Biodegradation of shrimp processing bio-waste and concomitant production of chitinase enzyme and N-acetyl-D-glucosamine by marine bacteria: production and process optimization

Establishment of the colloidal chitin enzymatic hydrolysis conditions to obtain N-acetyl glucosamine

The wastes generated by the shrimp industry are approximately between 50 and 60% of the catch volume. These residues such as head, viscera, and shell are potential pollutants if they are not treated for proper disposal. One way to solve this problem is to use the residues as functional food ingredients. In this regard, shrimp residues are rich in chitin, the second most abundant biopolymer on the planet after cellulose. Chitin is composed of N-acetyl glucosamine, a molecule used as a sweetener in the food industry and as an aid in the treatment of coronary diseases and gonarthrosis. N-acetyl glucosamine can be obtained by the hydrolysis of colloidal chitin using chemical or enzymatic methods; however, chemical methods are associated with pollution. In this study, we determined the hydrolysis conditions of shrimp colloidal chitin for obtaining N-acetyl glucosamine, using the extracellular enzymes produced by a marine bacterium isolated in the coastal zone of Progreso, Yucatan, Mexico. The best N-acetyl glucosamine yield obtained was 2.65%, using 10 mg/mL colloidal chitin, at 60°C, and pH 8.9 with 3.5% NaCl.

A novel sucrose-inducible expression system and its application for production of biomass-degrading enzymes in Aspergillus niger

BACKGROUND

Filamentous fungi are extensively exploited as important enzyme producers due to the superior secretory capability. However, the complexity of their secretomes greatly impairs the titer and purity of heterologous enzymes. Meanwhile, high-efficient evaluation and production of bulk enzymes, such as biomass-degrading enzymes, necessitate constructing powerful expression systems for bio-refinery applications.

RESULTS

A novel sucrose-inducible expression system based on the host strain Aspergillus niger ATCC 20611 and the β-fructofuranosidase promoter (PfopA) was constructed. A. niger ATCC 20611 preferentially utilized sucrose for rapid growth and β-fructofuranosidase production. Its secretory background was relatively clean because β-fructofuranosidase, the key enzyme responsible for sucrose utilization, was essentially not secreted into the medium and the extracellular protease activity was low. Furthermore, the PfopA promoter showed a sucrose concentration-dependent induction pattern and was not subject to glucose repression. Moreover, the strength of PfopA was 7.68-fold higher than that of the commonly used glyceraldehyde-3-phosphate dehydrogenase promoter (PgpdA) with enhanced green fluorescence protein (EGFP) as a reporter. Thus, A. niger ATCC 20611 coupled with the PfopA promoter was used as an expression system to express a β-glucosidase gene (bgla) from A. niger C112, allowing the production of β-glucosidase at a titer of 17.84 U/mL. The crude β-glucosidase preparation could remarkably improve glucose yield in the saccharification of pretreated corncob residues when added to the cellulase mixture of Trichoderma reesei QM9414. The efficacy of this expression system was further demonstrated by co-expressing the T. reesei-derived chitinase Chi46 and β-N-acetylglucosaminidase Nag1 to obtain an efficient chitin-degrading enzyme cocktail, which could achieve the production of N-acetyl-D-glucosamine from colloidal chitin with a conversion ratio of 91.83%. Besides, the purity of the above-secreted biomass-degrading enzymes in the crude culture supernatant was over 86%.

CONCLUSIONS

This PfopA-driven expression system expands the genetic toolbox of A. niger and broadens the application field of the traditional fructo-oligosaccharides-producing strain A. niger ATCC 20611, advancing it to become a high-performing enzyme-producing cell factory. In particular, the sucrose-inducible expression system possessed the capacity to produce biomass-degrading enzymes at a high level and evade endogenous protein interference, providing a potential purification-free enzyme production platform for bio-refinery applications.

