Enzymatic Modification of Native Chitin and Conversion to Specialty Chemical Products

Immobilized chitinase as effective biocatalytic platform for producing bioactive di-N-acetyl chitobiose from recycled chitin food waste

Described is chitinase immobilization on magnetic nanoparticles (MNPs) as biocompatible support for enzymatic production of di-N-acetyl chitobiose from chitin waste. Chitinase immobilization was feasible with an immobilization yield of 88.9 ± 1.6 % with 97.8 ± 1.0 % retention of activity and compared to free enzyme work, immobilization conferred better thermal and storage stability. As practical benefit the attachment to magnetic nanocarriers enabled easy enzyme recovery after repeated application runs and thus sustainable reuse. In fixed state chitinase retained a remarkable 39.7 ± 2.6 % of the starting activity after 16 reaction cycles. Furthermore, immobilized chitinase showed higher catalytic activity than free chitinase in converting shrimp shells and squid-pens chitins into di-N-acetyl chitobiose in a single-step reaction. The final yield of purified compound was 37.0 ± 1.2 % from shrimp shells and 61.1 ± 0.5 % from squid-pens chitin. In conclusion, an efficient MNP-based chitinase immobilization system with the potential for large-scale production was developed.

A new strain of Rhodococcus indonesiensis T22.7.1T and its functional potential for deacetylation of chitin and chitooligsaccharides

Introduction

Chitin, abundant in marine environments, presents significant challenges in terms of transformation and utilization. A strain, T22.7.1T, with notable chitin deacetylation capabilities, was isolated from the rhizosphere of Acanthus ebracteatus in the North Sea of China. Comparative 16S rDNA sequence analysis showed that the new isolate had the highest sequence similarity (99.79%) with Rhodococcus indonesiensis CSLK01-03T, followed by R. ruber DSM 43338T, R. electrodiphilus JC435T, and R. aetherivorans 10bc312T (98.97%, 98.81%, and 98.83%, respectively). Subsequent genome sequencing and phylogenetic analysis confirmed that strain T22.7.1T belongs to the R. indonesiensis species. However, additional taxonomic characterization identified strain T22.7.1T as a novel type strain of R. indonesiensis distinct from CSLK01-03T.

Methods

This study refines the taxonomic description of R. indonesiensis and investigates its application in converting chitin into chitosan. The chitin deacetylase (RiCDA) activity of strain T22.7.1T was optimized, and the enzyme was isolated and purified from the fermentation products.

Results

Through optimization, the RiCDA activity of strain T22.7.1T reached 287.02 U/mL, which is 34.88 times greater than the original enzyme's activity (8.0 U/mL). The natural CDA enzyme was purified with a purification factor of 31.83, and the specific activity of the enzyme solution reached 1200.33 U/mg. RiCDA exhibited good pH and temperature adaptability and stability, along with a wide range of substrate adaptabilities, effectively deacetylating chitin, chitooligosaccharides, N-acetylglucosamine, and other substrates.

Discussion

Product analysis revealed that RiCDA treatment increased the deacetylation degree (DD) of natural chitin to 83%, surpassing that of commercial chitosan. Therefore, RiCDA demonstrates significant potential as an efficient deacetylation tool for natural chitin and chitooligosaccharides, highlighting its applicability in the biorefining of natural polysaccharides.

Analysis of chitinase gene family in barley and function study of HvChi22 involved in drought tolerance

BACKGROUND

Chitinase (Chi) is a pathogenesis-related protein, also reported to play an important role in plant responses to abiotic stress. However, its role in response to abiotic stress in barley is still unclear.

RESULTS

In this study, a total of 61 Chi gene family members were identified from the whole genome of wild barley EC_S1. Phylogenetic analysis suggested that these family genes were divided into five groups. Among these genes, four pairs of collinearity genes were discovered. Besides, abundant cis-regulatory elements, including drought response element and abscisic acid response element were identified in the promoter regions of HvChi gene family members. The expression profiles revealed that most HvChi family members were significantly up-regulated under drought stress, which was also validated by RT-qPCR measurements. To further explore the role of Chi under drought stress, HvChi22 was overexpressed in Arabidopsis. Compared to wild-type plants, overexpression of HvChi22 enhanced drought tolerance by increasing the activity of oxidative protective enzymes, which caused less MDA accumulation.

