The tale of a versatile enzyme: Molecular insights into keratinase for its industrial dissemination

Perspective on Agricultural Industrialization: Modification Strategies for Enhancing the Catalytic Capacity of Keratinase

Keratinases is a special hydrolytic enzyme produced by microorganisms, which has the ability to catalyze the degradation of keratin. Currently, keratinases show great potential for application in many agricultural and industrial fields, such as biofermented feed, leather tanning, hair removal, and fertilizer production. However, these potentials have not yet been fully unleashed on an industrial scale. This paper reviews the sources, properties, and catalytic mechanisms of keratinases. Strategies for the molecular modification of keratinases are summarized and discussed in terms of improving the substrate specificity, thermostability, and pH tolerance of keratinases. The modification strategies are also enriched by the introduction of immobilized enzymes and directed evolution. In addition, the selection of modification strategies when facing specific industrial applications is discussed and prospects are provided. We believe that this review serves as a reference for the future quest to extend the application of keratinases from the laboratory to industry.

Molecular strategies to enhance the keratinase gene expression and its potential implications in poultry feed industry

The tons of keratin waste are produced by the poultry and meat industry which is an insoluble and protein-rich material found in hair, feathers, wool, and some epidermal wastes. These waste products could be degraded and recycled to recover protein, which can save our environment. One of the potential strategy to achieve this target is use of microbial biotreatment which is more convenient, cost-effective, and environment-friendly by formulating hydrolysate complexes that could be administered as protein supplements, bioactive peptides, or animal feed ingredients. Keratin degradation shows great promise for long-term protein and amino acid recycling. According to the MEROPS database, known keratinolytic enzymes currently belong to at least 14 different protease families, including S1, S8, S9, S10, S16, M3, M4, M14, M16, M28, M32, M36, M38, and M55. In addition to exogenous attack (proteases from families S9, S10, M14, M28, M38, and M55), the various keratinolytic enzymes also function via endo-attack (proteases from families S1, S8, S16, M4, M16, and M36). Biotechnological methods have shown great promise for enhancing keratinase expression in different strains of microbes and different protein engineering techniques in genetically modified microbes such as bacteria and some fungi to enhance keratinase production and activity. Some microbes produce specific keratinolytic enzymes that can effectively degrade keratin substrates. Keratinases have been successfully used in the leather, textile, and pharmaceutical industries. However, the production and efficiency of existing enzymes need to be optimized before they can be used more widely in other processes, such as the cost-effective pretreatment of chicken waste. These can be improved more effectively by using various biotechnological applications which could serve as the best and novel approach for recycling and degrading biomass. This paper provides practical insights about molecular strategies to enhance keratinase expression to effectively utilize various poultry wastes like feathers and feed ingredients like soybean pulp. Furthermore, it describes the future implications of engineered keratinases for environment friendly utilization of wastes and crop byproducts for their better use in the poultry feed industry.

A comprehensive report on valorization of waste to single cell protein: strategies, challenges, and future prospects

The food insecurity due to a vertical increase in the global population urgently demands substantial advancements in the agricultural sector and to identify sustainable affordable sources of nutrition, particularly proteins. Single-cell protein (SCP) has been revealed as the dried biomass of microorganisms such as algae, yeast, and bacteria cultivated in a controlled environment. Production of SCP is a promising alternative to conventional protein sources like soy and meat, due to quicker production, minimal land requirement, and flexibility to various climatic conditions. In addition to protein production, it also contributes to waste management by converting it into food and feed for both human and animal consumption. This article provides an overview of SCP production, including its benefits, safety, acceptability, and cost, as well as limitations that constrains its maximum use. Furthermore, this review criticizes the downstream processing of SCP, encompassing cell wall disruption, removal of nucleic acid, harvesting of biomass, drying, packaging, storage, and transportation. The potential applications of SCP, such as in food and feed as well as in the production of bioplastics, emulsifiers, and as flavoring agents for baked food, soup, and salad, are also discussed.

Rational engineering S1' substrate binding pocket to enhance substrate specificity and catalytic activity of thermal-stable keratinase for efficient keratin degradation

This study reports the rational engineering of the S1' substrate-binding pocket of a thermally-stable keratinase from Pseudomonas aeruginosa 4-3 (4-3Ker) to improve substrate specificity to typical keratinase (K/C > 0.5) and catalytic activity without compromising thermal stability for efficient keratin degradation. Of 10 chosen mutation hotspots in the S1' substrate-binding pocket, the top three mutations M128R, A138V, and V142I showing the best catalytic activity and substrate specificity were identified. Their double and triple combinatorial mutants synergistically overcame limitations of single mutants, fabricating an excellent M128R/A138V/V142I triple mutant which displayed a 1.21-fold increase in keratin catalytic activity, 1.10-fold enhancement in keratin/casein activity ratio, and a 3.13 °C increase in half-inactivation temperature compared to 4-3Ker. Molecular dynamics simulations revealed enhanced flexibility of critical amino acid residues at the substrate access tunnel, improved global protein rigidity, and heightened hydrophobicity within the active site likely underpinned the increased catalytic activity and substrate specificity. Additionally, the triple mutant improved the feather degradation rate by 32.86 % over the wild-type, far exceeding commercial keratinase in substrate specificity and thermal stability. This study exemplified engineering a typical keratinase with enhanced substrate specificity, catalytic activity, and thermal stability from thermally-stable 4-3Ker, providing a more robust tool for feather degradation.