Antifungal Agent Chitooligosaccharides Derived from Solid-State Fermentation of Shrimp Shell Waste by Pseudonocardia antitumoralis 18D36-A1

Shrimp shell waste is a potential source of the biopolymer chitin. Through fermentation, chitin can be converted into its derivative products. This study aimed to isolate and characterize the products of the biodegradation of chitin from shrimp shell waste through a solid-state fermentation process using actinomycetes. Actinomycete isolates were obtained from tunicate marine biota collected from the waters of Buleleng, Bali, using a dilution technique on 1% chitin colloid agar medium. The isolated actinomycetes were cultivated on a shrimp shell waste medium for 7 days, and then the products of the biodegradation of the oligomers were extracted using water. The extracts of the biodegradation products of the shrimp shells were isolated through several chromatographic steps and analyzed using LC–MS–MS, and the bioactivity of the biodegradation products against fungi was tested. The morphological observations and phylogenetic analysis showed that the isolate 18D36-A1 was a rare actinomycete with the proposed name Pseudonocardia antitumoralis 18D36-A1. The results of the analysis using TLC showed that the solid-state fermented water isolate 18D36-A1 produced several oligomeric components. These results indicate that the isolate 18D36-A1 was able to convert chitin into chitooligosaccharides. Further isolation of the extract produced the active fraction D36A1C38, which can inhibit the growth of fungi by 74% at a concentration of 1 mg/mL. This initial information is very important for further studies related to the development of a solid-state fermentation process for obtaining bioactive compounds from shrimp shell waste.

Increased production of chitinase by a Paenibacillus illinoisensis isolated from Brazilian coastal soil when immobilized in alginate beads

The accumulation of chitin waste from the seafood industry is a serious environmental problem. However, this residue can be degraded by chitinases and its subproducts, such as chitosan, economically exploited. In this study, a chitinase producer bacteria, identified as Paenibacillus illinoisensis, was isolated from the Brazilian coastal city of Terra de Areia - Rio Grande Do Sul (RS) and was immobilized within alginate beads to evaluate its chitinase production. The alginate beads containing cells presented an average size of 4 mm, 99% of immobilization efficiency and increased the enzymatic activity in 40.71% compared to the free cells. The biomass during enzymatic production increased 62.01% and the total cells leaked from the alginate beads corresponded to 6.46% after 96 h. Immobilized cells were reused in a sequential batch system and remained stable for production for up to four 96-h cycles, decreasing only 21.04% of the initial activity at the end of the fourth cycle. Therefore, the methodology used for cell immobilization resulted in adequate beads to maintain cell viability during the enzymatic production, increasing enzymatic activity, showing low cell leakage from the support and appropriate recyclable capacity.

Multiple Metabolic Phenotypes as Screening Criteria Are Correlated With the Plant Growth-Promoting Ability of Rhizobacterial Isolates

Efficient screening method is the prerequisite for getting plant growth-promoting (PGP) rhizobacteria (PGPR) which may play an important role in sustainable agriculture from the natural environment. Many current traditional preliminary screening criteria based on knowledge of PGP mechanisms do not always work well due to complex plant-microbe interactions and may lead to the low screening efficiency. More new screening criteria should be evaluated to establish a more effective screening system. However, the studies focused on this issue were not enough, and few new screening criteria had been proposed. The aim of this study was to analyze the correlation between the metabolic phenotypes of rhizobacterial isolates and their PGP ability. The feasibility of using these phenotypes as preliminary screening criteria for PGPR was also evaluated. Twenty-one rhizobacterial isolates were screened for their PGP ability, traditional PGP traits, and multiple metabolic phenotypes that are not directly related to PGP mechanisms, but are possibly related to rhizosphere colonization. Correlations between the PGP traits or metabolic phenotypes and increases in plant agronomic parameters were analyzed to find the indicators that are most closely related to PGP ability. The utilization of 11 nutrient substrates commonly found in root exudates, such as D-salicin, β-methyl-D-glucoside, and D-cellobiose, was significantly positively correlated with the PGP ability of the rhizobacterial isolates. The utilization of one amino acid and two organic acids, namely L-aspartic acid, α-keto-glutaric acid, and formic acid, was negatively correlated with PGP ability. There were no significant correlations between four PGP traits tested in this study and the PGP ability. The ability of rhizobacterial isolates to metabolize nutrient substrates that are identical or similar to root exudate components may act as better criteria than PGP traits for the primary screening of PGPR, because rhizosphere colonization is a prerequisite for PGPR to affect plants.