CONCLUSION

Our study improved the understanding of the Chi gene family under drought stress in barley, and provided a theoretical basis for crop improvement strategies to address the challenges posed by changing environmental conditions.

The relationship between polysaccharide structure and its antioxidant activity needs to be systematically elucidated

Polysaccharides have a wide range of applications due to their excellent antioxidant activity. However, the low purity and unclear structure of polysaccharides have led some researchers to be skeptical about the antioxidant activity of polysaccharides. The current reports on the structure-activity relationship of polysaccharides are sporadic, so there is an urgent need to systematically summarize the antioxidant effects of polysaccharides with clear structures and the relationships between the structures to provide a scientific basis for the development and application of polysaccharides. This paper will systematically elucidate the structure-activity relationship of antioxidant polysaccharides, including the molecular weight, monosaccharide composition, glycosidic linkage, degree of branching, advanced conformation and chemical modification. For the first time, the antioxidant activity of polysaccharides is related to their chemical structure through histogram and radar map, and further studies using principal component analysis and cluster analysis. We critically discussed how the source, chemical structure and chemically modified groups of polysaccharides significantly contribute to their antioxidant activity and summarized the current research status and shortcomings of the structure-activity relationship of antioxidant polysaccharides. This review provides a theoretical basis and new perspective for further research on the structure-activity relationship of antioxidant polysaccharides and the development of natural antioxidants.

Eco-friendly and safe alternatives for the valorization of shrimp farming waste

The seafood industry generates waste, including shells, bones, intestines, and wastewater. The discards are nutrient-rich, containing varying concentrations of carotenoids, proteins, chitin, and other minerals. Thus, it is imperative to subject seafood waste, including shrimp waste (SW), to secondary processing and valorization for demineralization and deproteination to retrieve industrially essential compounds. Although several chemical processes are available for SW processing, most of them are inherently ecotoxic. Bioconversion of SW is cost-effective, ecofriendly, and safe. Microbial fermentation and the action of exogenous enzymes are among the significant SW bioconversion processes that transform seafood waste into valuable products. SW is a potential raw material for agrochemicals, microbial culture media, adsorbents, therapeutics, nutraceuticals, and bio-nanomaterials. This review comprehensively elucidates the valorization approaches of SW, addressing the drawbacks of chemically mediated methods for SW treatments. It is a broad overview of the applications associated with nutrient-rich SW, besides highlighting the role of major shrimp-producing countries in exploring SW to achieve safe, ecofriendly, and efficient bio-products.

Chitinases: expanding the boundaries of knowledge beyond routinized chitin degradation

Chitinases, enzymes that degrade chitin, have long been studied for their role in various biological processes. They play crucial roles in the moulting process of invertebrates, the digestion of chitinous food, and defense against chitin-bearing pathogens. Additionally, chitinases are involved in physiological functions in crustaceans, such as chitinous food digestion, moulting, and stress response. Moreover, chitinases are universally distributed in organisms from viruses to mammals and have diverse functions including tissue degradation and remodeling, nutrition uptake, pathogen invasion, and immune response regulation. The discovery of these diverse functions expands our understanding of the biological significance and potential applications of chitinases. However, recent research has shown that chitinases possess several other functions beyond just chitin degradation. Their potential as biopesticides, therapeutic agents, and tools for bioremediation underscores their significance in addressing global challenges. More importantly, we noted that they may be applied as bioweapons if ethical regulations regarding production, engineering and application are overlooked.

Insights into the molecular mechanisms, structure-activity relationships and application prospects of polysaccharides by regulating Nrf2-mediated antioxidant response

The occurrence and development of many diseases are closely related to oxidative stress. In this context, accumulating evidence suggests that Nrf2, as the master switch of cellular antioxidant signaling, plays a central role in controlling the expression of antioxidant genes. The core molecular mechanism of polysaccharides treatment of oxidative stress-induced diseases is to activate Keap1/Nrf2/ARE signaling pathway, promote nuclear translocation of Nrf2, and up-regulate the expression of antioxidant enzymes. However, recent studies have shown that other signaling pathways in which polysaccharides exert antioxidant effects, such as PI3K/Akt/GSK3β, JNK/Nrf2 and NF-κB, have complex crosstalk with Keap1/Nrf2/ARE, may have direct effects on the nuclear translocation of Nrf2. This suggests a new strategy for designing polysaccharides as modulators of Nrf2-dependent pathways to target the antioxidant response. Therefore, in this work, we investigate the crosstalk between Keap1/Nrf2/ARE and other antioxidant signaling pathways of polysaccharides by regulating Nrf2-mediated antioxidant response. For the first time, the structural-activity relationship of polysaccharides, including molecular weight, monosaccharide composition, and glycosidic linkage, is systematically elucidated using principal component analysis and cluster analysis. This review also summarizes the application of antioxidant polysaccharides in food, animal production, cosmetics and biomaterials. The paper has significant reference value for screening antioxidant polysaccharides targeting Nrf2.

