Enhanced glucosamine production by Aspergillus sp. BCRC 31742 based on the time-variant kinetics analysis of dissolved oxygen level

An update on the review of microbial synthesis of glucosamine and N-acetylglucosamine

Glucosamine (GlcN) is a natural amino monosaccharide in which a hydroxyl group of glucose is substituted by an amino group. It belongs to functional amino sugar compounds. In the traditional preparation process, GlcN and GlcNAc are obtained by hydrolyzing the cell wall of shrimp and crab. There are many potential problems with this method, such as geographical and seasonal restrictions on the supply of raw materials, serious environmental pollution and potential allergic reactions. Microbial fermentation has the advantages of mild conditions, low environmental pollution, high production intensity, and product safety. It can effectively solve the problem of shrimp and crab hydrolysis process, attracting many researchers to participate in the research of microbial fermentation production of GlcN. This paper mainly summarizes the research on strain construction method, metabolic pathway design and fermentation condition optimization in microbial fermentation, which has certain guiding significance for the further production, research and production of glucosamine.

Multifaceted production strategies and applications of glucosamine: a comprehensive review

Glucosamine (GlcN) and its derivatives are in high demand and used in various applications such as food, a precursor for the biochemical synthesis of fuels and chemicals, drug delivery, cosmetics, and supplements. The vast number of applications attributed to GlcN has raised its demand, and there is a growing emphasis on developing production methods that are sustainable and economical. Several: physical, chemical, enzymatic, microbial fermentation, recombinant processing methods, and their combinations have been reported to produce GlcN from chitin and chitosan available from different sources, such as animals, plants, and fungi. In addition, genetic manipulation of certain organisms has significantly improved the quality and yield of GlcN compared to conventional processing methods. This review will summarize the chitin and chitosan-degrading enzymes found in various organisms and the expression systems that are widely used to produce GlcN. Furthermore, new developments and methods, including genetic and metabolic engineering of Escherichia coli and Bacillus subtilis to produce high titers of GlcN and GlcNAc will be reviewed. Moreover, other sources of glucosamine production viz. starch and inorganic ammonia will also be discussed. Finally, the conversion of GlcN to fuels and chemicals using catalytic and biochemical conversion will be discussed.

Mycofabrication of Mycelium-Based Leather from Brown-Rot Fungi

Sustainable substitutes for leather can be made from mushroom mycelium, which is an environmentally friendly alternative to animal and synthetic leather. Mycelium-based leather is derived from Polyporales, in which lignocellulosic material is used as the substrate. The plasticizing and crosslinking of mycelial mats with various reagents might affect the leather properties and mycelial architecture. This study investigated the physicochemical and mechanical properties of mycelium-based leather (MBL) samples, including the hygroscopic nature, thermal stability, cell wall chemistry, density, micromorphology, tensile strength, elongation rate, and Young’s modulus. Micromorphological observations confirmed the mycelial networks and their binding performance, verifying their efficacy as a substitute leather. The most significant effects were observed after treatment with 20% polyethylene glycol, which resulted in an increase in Young’s modulus and tensile strength. Furthermore, the samples generally exhibited a high density (1.35, 1.46 g/cm³) and tensile strength (7.21 ± 0.93, 8.49 ± 0.90 MPa), resembling leather. The tear strength reached as low as 0.5–0.8 N/mm. However, the tensile and tear strength may be affected by leather processing and the tuning of mycelial growth. Nevertheless, high-density mycelia are shown to be suitable for the production of MBL, while mycofabrication and strain selection are sustainable for novel industrial applications of MBL.

Engineering diacetylchitobiose deacetylase from Pyrococcus horikoshii towards an efficient glucosamine production

In this study, semi-rational design based on site-directed saturation mutagenesis and surface charge modification was used to improve the catalytic efficiency of the diacetylchitobiose deacetylase derived from Pyrococcus horikoshii (PhDac). PhDac mutant M14, which was screened by site-directed saturation mutagenesis, showed a ~ 2.21 -fold enhanced catalytic efficiency (kcat/Km) and the specific activity was improved by 70.02%. To keep the stability of glucosamine (GlcN), we reduced the optimal pH of M14 by modifying the surface charge from -35 to -59 to obtain mutant M20, whose specific activity reached 2 -fold of the wild-type. The conversion rate of N-acetylglucosamine (GlcNAc) to GlcN catalyzed by M20 reached 94.3%. Moreover, the decline of GlcN production was slowed down by the reduction of pH when temperature was higher than 50 ℃. Our results would accelerate the process of industrial production of GlcN by biocatalysis.