Valorization of Seafood Processing Discards: Bioconversion and Bio-Refinery Approaches

The seafood industry generates large volumes of waste. These include processing discards consisting of shell, head, bones intestine, fin, skin, voluminous amounts of wastewater discharged as effluents, and low-value under-utilized fish, which are caught as by-catch of commercial fishing operations. The discards, effluents, and by-catch are rich in nutrients including proteins, amino acids, lipids containing good proportions of polyunsaturated fatty acids (PUFA), carotenoids, and minerals. The seafood waste is, therefore, responsible for loss of nutrients and serious environmental hazards. It is important that the waste is subjected to secondary processing and valorization to address the problems. Although chemical processes are available for waste treatment, most of these processes have inherent weaknesses. Biological treatments, however, are environmentally friendly, safe, and cost-effective. Biological treatments are based on bioconversion processes, which help with the recovery of valuable ingredients from by-catch, processing discards, and effluents, without losing their inherent bioactivities. Major bioconversion processes make use of microbial fermentations or actions of exogenously added enzymes on the waste components. Recent developments in algal biotechnology offer novel processes for biotransformation of nutrients as single cell proteins, which can be used as feedstock for the recovery of valuable ingredients and also biofuel. Bioconversion options in conjunction with a bio-refinery approach have potential for eco-friendly and economical management of seafood waste that can support sustainable seafood production.

Sustainable and eco-friendly strategies for shrimp shell valorization

Among the seafood used globally, shellfish consumption is in great demand. The utilization of these shellfish such as prawn/shrimp has opened a new market for the utilization of the shellfish wastes. Considering the trends on the production of wealth from wastes, shrimp shell wastes seem an important resource for the generation of high value products when processed on the principles of a biorefinery. In recent years, various chemical strategies have been tried to valorize the shrimp shell wastes, which required harsh chemicals such as HCl and NaOH for demineralization (DM) and deproteination (DP) of the shrimp wastes. Disposal of chemicals by the chitin and chitosan industries into the aquatic bodies pose harm to the aquatic flora and fauna. Thus, there has been intensive efforts to develop safe and sustainable technologies for the management of shrimp shell wastes. This review provides an insight about environmentally-friendly methods along with biological methods to valorize the shrimp waste compared to the strategies employing concentrated chemicals. The main objective of this review article is to explain the utilization shrimp shell wastes in a productive manner such that it would be offer environment and economic sustainability. The application of valorized by-products developed from the shrimp shell wastes and physical methods to improve the pretreatment process of shellfish wastes for valorization are also highlighted in this paper.

Chitinolytic proteins secreted by Cellulosimicrobium sp. NTK2

Cellulosimicrobium sp. NTK2 (NTK2 strain) was isolated as a chitinolytic bacterium from mature compost derived from chitinous waste. The growth of the NTK2 strain was enhanced by supplementation of the culture medium with 2% crystalline chitin. Approximately 70% of the supplemented crystalline chitin was degraded during cultivation. Whole genome analysis of the NTK2 strain identified eight chitinases and two chitin-binding proteins. The NTK2 strain secreted two bacterial extracellular solute-binding proteins, three family 18 glycosyl hydrolases and one lytic polysaccharide monooxygenase specifically in the presence of crystalline chitin. A chitinolytic enzyme with a molecular mass of 29 kDa on SDS-PAGE under native conditions was also secreted. This chitinolytic enzyme exhibited the largest band upon zymography but could not be identified. In an attempt to identify all the chitinases secreted by the NTK2 strain, we expressed recombinant versions of the proteins exhibiting chitinolytic activity in Escherichia coli. Our results suggest that the 29 kDa protein belonging to family 19 glycosyl hydrolase was expressed specifically in the presence of 2% crystalline chitin.

Optimization of media components for the production of N-acetylchitooligosaccharide from chitin by Streptomyces chilikensis through Taguchi experimental design

Optimization of media composition for microbial growth is crucial particularly in industrial processes to obtain the desired end product. The waste from sea food industries includes the non-edible parts of shrimp, crabs and prawns which are rich in chitin as the major cause of pollution in coastal areas. Chitin degradation is carried out chemically. It can be degraded biologically also, particularly using microorganisms resulting in chitooligosaccahrides and the monomer N-acetylglucosamine. N-acetyl glucosamine and related chitooligosaccahrides have various applications such as treatment of cancer and metastasis, treatment of autoimmune reactions, as food supplements and increased plant stress tolerance against salinity and heavy metals. Thus, chitin waste can be efficiently degraded biologically using microorganisms to produce such useful products. Conventional methods such as One factor at a time (OFAT) are more time consuming and costly to address the problem. The current work focuses on the development of an experimental design to ascertain parameters optimized for chitin degradation by a Streptomyces chilikensis to produce various chitooligosaccharides. More than one factor was taken at a time to carry out the experiments and the data were fit into Taguchi Design to determine the contribution of the most important factors responsible for the production of the desired end product that is NAG and other chitooligosaccaharides. Highest NAG production (3741 μM/reaction) was observed in a media that contains 0.5% Raffinose (w/v), 0.5% peptone (w/v), 2.5% NaCl at pH 11.