Activity of a Recombinant Chitinase of the Atta sexdens Ant on Different Forms of Chitin and Its Fungicidal Effect against Lasiodiplodia theobromae

This study evaluates the activity of a recombinant chitinase from the leaf-cutting ant Atta sexdens (AsChtII-C4B1) against colloidal and solid α- and β-chitin substrates. 1H NMR analyses of the reaction media showed the formation of N-acetylglucosamine (GlcNAc) as the hydrolysis product. Viscometry analyses revealed a reduction in the viscosity of chitin solutions, indicating that the enzyme decreases their molecular masses. Both solid state 13C NMR and XRD analyses showed minor differences in chitin crystallinity pre- and post-reaction, indicative of partial hydrolysis under the studied conditions, resulting in the formation of GlcNAc and a reduction in molecular mass. However, the enzyme was unable to completely degrade the chitin samples, as they retained most of their solid-state structure. It was also observed that the enzyme acts progressively and with a greater activity on α-chitin than on β-chitin. AsChtII-C4B1 significantly changed the hyphae of the phytopathogenic fungus Lasiodiplodia theobromae, hindering its growth in both solid and liquid media and reducing its dry biomass by approximately 61%. The results demonstrate that AsChtII-C4B1 could be applied as an agent for the bioproduction of chitin derivatives and as a potential antifungal agent.

Multi-enzyme Machinery for Chitin Degradation in the Chitinolytic Bacterium Chitiniphilus shinanonensis SAY3T

The chitinolytic bacterium, Chitiniphilus shinanonensis SAY3T was examined to characterize its chitin-degrading enzymes in view of its potential to convert biomass chitin into useful saccharides. A survey of the whole-genome sequence revealed 49 putative genes encoding polypeptides that are thought to be related to chitin degradation. Based on an analysis of the relative quantity of each transcript and an assay for chitin-degrading activity of recombinant proteins, a chitin degradation system driven by 19 chitinolytic enzymes was proposed. These include sixteen endo-type chitinases, two N-acetylglucosaminidases, and one lipopolysaccharide monooxygenase that catalyzes the oxidative cleavage of glycosidic bonds. Among the 16 chitinases, ChiL was characterized by its remarkable transglycosylation activity. Of the two N-acetylglucosaminidases (ChiI and ChiT), ChiI was the major enzyme, corresponding to > 98% of the total cellular activity. Surprisingly, a chiI-disrupted mutant was still able to grow on medium with powdered chitin or GlcNAc dimer. However, its growth rate was slightly lower compared to that of the wild-type SAY3. This multi-enzyme machinery composed of various types of chitinolytic enzymes may support SAY3 to efficiently utilize native chitin as a carbon and energy source and may play a role in developing an enzymatic process to decompose and utilize abundant chitin at the industrial scale.

Properties and biotechnological applications of microbial deacetylase

Deacetylases, a class of enzymes that can catalyze the hydrolysis of acetylated substrates to remove the acetyl group, used in producing various products with high qualities, are one of the most influential industrial enzymes. These enzymes are highly specific, non-toxic, sustainable, and eco-friendly biocatalysts. Deacetylases and deacetylated compounds have been widely applicated in pharmaceuticals, medicine, food, and the environment. This review synthetically summarizes deacetylases' sources, characterizations, classifications, and applications. Moreover, the typical structural characteristics of deacetylases from different microbial sources are summarized. We also reviewed the deacetylase-catalyzed reactions for producing various deacetylated compounds, such as chitosan-oligosaccharide (COS), mycothiol, 7-aminocephalosporanic acid (7-ACA), glucosamines, amino acids, and polyamines. It is aimed to expound on the advantages and challenges of deacetylases in industrial applications. Moreover, it also serves perspectives on obtaining promising and innovative biocatalysts for enzymatic deacetylation. KEYPOINTS: • The fundamental properties of microbial deacetylases of various microorganisms are presented. • The biochemical characterizations, structures, and catalyzation mechanisms of microbial deacetylases are summarized. • The applications of microbial deacetylases in food, pharmaceutical, medicine, and the environment were discussed.

