH 5.0, led to an increase in ethanol production by 3%. However, the production increased by 9% when invertase entrapped in Ca-alginate-kappa-carrageenan was used as a catalyst.HighlightsInvertase from Saccharomyces cerevisiae was entrapped in Ca-alginate beads.For efficient encapsulation of invertase, kappa-carrageenan was used in combination with alginate as a matrix.Entrapment in Ca-alginate-kappa-carrageenan increased pH and thermal stability of invertase.Invertase entrapped in Ca-alginate-kappa-carrageenan was used for bioethanol production from cane molasses.

Whole Cell Entrapment Techniques

Microbial whole cells are efficient, ecological, and low-cost catalysts that have been successfully applied in the pharmaceutical, environmental, and alimentary industries, among others.Microorganism immobilization is a good way to carry out the bioprocess under preparative conditions. The main advantages of this methodology lie in their high operational stability, easy upstream separation, and bioprocess scale-up feasibility.Cell entrapment is the most widely used technique for whole cell immobilization. This technique-in which the cells are included within a rigid network-is porous enough to allow the diffusion of substrates and products, protects the selected microorganism from the reaction medium, and has high immobilization efficiency (100% in most cases).

l-Theanine: An astounding sui generis integrant in tea

l-theanine (l-Th), a non-protein amino acid present in tea, is a valuable nutraceutical product with unique health benefits and used as an additive in food industry. l-Th enhances the umami taste but its use is limited due to its inadequate production. Different extraction approaches from tea shoots, chemical synthesis to microbial transformation have been tried to meet its demand. In vitro, in vivo as well as clinical studies have shown its positive effect in regulating CNS disorders. l-Th has become choice ingredient in CNS active products due to its anti-stress and neuroprotective role in dementias particularly in retrogression of Alzheimer's. l-Th biochemically modulates various anti-neoplastic agents by increasing their bioavailability in tumour cells. The review, is an effort to condense the recent research on l-Th highlighting its biological resource, plausible role in tea plant, production approaches, its physiological role on human health and future prospects.

Carboxymethyl starch/alginate microspheres containing diamine oxidase for intestinal targeting

The association of carboxymethyl starch (CMS) and alginate is proposed as a novel matrix for the entrapment of bioactive agents in microspheres affording their protection against gastrointestinal degradation. In this study, the enzyme diamine oxidase (DAO) from white pea (Lathyrus sativus) was immobilized by inclusion in microspheres formed by ionotropic gelation of CMS/alginate by complexation with Ca(2+) . The association of CMS to alginate generated a more compact structure presenting a lesser porosity, thus decreasing the access of gastric fluid inside the microspheres and preventing the loss of entrapped enzyme. Moreover, the immobilized enzyme remained active and was able to oxidize the polyamine substrates even in the presence of degrading proteases of pancreatin. The inclusion yield in terms of entrapped protein was of about 82%-95%. The DAO entrapped in calcium CMS/alginate beads retained up to 70% of its initial activity in simulated gastric fluid (pH 2.0). In simulated intestinal fluid (pH 7.2) with pancreatin, an overall retention of 65% of activity for the immobilized DAO was observed over 24 H, whereas in similar conditions the free enzyme was totally inactivated. Our project proposes the vegetal DAO as an antihistaminic agent orally administered to treat food histaminosis and colon inflammation.

Whole cell entrapment techniques

Microbial whole cells are efficient, ecological, and low-cost catalysts that have been successfully applied in the pharmaceutical, environmental, and alimentary industries, among others. Microorganism immobilization is a good way to carry out the bioprocess under preparative conditions. The main advantages of this methodology lie in their high operational stability, easy upstream separation and bioprocess scale-up feasibility. Cell entrapment is the most widely used technique for whole cell immobilization. This technique-in which the cells are included within a rigid network-is porous enough to allow the diffusion of substrates and products, protects the selected microorganism from the reaction medium, and has high immobilization efficiency (100 % in most cases).

Characterization and immobilization of purified Aspergillus flavipesl-methioninase: continuous production of methanethiol

AIMS

To immobilize the purified Aspergillus flavipesl-methioninase on solid carriers for continuous production of methanethiol with high purity, by the enzymatic methods.

METHODS AND RESULTS

The purified l-methioninase was immobilized using different methods, and physicochemical and kinetic studies for the potent immobilized enzyme were conducted parallel to the soluble one. The activity of the purified extracellular enzyme was 1·8-fold higher than intracellular one from submerged cultures of A. flavipes. Among the tested methods, polyacrylamide (42·2%), Ca-alginate (40·9%) and chitin (40·8%) displayed the highest immobilization efficiency. The thermal inactivation rate was strongly decreased for chitin-immobilized enzyme (0·222 s⁻¹) comparing to soluble enzyme (0·51 s⁻¹). Enzyme immobilization efficiency was greatly improved using 4·0% glutaraldehyde and 41·6/6·3 (T/C) as spacers for chitin and polyacrylamide-enzyme conjugates, comparing to their controls. Also the incorporation of lysine, glutathione, cysteine and dithiothreitol as active site protectants significantly enhance the catalytic efficiency of immobilized enzyme. The activity of enzyme was increased by 4·5- and 3·5-fold using glutathione plus DDT and glutathione plus methionine, for chitin and polyacrylamide enzyme, respectively.

CONCLUSION

Chitin enzyme gave a plausible stability till fourth cycle for production of methanethiol under controlled system. Applying GC and HNMR analysis, methanethiol has identical chemical structure to the standard compound.

SIGNIFICANCE AND IMPACT OF THE STUDY

Technically, a new method for continuous production of pure methanethiol, with broad applications, was developed using a simple low expenses method.

Alginate immobilization of recombinant Escherichia coli whole cells harboring L-arabinose isomerase for L-ribulose production

Recombinant Escherichia coli whole cells harboring Bacillus licheniformis L-arabinose isomerase (BLAI) were immobilized with alginate. The operational conditions for immobilization were optimized with response surface methodology. Optimal alginate concentration, Ca(2+) concentration, and cell mass loading were 1.8% (w/v), 0.1 M, and 44.5 g L(-1), respectively. The interactions between Ca(2+) concentration, alginate concentration, and initial cell mass were significant. After immobilization of BLAI, cross-linking with 0.1% glutaraldehyde significantly reduced cell leakage. The half-life of immobilized whole cells was 150 days, which was 50-fold longer than that of free cells. In seven repeated batches for L-ribulose production, the productivity was as high as 56.7 g L(-1) h(-1) at 400 g L(-1) substrate concentration. The immobilized cells retained 89% of the initial yield after 33 days of reaction. Immobilization of whole cells harboring BLAI, therefore, makes a suitable biocatalyst for the production of L-ribulose, particularly because of its high stability and low cost.