Isolation and identification of marine strains of Stenotrophomona maltophilia with high chitinolytic activity

Chitin is the second most abundant organic compound in nature and represents a rich carbon and nitrogen source that is primarily transformed by bacterial communities. Bacteria capable of gradually hydrolyzing chitin into N-acetylglucosamine monomers can have applications in the transformation of residues from shrimp and other crustaceans. The objective of the present study was to isolate, characterize and identify microorganisms with high chitinolytic activity. These microorganisms were isolated and characterized based on macro- and microscopic morphological traits. Strains were selected on colloidal chitin agar medium primarily based on a hydrolysis halo larger than 2 mm and a growing phase no longer than 6 days. Secondary selection consisted of semi-quantitative evaluation of chitinolytic activity with a drop dilution assay. From the above, ten strains were selected. Then, strain-specific activity was evaluated. The B4 strain showed the highest specific activity, which was 6,677.07 U/mg protein. Molecular identification indicated that the isolated strains belong to the species Stenotrophomonas maltophilia.

Production of chitinase from thermophilic Humicola grisea and its application in production of bioactive chitooligosaccharides

A novel thermophilic chitinase producing strain Humicola grisea ITCC 10,360.16 was isolated from soil of semi-arid desert region of Rajasthan. Maximum enzyme production (116±3.45Ul^-1) was achieved in submerged fermentation. Nutritional requirement for maximum production of chitinase under submerged condition was optimized using response surface methodology. Among the eight nutritional elements studied, chitin, colloidal chitin, KCl and yeast-extract were identified as the most critical variables for chitinase production by Plackett-Burman design first. Further optimization of these variables was done by four-factor central composite design. The model came out to be significant and statistical analysis of results showed that an appropriate ratio of chitin and colloidal chitin had resulted into enhancement in enzyme production levels. Optimum concentration of the variables for enhanced chitinase production were 7.49, 4.91, 0.19 and 5.50 (gl^-1) for chitin, colloidal chitin, KCl and yeast extract, respectively. 1.43 fold enhancement in chitinase titres was attained in shake flasks, when the variables were used at their optimum levels. Thin layer chromatography revealed that enzyme can effectively hydrolyze colloidal chitin to produce chitooligosaccharides. Chitinase production from H. grisea and optimization of economic production medium heighten the employment of enzyme for large scale production of bioactive chitooligosaccharides.

Short-Chain Chitin Oligomers: Promoters of Plant Growth

Chitin is the second most abundant biopolymer in nature after cellulose, and it forms an integral part of insect exoskeletons, crustacean shells, krill and the cell walls of fungal spores, where it is present as a high-molecular-weight molecule. In this study, we showed that a chitin oligosaccharide of lower molecular weight (tetramer) induced genes in Arabidopsis that are principally related to vegetative growth, development and carbon and nitrogen metabolism. Based on plant responses to this chitin tetramer, a low-molecular-weight chitin mix (CHL) enriched to 92% with dimers (2mer), trimers (3mer) and tetramers (4mer) was produced for potential use in biotechnological processes. Compared with untreated plants, CHL-treated plants had increased in vitro fresh weight (10%), radicle length (25%) and total carbon and nitrogen content (6% and 8%, respectively). Our data show that low-molecular-weight forms of chitin might play a role in nature as bio-stimulators of plant growth, and they are also a known direct source of carbon and nitrogen for soil biomass. The biochemical properties of the CHL mix might make it useful as a non-contaminating bio-stimulant of plant growth and a soil restorer for greenhouses and fields.