Insights into the relationships of modifying methods, structure, functional properties and applications of chitin: A review

Chitin as the second plentiful polysaccharide has arouse widely attention due to its remarkable availability and biocompatibility. While the strong inter/intra molecular hydrogen bonds and crystallinity severely restrict its applications. Recently, multiple emerging technologies are increasingly used to modify chitin structure for the sake of obtaining excellent functional properties, as well as broadening the corresponding applications. Firstly, this review systematically outlines the features of single and combined methods for chitin modification. Then, the impacts of various modifying methods on the structural characteristics of chitin, including molecular weight, degree of acetylation and functional groups, are further summarized. In addition, the effects of these structural characteristics on the functional properties as well as its potential related applications are illustrated. The conclusion of this review provides better understanding of the relationships among the modifying methods, structure, properties and applications, contributing to chitin modification for the targeted purpose in the future study.

Biochemical Properties of a Cold-Active Chitinase from Marine Trichoderma gamsii R1 and Its Application to Preparation of Chitin Oligosaccharides

The enzymatic degradation of different chitin polymers into chitin oligosaccharides (COSs) is of great significance given their better solubility and various biological applications. Chitinase plays a pivotal role in the enzymatic preparation of COSs. Herein, a cold-adapted and efficient chitinase (ChiTg) from the marine Trichoderma gamsii R1 was purified and characterized. The optimal temperature of ChiTg was 40 °C, and the relative activity at 5 °C was above 40.1%. Meanwhile, ChiTg was active and stable from pH 4.0 to 7.0. As an endo-type chitinase, ChiTg exhibited the highest activity with colloidal chitin, then with ball-milled and powdery chitin. In addition, ChiTg showed high efficiency when hydrolyzing colloidal chitin at different temperatures, and the end products were mainly composed of COSs with one to three degrees of polymerization. Furthermore, the results of bioinformatics analysis revealed that ChiTg belongs to the GH18 family, and its acidic surface and the flexible structure of its catalytic site may contribute to its high activity in cold conditions. The results of this study provide a cold-active and efficient chitinase and ideas for its application regarding the preparation of COSs from colloidal chitin.

Novel Chitin Deacetylase from Thalassiosira weissflogii Highlights the Potential for Chitin Derivative Production

β-Chitin is an important carbon fixation product of diatoms, and is the most abundant nitrogen-containing polysaccharide in the ocean. It has potential for widespread application, but the characterization of chitin-related enzymes from β-chitin producers has rarely been reported. In this study, a chitin deacetylase (TwCDA) was retrieved from the Marine Microbial Eukaryote Transcriptome Sequencing Project (MMETSP) database and was heterologously expressed in vitro for functional analysis. The results showed that both the full-length sequence (TwCDA) and the N-terminal truncated sequence (TwCDA-S) had chitin deacetylase and chitinolytic activities after expression in Escherichia coli. High-performance liquid chromatography (HPLC) and gas chromatography–mass spectrometry (GC-MS) indicated that TwCDA and TwCDA-S could catalyze the deacetylation of oligosaccharide (GlcNAc)5. TwCDA had higher deacetylase activity, and also catalyzed the deacetylation of the β-chitin polymer. A dinitrosalicylic acid (DNS) assay showed that TwCDA-S had high chitinolytic activity for (GlcNAc)5, and the optimal reaction temperature was 35 °C. Liquid chromatography combined with time-of-flight mass spectrometry (LC-coTOF-MS) detected the formation of a N-acetylglucosamine monomer (C8H15NO6) in the reaction mixture. Altogether, we isolated a chitin deacetylase from a marine diatom, which can catalyze the deacetylation and degradation of chitin and chitin oligosaccharides. The relevant results lay a foundation for the internal regulation mechanism of chitin metabolism in diatoms and provide a candidate enzyme for the green industrial preparation of chitosan and chitin oligosaccharides.