Enhancing ectoine production by recombinant Escherichia coli through step-wise fermentation optimization strategy based on kinetic analysis

In this study, the recombinant ectoine-producing Escherichia coli ET01 was constructed by introducing the ectABC operon from Halomonas venusta ZH. To further improve ectoine production, the regulation of the fermentation process was systematically investigated. First, the effects of the initial glucose concentrations and glucose feeding mode on ectoine production were analyzed. Using a combination of pH-feedback feeding and glucose-controlled feeding, the ectoine titer reached 25.5 g/L, representing an 8.8-fold increase over standard batch culture. Then, the effects of dissolved oxygen (DO) levels (50, 40, 30, or 20%) on ectoine production were studied, and a DO control strategy was developed based on the fermentation kinetics. When the final optimized two-stage fermentation strategy was used, the ectoine titer reached 47.8 g/L, which was the highest level of ectoine produced by E. coli fermentation. The fermentation regulation strategy developed in this study might be useful for scaling up the commercial production of ectoine.

Process optimization and scale-up production of fungal aryl alcohol oxidase from genetically modified Aspergillus nidulans in stirred-tank bioreactor

Microbial production of aryl alcohol oxidase (AAO) has attracted increasing attention due to the central role of AAO in enzymatic lignin depolymerization. However, large-scale production of AAO has not been reached because of the low yield and inefficient fermentation process. This study aims to optimize the process parameters and scale-up production of AAO using Aspergillus nidulans in a stirred-tank bioreactor. Effects of pH and dissolved oxygen on AAO production at bioreactor scale were particularly investigated. Results revealed that pH control significantly affected protein production and increasing dissolved oxygen level stimulated AAO production. The greatest AAO activity (1906 U/L) and protein concentration (1.19 g/L) were achieved in 48 h at 60% dissolved oxygen with pH controlled at 6.0. The yield and productivity (in 48 h) were 31.2 U/g maltose and 39.7 U/L/h, respectively. In addition, crude AAO was concentrated and partially purified by ultrafiltration and verified by protein identification.

Metabolic engineering of Corynebacterium glutamicum S9114 based on whole-genome sequencing for efficient N-acetylglucosamine synthesis

Glucosamine (GlcN) and its acetylated derivative N-acetylglucosamine (GlcNAc) are widely used in the pharmaceutical industries. Here, we attempted to achieve efficient production of GlcNAc via genomic engineering of Corynebacterium glutamicum. Specifically, we ligated the GNA1 gene, which converts GlcN-6-phosphate to GlcNAc-6-phosphate by transferring the acetyl group in Acetyl-CoA to the amino group of GlcN-6-phosphate, into the plasmid pJYW4 and then transformed this recombinant vector into the C. glutamicum ATCC 13032, ATCC 13869, ATCC 14067, and S9114 strains, and we assessed the GlcNAc titers at 0.5 g/L, 1.2 g/L, 0.8 g/L, and 3.1 g/L from each strain, respectively. This suggested that there were likely to be significant differences among the key genes in the glutamate and GlcNAc synthesis pathways of these C. glutamicum strains. Therefore, we performed whole genome sequencing of the S9114 strain, which has not been previously published, and found that there are many differences among the genes in the glutamate and GlcNAc synthesis pathways among the four strains tested. Next, nagA (encoding GlcNAc-6-phosphate deacetylase) and gamA (encoding GlcN-6-phosphate deaminase) were deleted in C. glutamicum S9114 to block the catabolism of intracellular GlcNAc, leading to a 54.8% increase in GlcNAc production (from 3.1 to 4.8 g/L) when grown in a shaker flask. In addition, lactate synthesis was blocked by knockout of ldh (encoding lactate dehydrogenase); thus, further increasing the GlcNAc titer to 5.4 g/L. Finally, we added a key gene of the GlcN synthetic pathway, glmS, from different sources into the expression vector pJYW-4-ceN, and the resulting recombinant strain CGGN2-GNA1-CgglmS produced the GlcNAc titer of 6.9 g/L. This is the first report concerning the metabolic engineering of C. glutamicum, and the results of this study provide a good starting point for further metabolic engineering to achieve industrial-scale production of GlcNAc.