A scientific version of understanding "Why did the chickens cross the road"? - A guided journey through Bacillus spp. towards sustainable agriculture, circular economy and biofortification

The world, a famished planet with an overgrowing population, requires enormous food crops. This scenario compelled the farmers to use a high quantity of synthetic fertilizers for high food crop productivity. However, prolonged usage of chemical fertilizers results in severe adverse effects on soil and water quality. On the other hand, the growing population significantly consumes large quantities of poultry meats. Eventually, this produces a mammoth amount of poultry waste, chicken feathers. Owing to the protein value of the chicken feathers, these wastes are converted into protein hydrolysate and further extend their application as biostimulants for sustained agriculture. The protein profile of chicken feather protein hydrolysate (CFPH) produced through Bacillus spp. was the maximum compared to physical and chemical protein extraction methods. Several studies proved that the application of CFPH and active Bacillus spp. culture to soil and plants results in enhanced plant growth, phytochemical constituents, crop yield, soil nutrients, fertility, microbiome and resistance against diverse abiotic and biotic stresses. Overall, "CFPH - Jack of all trades" and "Bacillus spp. - an active camouflage to the surroundings where they applied showed profound and significant benefits to the plant growth under the most adverse conditions. In addition, Bacillus spp. coheres the biofortification process in plants through the breakdown of metals into metal ions that eventually increase the nutrient value of the food crops. However, detailed information on them is missing. This can be overcome by further real-world studies on rhizoengineering through a multi-omics approach and their interaction with plants. This review has explored the best possible and efficient strategy for managing chicken feather wastes into protein-rich CFPH through Bacillus spp. bioconversion and utilizing the CFPH and Bacillus spp. as biostimulants, biofertilizers, biopesticides and biofortificants. This paper is an excellent report on organic waste management, circular economy and sustainable agriculture research frontier.

Structural and enzymatic characterization of a novel metallo-serine keratinase KerJY-23

KerJY-23 was a novel keratinase from feather-degrading Ectobacillus sp. JY-23, but its enzymatic characterization and structure are still unclear. In this study, the KerJY-23 was obtained by heterologous expression in Escherichia coli BL21(DE3), and enzymatic properties indicated that KerJY-23 was optimal at 60 °C and pH 9.0 and could be promoted by divalent metal ions or reducing agents. Furthermore, KerJY-23 had a broad substrate specificity towards casein, soluble keratin, and expanded feather powder, but its in vitro degradation against chicken feathers required an additional reducing agent. Homology modeling indicated that KerJY-23 contained a highly conserved zinc-binding HELTH motif and a His-Asp-Ser catalytic triad that belonged to the typical characteristics of M4-family metallo-keratinase and serine-keratinase, respectively. Molecular docking revealed that KerJY-23 achieved a reinforced binding on feather keratin via abundant hydrogen bonding interactions. This work not only deepened understanding of the novel and interesting metallo-serine keratinase KerJY-23, but also provided a theoretical basis for realizing the efficient use of waste feather keratin.

Improvement in organic solvent resistance of keratinase BLk by directed evolution

Keratinase, a vital enzyme in hair degradation, requires enhanced stability for industrial applications in the harsh reaction environment used for keratin hydrolysis. Previous studies have focused on improving keratinase thermostability. In this study, directed evolution was applied to enhance the organic solvent stability of the keratinase BLk from Bacillus licheniformis. Three mutants were identified, exhibiting significant enhanced stability in various solvents, although no similar improvements were observed in terms of thermostability. The identified mutations were located on the enzyme surface. The half-lives of the D41A, A24E, and A24Q mutants increased by 47-, 63-, and 61-fold, respectively, in the presence of 50% (v/v) acetonitrile compared to that of the wild type (WT). Similarly, in the presence of 50% (v/v) acetone, the half-lives of these mutants increased by 22-, 27-, and 27-fold compared to that of the WT enzyme. Notably, the proteolytic activity of all the selected mutants was similar to that of the WT enzyme. Furthermore, molecular dynamics simulation was used to assess the possible reasons for enhanced solvent stability. These results suggest that heightened intramolecular interactions, such as hydrogen bonding and hydrophobic interactions, contribute to improved solvent tolerance. The mutants obtained in this study hold significant potential for industrial applications.