Recent trends in nanocomposite packaging films utilising waste generated biopolymers: Industrial symbiosis and its implication in sustainability

Uncontrolled waste generation and management difficulties are causing chaos in the ecosystem. Although it is vital to ease environmental pressures, right now there is no such practical strategy available for the treatment or utilisation of waste material. Because the Earth's resources are limited, a long-term, sustainable, and sensible solution is necessary. Currently waste material has drawn a lot of attention as a renewable resource. Utilisation of residual biomass leftovers appears as a green and sustainable approach to lessen the waste burden on Earth while meeting the demand for bio-based goods. Several biopolymers are available from renewable waste sources that have the potential to be used in a variety of industries for a wide range of applications. Natural and synthetic biopolymers have significant advantages over petroleum-based polymers in terms of cost-effectiveness, environmental friendliness, and user-friendliness. Using waste as a raw material through industrial symbiosis should be taken into account as one of the strategies to achieve more economic and environmental value through inter-firm collaboration on the path to a near-zero waste society. This review extensively explores the different biopolymers which can be extracted from several waste material sources and that further have potential applications in food packaging industries to enhance the shelf life of perishables. This review-based study also provides key insights into the different strategies and techniques that have been developed recently to extract biopolymers from different waste byproducts and their feasibility in practical applications for the food packaging business.

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.

Chitosan: An Autocidal Molecule of Plant Pathogenic Fungus

The rise in the world's food demand with the increasing population threatens the existence of civilization with two equally valuable concerns: increase in global food production and sustainability in the ecosystem. Furthermore, biotic and abiotic stresses are adversely affecting agricultural production. Among them, losses caused by insect pests and pathogens have been shown to be more destructive to agricultural production. However, for winning the battle against the abundance of insect pests and pathogens and their nature of resistance development, the team of researchers is searching for an alternative way to minimize losses caused by them. Chitosan, a natural biopolymer, coupled with a proper application method and effective dose could be an integral part of sustainable alternatives in the safer agricultural sector. In this review, we have integrated the insight knowledge of chitin-chitosan interaction, successful and efficient use of chitosan, recommended and practical methods of use with well-defined doses, and last but not least the dual but contrast mode of action of the chitosan in hosts and as well as in pathogens.

A Novel Potent Crystalline Chitin Decomposer: Chitin Deacetylase from Acinetobacter schindleri MCDA01

Chitosan is a functional ingredient that is widely used in food chemistry as an emulsifier, flocculant, antioxidant, or preservative. Chitin deacetylases (CDAs) can catalyze the hydrolysis of acetyl groups, making them useful in the clean production of chitosan. However, the high inactivity of crystalline chitin catalyzed by CDAs has been regarded as the technical bottleneck of crystalline chitin deacetylation. Here, we mined the AsCDA gene from the genome of Acinetobacter schindleri MCDA01 and identified a member of the uraD_N-term-dom superfamily, which was a novel chitin deacetylase with the highest deacetylation activity. The AsCDA gene was expressed in Escherichia coli BL21 by IPTG induction, whose activity to colloidal chitin, α-chitin, and β-chitin reached 478.96 U/mg, 397.07 U/mg, and 133.27 U/mg, respectively. In 12 h, the enzymatic hydrolysis of AsCDA removed 63.05% of the acetyl groups from α-chitin to prepare industrial chitosan with a degree of deacetylation higher than 85%. AsCDA, as a potent chitin decomposer in the production of chitosan, plays a positive role in the upgrading of the chitosan industry and the value-added utilization of chitin biological resources.

Enzymatic modification of native chitin and chitin oligosaccharides by an alkaline chitin deacetylase from Microbacterium esteraromaticum MCDA02

In this study, chitin deacetylase from Microbacterium esteraromaticum MCDA02 (MeCDA) was purified by ammonium sulfate precipitation, anion exchange chromatography, and superdex column chromatography. The molecular weight of purified MeCDA was approximately 26 kDa. The optimum pH and temperature of purified MeCDA were 8.0 and 30 °C, respectively. The enzyme activity is enhanced by metal ions K⁺ and Sr⁺ and inhibited by Co²⁺, Cd²⁺, and EDTA. The degree of deacetylation through enzymatic modification of MeCDA was removed an average of 32.75% of the acetyl groups for ɑ-chitin by acid-base titration. Meanwhile, MeCDA can catalyze the hydrolytic cleavage of the acetamido bond in GlcNAc units within chitin oligomers and polymers. Hence, the MeCDA is a potent chitin decomposer to catalyze chitin and chitin oligosaccharides deacetylation to prepare chitosan and chitosan oligosaccharide. This is a value-added utilization of chitin based biological resources.