Critical evaluation of a putative glucosamine excretion by Aspergillus niger CBS120.49 and Penicillium ochrochloron CBS123.824 under citric acid producing conditions

As one of the most frequently occurring monomers in the biosphere, glucosamine is a valuable metabolite for several applications. Although microbial glucosamine production is still in its infancy, it offers the possibility to circumvent problems associated with traditional production by hydrolysis. Of particular interest is a study with Aspergillus niger, which reports for the first time high glucosamine excretion in the early phase of citric acid production. These results have relevance for both the commercial glucosamine production and deeper insight into the regulation of organic acid excretion in fungi. To investigate glucosamine excretion, we performed bioreactor batch cultivations with Penicillium ochrochloron CBS123.824 and A. niger CBS120.49 using cultivation conditions which are known to trigger the production of citric acid. Glucosamine detection in culture filtrates was achieved by two photometric methods, High performance liquid chromatography with evaporative light scattering detection (HPLC-ELSD) and HPLC with mass spectrometry detection (HPLC-MS). Surprisingly, we detected no glucosamine at all. Based on a critical review of published data for A. niger, we conclude that the reported high levels of excreted glucosamine might be an experimental artifact. However, growth experiments with glucosamine as a combined or single source for carbon or nitrogen showed that both organisms are in principle able to transport glucosamine across their plasma membrane, which is a prerequisite for the excretion of glucosamine.

Study on feasibility of determination of glucosamine content of fermentation process using a micro NIR spectrometer

N-acetyl-d-glucosamine (GlcNAc) is a microbial fermentation product, and NIR spectroscopy is an effective process analytical technology (PAT) tool in detecting the key quality attribute: the GlcNAc content. Meanwhile, the design of NIR spectrometers is under the trend of miniaturization, portability and low-cost nowadays. The aim of this study was to explore a portable micro NIR spectrometer with the fermentation process. First, FT-NIR spectrometer and Micro-NIR 1700 spectrometer were compared with simulated fermentation process solutions. The R_c², R_p², RMSECV and RMSEP of the optimal FT-NIR and Micro-NIR 1700 models were 0.999, 0.999, 3.226 g/L, 1.388 g/L and 0.999, 0.999, 1.821 g/L, 0.967 g/L. Passing-Bablok regression method and paired t-test results showed there were no significant differences between the two instruments. Then the Micro-NIR 1700 was selected for the practical fermentation process, 135 samples from 10 batches were collected. Spectral pretreatment methods and variables selection methods (BiPLS, FiPLS, MWPLS and CARS-PLS) for PLS modeling were discussed. The R_c², R_p², RMSECV and RMSEP of the optimal GlcNAc content PLS model of the practical fermentation process were 0.994, 0.995, 2.792 g/L and 1.946 g/L. The results have a positive reference for application of the Micro-NIR spectrometer. To some extent, it could provide theoretical supports in guiding the microbial fermentation or the further assessment of bioprocess.

Programming a Biofilm-Mediated Multienzyme-Assembly-Cascade System for the Biocatalytic Production of Glucosamine from Chitin

Chitin is used as an essential raw material for the production of glucosamine (GlcN). In this study, we adopted three key enzymes, isolated from Thermococcus kodakaraensis KOD1, that catalyze the sequential conversion of α-chitin into GlcN and developed a multienzyme-assembly-cascade (MAC) system immobilized in a bacterial biofilm, which enabled a multistep one-pot reaction. Specifically, the SpyTag-SpyCatcher and SnoopTag-SnoopCatcher pairs provided covalent and specific binding force to fix enzymes to the biofilm one by one and assemble close enzyme cascades. The MAC system showed great catalytic activity, converting 79.02 ± 3.61% of α-chitin into GlcN with little byproducts, which was 2.09 times that of GlcN catalyzed by a mixture of pure enzymes. The system also exhibited good temperature and pH stability. Notably, 90% of enzyme activity was retained after 6 rounds of reuse, and appreciable activity remained after 17 rounds.

Combinatorial promoter engineering of glucokinase and phosphoglucoisomerase for improved N-acetylglucosamine production in Bacillus subtilis

In previous work, a recombinant Bacillus subtilis strain was successfully constructed for microbial production of N-acetylglucosamine (GlcNAc). In this study, GlcNAc titer was further improved by combinatorial promoter engineering of key genes glck encoding glucokinase and pgi encoding phosphoglucoisomerase. First, three promoters including constitutive promoter P₄₃, xylose inducible promoter P_xylA, and isopropyl-β-d-thiogalactoside inducible P_grac were used to replace the native promoters of glcK and pgi, yielding 12 recombinant strains. It was found that when glcK and pgi were both under the control of promoter P_xylA, the highest GlcNAc titer in 3-L fed-batch bioreactor reached 35.12g/L, which was 52.6% higher than that of the initial host. Next, the transcriptional levels of the related genes in glycolysis, GlcNAc synthesis pathway, peptidoglycan synthesis pathway, and pentose phosphate pathway were investigated by quantitative real-time PCR analysis. Fine-tuning upper GlcNAc synthesis pathway by combinatorial promoter substitution significantly enhanced GlcNAc production in engineered B. subtilis.