Chitin degradation and electricity generation by Aeromonas hydrophila in microbial fuel cells

Chitin is one of the most abundant biopolymers in nature and the main composition of shrimp and crab shells (usually as food wastes). Thus it is essential to investigate the potential of degrading chitin for energy recovery. This study investigated the anaerobic degradation of chitin by Aeromonas hydrophila, a chitinolytic and popular electroactive bacterium, in both fermentation and microbial fuel cell (MFC) systems. The primary chitin metabolites produced in MFC were succinate, lactate, acetate, formate, and ethanol. The total metabolite concentration from chitin degradation increased seven-fold in MFC compared to the fermentation system, as well as additional electricity generation. Moreover, A. hydrophila degraded GlcNAc (the intermediate of chitin hydrolysis) significantly faster (0.97 and 0.94 mM C/d/mM-GlcNAc) than chitin (0.13 and 0.03 mM C/d/mM-GlcNAc) in MFC and fermentation systems, indicating that extracellular hydrolysis of chitin was the rate-limiting step and this step could be accelerated in MFC. Furthermore, more chemicals produced by the addition of exogenous mediators in MFC. This study proves that the chitin could be degraded effectively by an electroactive bacterium in MFC, and our results suggest that this bioelectrochemical system might be useful for the degradation of recalcitrant biomass to recover energy.

Microbial collagenases: challenges and prospects in production and potential applications in food and nutrition

Microbial collagenases are promising enzymes in view of their extensive industrial and biological applications.

High antioxidant and DNA protection activities of N-acetylglucosamine (GlcNAc) and chitobiose produced by exolytic chitinase from Bacillus cereus EW5

Chitin-degrading bacterial strains were screened and tested for their ability to degrade shrimp-shell waste (SSW). Among the potential strains, B. cereus EW5 exhibited the highest chitin-degrading ability compared with other strains and produced 24 mg of reducing sugar per gram of dry SSW after 4 days of incubation. A TLC analysis of SSW biodegradation revealed that the chitosaccharides produced in the culture supernatant were mainly N-acetylglucosamine (GlcNAc) and chitobiose due to the isolate’s exolytic chitinase activity. The culture supernatant exhibited a high degree of antioxidant activity, as indicated by 83% DPPH, 99.6% ABTS, 51% hydroxyl radical scavenging activity and 0.34 reducing power. The formation of GlcNAc and chitobiose during biodegradation of SSW is considered to be the major contributor to the antioxidant activity. The EW5 culture supernatant also displayed inhibition of DNA damage, enhancing the reutilization value of SSW. This report presents the first description of fermented production of GlcNAc and DNA protective activity of culture supernatant from SSW by B. cereus.

Optimization of conditions for isolation of high quality chitin from shrimp processing raw byproducts using response surface methodology and its characterization

Chitin is one of the most abundant bioactive biopolymer on earth. It is commercially extracted from seafood processing crustacean shell byproducts by harsh thermochemical treatments. The extraction conditions, the source and pretreatment of raw material significantly affect its quality and bioactivity. In this investigation response surface methodology (RSM) has been applied to optimize and evaluate the interaction of variables for extraction of high quality chitin from shrimp processing raw byproducts. Variables such as, concentration of HCl (%, v/v) 4.5 (for wet) and 4.9 (for dry), reaction time 3 h, solid liquid ratio of HCl (w/v) 1:5.5 (for wet) and 1:7.9 (for dry) with two treatments achieved >98 % demineralization of shrimp byproduct. Variables such as, concentration of NaOH 3.6 % (w/v), reaction time 2.5 h, temperature 69.0 ± 1 °C, solid liquid ratio of NaOH 7.4 (w/v) and two treatments accomplished >98 % deproteinization of demineralized byproducts. Significant (p ≤ 0.05-0.001) interactive effects were observed between different variables. Chitin obtained in these conditions had residual content (%, w/w) of ash <0.4 and protein <0.8 and the degree of N-acetylation was >93 % with purity of >98 %. In conclusion, the optimized conditions by RSM can be applied for large scale preparation of high quality chitin from raw shrimp byproduct.

Recent developments in chitosanase research and its biotechnological applications: a review

Chitosanases (EC 3.2.1.132) are glycosyl hydrolases that catalyse the endohydrolysis of β-1,4-glycosidic bonds of partially acetylated chitosan to release chitosan oligosaccharides (COS). Chitosanases are isolated, purified and characterised from different sources mainly from bacteria and fungi. Chitosanases have received much attention due to their wide range of applications including the preparation of bioactive COS and fungal protoplasts, as biocontrol agent against pathogenic fungi and insects, the bioconversion of chitinous bio waste associated with seafood processing, etc. Bioactive COS produced by the enzymatic hydrolysis of chitosan have finds numerous health benefits as well as other biological activities. This review summarizes the recent advances in chitosanases research, the enzyme production processes, characterization, genetic improvement and their applications.