Microbial decomposition of crustacean shell for production of bioactive metabolites and study of its fertilizing potential

Crustacean shell waste disposal is considered as biggest problem in seafood processing centers. Incineration and landfilling are the commonest ways of disposal of the waste which causes environmental pollution. Microbial bio-conversion is one of the promising approaches to minimize the wastes by utilizing the same for deriving different value added metabolites. In this perspective, chitinase- and protease-producing bacterial strains were isolated from shrimp culture pond, and the potent isolate was subsequently identified as Alcaligenes faecalis SK10. Fermentative optimization of the production of chitinase (85.42 U/ml), protease (58.57 U/ml), and their catalytic products, viz., N-acetylamino sugar (84 μg/ml) and free amino acids (112 μg/ml), were carried out by utilizing shrimp and crab shell powder as principal substrate. The fermented hydrolysate (FH) was subsequently applied to evaluate its potential to be a candidate fertilizer for the growth of leguminous plant Pisum sativum and Cicer arietinum, and the results were compared with chitin, chitosan, and commercial biofertilizer amended group. The results revealed that FH have paramount potential to improve plants morpho-physiological parameters like stem and root length, chlorophyll, cellular RNA, protein content, and soil physico-chemical parameters like total nitrogen, magnesium, calcium, phosphorus, and potassium significantly (p < 0.05). Moreover, the application of FH also selectively encouraged the growth of free-living nitrogen-fixing bacteria, Rhizobium, phosphate-solubilizing bacteria in the soil by 4.82- and 5.27-, 5.57- and 4.71, and 7.64- and 6.92-fold, respectively, in the rhizosphere of P. sativum and C. arietinum, which collectively is a good sign for an ideal biofertilizer. Co-supplementation of FH with commercial PGPR-biofertilizer significantly influenced the morpho-physiological attributes of plant and physico-chemical and microbial attributes of soil. The study validated proficient and sustainable utilization of fermented hydrolysate of waste crustacean shell as biofertilizer.

Enzymatic approaches in the bioprocessing of shellfish wastes

Several tonnes of shellfish wastes are generated globally due to the mass consumption of shellfish meat from crustaceans like prawn, shrimp, lobster, crab, Antarctic krill, etc. These shellfish wastes are a reservoir of valuable by-products like chitin, protein, calcium carbonate, and pigments. In the present scenario, these wastes are treated chemically to recover chitin by the chitin and chitosan industries, using hazardous chemicals like HCl and NaOH. Although this process is efficient in removing proteins and minerals, the unscientific dumping of harmful effluents is hazardous to the ecosystem. Stringent environmental laws and regulations on waste disposal have encouraged researchers to look for alternate strategies to produce near-zero wastes on shellfish degradation. The role of enzymes in degrading shellfish wastes is advantageous yet has not been explored much, although it produces bioactive rich protein hydrolysates with good quality chitin. The main objective of the review is to discuss the potential of various enzymes involved in shellfish degradation and their opportunities and challenges over chemical processes in chitin recovery.

Enzymatic Synthesis and Characterization of Different Families of Chitooligosaccharides and Their Bioactive Properties

Chitooligosaccharides (COS) are homo- or hetero-oligomers of D-glucosamine (GlcN) and N-acetyl-D-glucosamine (GlcNAc) that can be obtained by chitosan or chitin hydrolysis. Their enzymatic production is preferred over other methodologies (physical, chemical, etc.) due to the mild conditions required, the fewer amounts of waste and its efficiency to control product composition. By properly selecting the enzyme (chitinase, chitosanase or nonspecific enzymes) and the substrate properties (degree of deacetylation, molecular weight, etc.), it is possible to direct the synthesis towards any of the three COS types: fully acetylated (faCOS), partially acetylated (paCOS) and fully deacetylated (fdCOS). In this article, we review the main strategies to steer the COS production towards a specific group. The chemical characterization of COS by advanced techniques, e.g., high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) and MALDI-TOF mass spectrometry, is critical for structure–function studies. The scaling of processes to synthesize specific COS mixtures is difficult due to the low solubility of chitin/chitosan, the heterogeneity of the reaction mixtures, and high amounts of salts. Enzyme immobilization can help to minimize such hurdles. The main bioactive properties of COS are herein reviewed. Finally, the anti-inflammatory activity of three COS mixtures was assayed in murine macrophages after stimulation with lipopolysaccharides.