Isolation and characterization of Sphingomonas sp. Y2 capable of high-efficiency degradation of nonylphenol polyethoxylates in wastewater

Nonylphenol polyethoxylates (NPEOs), although banned for decades, are still widely used in manufactories and thus affect human lives. In this study, a highly efficient NPEO-degrading bacterium, Sphingomonas sp. Y2, was isolated from sewage sludge by enrichment culture. Strain Y2 ensured the complete removal of NPEO in 48 h and degraded 99.2 % NPEO (1,000 mg L(-1)) within 30 h at a specific growth rate of 0.73 h(-1) in minimum salt medium. To date, this degradation efficiency is the highest reported for NPEO metabolism by a pure bacterium under this condition. Furthermore, the application of this bacterium to wastewater treatment demonstrated that it metabolized 98.5 % NPEO (1,000 mg L(-1)) within 5 days with a specific growth rate of 2.03 day(-1). The degradation intermediates, identified as nonylphenol, short-chain NPEOs and short-chain nonylphenol polyethoxycarboxylates by high-performance liquid chromatography and gas chromatography-mass spectrometry, indicated the sequential exo-cleavage of the EO chain. Additionally, the enzymes involved in the biodegradation were inducible rather than constitutive. Considering that strain Y2 exhibits prominent biodegradation advantages in industrial wastewater treatment, it might serve as a promising potential candidate for in situ bioremediation of contamination by NPEOs and other structurally similar compounds.

An optimal glucose feeding strategy integrated with step-wise regulation of the dissolved oxygen level improves N-acetylglucosamine production in recombinant Bacillus subtilis

In our previous work, a recombinant Bacillus subtilis strain for the microbial production of N-acetylglucosamine (GlcNAc) was constructed through modular pathway engineering. In this study, to enhance GlcNAc production, glucose feeding approaches and dissolved oxygen (DO) control methods in fed-batch culture were systematically investigated. We first studied the effects of different glucose feeding strategies, including exponential fed-batch culture, pulse fed-batch culture, constant rate fed-batch culture, and glucose control (5 g/L, 10 g/L, 15 g/L) fed-batch culture, on cell growth and GlcNAc synthesis. We found that GlcNAc production in glucose control (5 g/L) fed-batch culture reached 26.58 g/L, which was 3.10 times that in batch culture. Next, the effect of DO level (20%, 30%, 40%, and 50%) on GlcNAc production was investigated, and a step-wise DO control strategy (0-7 h, 30%; 7-15 h, 50%; 15-50 h, 40%; 50-72 h, 30%) was introduced. With the optimal glucose and DO control strategy, GlcNAc production reached 35.77 g/L, which was 4.17 times the production in batch culture without DO control.

Enhanced Glucosamine Production with Actinomucor elegans Based on Stimulating Factor of Methanol

Glucosamine (GlcN) is a major and valuable component in the cell wall of fungi. In this study, the cell wall was treated via a two-stage alkali and acid process, and chitin and chitosan were fully deacetylated, partially depolymerized, and converted to GlcN oligosaccharides. Then, the oligosaccharides were analyzed by high performance liquid chromatography. The influences of Actinomucor elegans on GlcN production in a flask culture were investigated to achieve an optimum yield of GlcN. The experimental result showed that cultivation in condition of pH 6.0, 100 mL working volume (500 mL flask), 10 % (v/v) inoculum concentration, at 28 °C and 200 rpm for 6 days yielded highest dry cell weight (DCW) which was 23.43 g L(-1), with a GlcN concentration of 5.12 g L(-1). Methanol as stimulating factor was found to exert the best effect in concentration of 1.5 % (v/v). With addition of methanol into medium, the DCW increased from 23.69 to 32.42 g L(-1), leading to maximum GlcN concentration of 6.85 g L(-1) obtained. Here, the methanol addition may be useful for industrial production of GlcN, and may also be meaningful for the production of other fine chemicals by filamentous fungi.