In Silico Studies of Lamiaceae Diterpenes with Bioinsecticide Potential against Aphis gossypii and Drosophila melanogaster

Background: The growing demand for agricultural products has led to the misuse/overuse of insecticides; resulting in the use of higher concentrations and the need for ever more toxic products. Ecologically, bioinsecticides are considered better and safer than synthetic insecticides; they must be toxic to the target organism, yet with low or no toxicity to non-target organisms. Many plant extracts have seen their high insecticide potential confirmed under laboratory conditions, and in the search for plant compounds with bioinsecticidal activity, the Lamiaceae family has yielded satisfactory results. Objective: The aim of our study was to develop computer-assisted predictions for compounds with known insecticidal activity against Aphis gossypii and Drosophila melanogaster. Results and conclusion: Structure analysis revealed ent-kaurane, kaurene, and clerodane diterpenes as the most active, showing excellent results. We also found that the interactions formed by these compounds were more stable, or presented similar stability to the commercialized insecticides tested. Overall, we concluded that the compounds bistenuifolin L (1836) and bistenuifolin K (1931), were potentially active against A. gossypii enzymes; and salvisplendin C (1086) and salvixalapadiene (1195), are potentially active against D. melanogaster. We observed and highlight that the diterpenes bistenuifolin L (1836), bistenuifolin K (1931), salvisplendin C (1086), and salvixalapadiene (1195), present a high probability of activity and low toxicity against the species studied.

A bottom-up approach towards a bacterial consortium for the biotechnological conversion of chitin to L-lysine

Chitin is an abundant waste product from shrimp and mushroom industries and as such, an appropriate secondary feedstock for biotechnological processes. However, chitin is a crystalline substrate embedded in complex biological matrices, and, therefore, difficult to utilize, requiring an equally complex chitinolytic machinery. Following a bottom-up approach, we here describe the step-wise development of a mutualistic, non-competitive consortium in which a lysine-auxotrophic Escherichia coli substrate converter cleaves the chitin monomer N-acetylglucosamine (GlcNAc) into glucosamine (GlcN) and acetate, but uses only acetate while leaving GlcN for growth of the lysine-secreting Corynebacterium glutamicum producer strain. We first engineered the substrate converter strain for growth on acetate but not GlcN, and the producer strain for growth on GlcN but not acetate. Growth of the two strains in co-culture in the presence of a mixture of GlcN and acetate was stabilized through lysine cross-feeding. Addition of recombinant chitinase to cleave chitin into GlcNAc₂, chitin deacetylase to convert GlcNAc₂ into GlcN₂ and acetate, and glucosaminidase to cleave GlcN₂ into GlcN supported growth of the two strains in co-culture in the presence of colloidal chitin as sole carbon source. Substrate converter strains secreting a chitinase or a β-1,4-glucosaminidase degraded chitin to GlcNAc₂ or GlcN₂ to GlcN, respectively, but required glucose for growth. In contrast, by cleaving GlcNAc into GlcN and acetate, a chitin deacetylase-expressing substrate converter enabled growth of the producer strain in co-culture with GlcNAc as sole carbon source, providing proof-of-principle for a fully integrated co-culture for the biotechnological utilization of chitin.

Structure-function analysis of Gynuella sunshinyii chitosanase uncovers the mechanism of substrate binding in GH family 46 members

Chitooligosaccharides (COS) is a kind of functional carbohydrates with great application potential as its various biological functions in food, cosmetics, and pharmaceutical fields. Exploring the relationship between structure and function of chitosanase is essential for the controllable preparation of chitooligosaccharides with the specific degree of polymerization (DP). GsCsn46A is a cold-adapted glycosyl hydrolase (GH) family 46 chitosanase with application potential for the controllable preparation of chitooligosaccharides. Here, we present two complex structures with substrate chitopentaose and chitotetraose of GsCsn46A, respectively. The overall structure of GsCsn46A contains nine α-helices and two β-strands that folds into two globular domains with the substrate between them. The unique binding positions of both chitopentaose and chitotetraose revealed two novel sugar residues in the negatively-numbered subsites of GH family 46 chitosanases. The structure-function analysis of GsCsn46A uncovers the substrate binding and catalysis mechanism of GH family 46 chitosanases. Structural basis mutagenesis in GsCsn46A indicated that altering interactions near +3 subsite would help produce hydrolysis products with higher DP. Specifically, the mutant N21W of GsCsn46A nearly eliminated the ability of hydrolyzing chitotetraose after long-time degradation.

Preparation of Defined Chitosan Oligosaccharides Using Chitin Deacetylases

During the past decade, detailed studies using well-defined 'second generation' chitosans have amply proved that both their material properties and their biological activities are dependent on their molecular structure, in particular on their degree of polymerisation (DP) and their fraction of acetylation (F_A). Recent evidence suggests that the pattern of acetylation (PA), i.e., the sequence of acetylated and non-acetylated residues along the linear polymer, is equally important, but chitosan polymers with defined, non-random PA are not yet available. One way in which the PA will influence the bioactivities of chitosan polymers is their enzymatic degradation by sequence-dependent chitosan hydrolases present in the target tissues. The PA of the polymer substrates in conjunction with the subsite preferences of the hydrolases determine the type of oligomeric products and the kinetics of their production and further degradation. Thus, the bioactivities of chitosan polymers will at least in part be carried by the chitosan oligomers produced from them, possibly through their interaction with pattern recognition receptors in target cells. In contrast to polymers, partially acetylated chitosan oligosaccharides (paCOS) can be fully characterised concerning their DP, F_A, and PA, and chitin deacetylases (CDAs) with different and known regio-selectivities are currently emerging as efficient tools to produce fully defined paCOS in quantities sufficient to probe their bioactivities. In this review, we describe the current state of the art on how CDAs can be used in forward and reverse mode to produce all of the possible paCOS dimers, trimers, and tetramers, most of the pentamers and many of the hexamers. In addition, we describe the biotechnological production of the required fully acetylated and fully deacetylated oligomer substrates, as well as the purification and characterisation of the paCOS products.

Vibrio campbellii chitoporin: Thermostability study and implications for the development of therapeutic agents against Vibrio infections

Vibrio campbellii (formerly Vibrio harveyi) is a bacterial pathogen that causes vibriosis, which devastates fisheries and aquaculture worldwide. V. campbellii expresses chitinolytic enzymes and chitin binding/transport proteins, which serve as excellent targets for antimicrobial agent development. We previously characterized VhChiP, a chitooligosaccharide-specific porin from the outer membrane of V. campbellii BAA-1116. This study employed far-UV circular dichroism and tryptophan fluorescence spectroscopy, together with single channel electrophysiology to demonstrate that the strong binding of chitoligosaccharides enhanced thermal stability of VhChiP. The alanine substitution of Trp¹³⁶ at the center of the affinity sites caused a marked decrease in the binding affinity and decreased the thermal stability of VhChiP. Tryptophan fluorescence titrations over a range of temperatures showed greater free-energy changes on ligand binding (ΔG°_binding) with increasing chain length of the chitooligosaccharides. Our findings suggest the possibility of designing stable channel-blockers, using sugar-based analogs that serve as antimicrobial agents, active against Vibrio infection.

Endo-chitinase Chit33 specificity on different chitinolytic materials allows the production of unexplored chitooligosaccharides with antioxidant activity

The biological activity of chitooligosaccharides (COS) has made them targets for industrial and medical sectors. In this work, endo-chitinase Chit33 from Trichoderma harzianum CECT 2413 was expressed in Pichia pastoris GS115 to levels never achieved before (630 mg/L; 3.3 U/mL), without its biochemical characteristics being substantially affected. Chit33 produced a mixture of fully and partially acetylated COS from different chitin derivatives. HPAEC-PAD Chromatography and mass spectrometry analyses showed that (GlcNAc)₄ and GlcN-(GlcNAc)₂ were mainly produced from colloidal chitin and chitosan, respectively. COS in reaction mixtures were fragmented according to their size and their antioxidant activity analyzed by reducing power and free radical scavenging activity essays. The highest antioxidant activity was achieved with COS in the range of 0.5-2 and 2-10 kDa produced from colloidal chitin and chitosan, respectively, which gives biotechnological potential to both the chitin derivatives of 0.5-10 kDa and the biocatalyst producing them.