Effective biodegradation on chicken feather by the recombinant KerJY-23 Bacillus subtilis WB600: A synergistic process coupled by disulfide reductase and keratinase

Keratin wastes are abundantly available but rich in hard-degrading fibrous proteins, and the keratinase-producing microorganisms have gained significant attention due to their biodegradation ability against keratinous materials. In order to improve the degradation efficiency of feather keratins, the keratinase gene (kerJY-23) from our previously isolated feather-degrading Ectobacillus sp. JY-23 was overexpressed in Bacillus subtilis WB600 strain. The recombinant KerJY-23 strain degraded chicken feathers rapidly within 48 h, during which the activities of disulfide reductase and keratinase KerJY-23 were sharply increased, and the free amino acids especially the essential phenylalanine and tyrosine were significantly accumulated in feather hydrolysate. The results of structural characterizations including scanning electron microscopy, Fourier transform infrared spectrum, X-ray diffraction, and X-ray photoelectron spectroscopy, demonstrated that the feather microstructure together with the polypeptide bonds and SS bonds in feather keratins were attacked and destroyed by the recombinant KerJY-23 strain. Therefore, the recombinant KerJY-23 strain contributed to feather degradation through the synergistic action of the secreted disulfide reductase to break the SS bonds and keratinase (KerJY-23) to hydrolyze the polypeptide bonds in keratins. This study offers a new insight into the underlying mechanism of keratin degradation, and provides a potential recombinant strain for the valorization of keratin wastes.

Comprehensive insights into the mechanism of keratin degradation and exploitation of keratinase to enhance the bioaccessibility of soybean protein

Keratin is a recalcitrant protein and can be decomposed in nature. However, the mechanism of keratin degradation is still not well understood. In this study, Bacillus sp. 8A6 can completely degrade the feather in 20 h, which is an efficient keratin degrader reported so far. Comprehensive transcriptome analysis continuously tracks the metabolism of Bacillus sp. 8A6 throughout its growth in feather medium. It reveals for the first time how the strain can acquire nutrients and energy in an oligotrophic feather medium for proliferation in the early stage. Then, the degradation of the outer lipid layer of feather can expose the internal keratin structure for disulfide bonds reduction by sulfite from the newly identified sulfite metabolic pathway, disulfide reductases and iron uptake. The resulting weakened keratin has been further proposedly de-assembled by the S9 protease and hydrolyzed by synergistic effects of the endo, exo and oligo-proteases from S1, S8, M3, M14, M20, M24, M42, M84 and T3 families. Finally, bioaccessible peptides and amino acids are generated and transported for strain growth. The keratinase has been applied for soybean hydrolysis, which generates 2234 peptides and 559.93 mg/L17 amino acids. Therefore, the keratinases, inducing from the poultry waste, have great potential to be further applied for producing bioaccessible peptides and amino acids for feed industry.

Structure prediction, docking studies and molecular cloning of novel Pichia kudriavzevii YK46 metalloprotease (MetPr) for improvement of feather waste biodegradation

This study addresses the environmental risks associated with the accumulation of keratin waste from poultry, which is resistant to conventional protein degradation methods. To tackle this issue, microbial keratinases have emerged as promising tools for transforming resilient keratin materials into valuable products. We focus on the Metalloprotease (MetPr) gene isolated from novel Pichia kudriavzevii YK46, sequenced, and deposited in the NCBI GenBank database with the accession number OQ511281. The MetPr gene encodes a protein consisting of 557 amino acids and demonstrates a keratinase activity of 164.04 U/ml. The 3D structure of the protein was validated using Ramachandran's plot, revealing that 93% and 97.26% of the 557 residues were situated within the most favoured region for the MetPr proteins of template Pichia kudriavzevii strain 129 and Pichia kudriavzevii YK46, respectively. Computational analyses were employed to determine the binding affinities between the deduced protein and beta keratin. Molecular docking studies elucidated the optimal binding affinities between the metalloprotease (MetPr) and beta-keratin, yielding values of - 260.75 kcal/mol and - 257.02 kcal/mol for the template strains Pichia kudriavzevii strain 129 and Pichia kudriavzevii YK46, respectively. Subsequent molecular cloning and expression of the MetPr gene in E. coli DH5α led to a significantly higher keratinase activity of 281 ± 12.34 U/ml. These findings provide valuable insights into the potential of the MetPr gene and its encoded protein for keratin waste biotransformation, with implications for addressing environmental concerns related to keratinous waste accumulation.

Reducing Cellular Autolysis of Bacillus subtilis to Improve Keratinase Production

Bacillus subtilis has been shown to be an excellent expression host for keratinases due to its powerful secretion system. However, cellular autolysis limits its production capacity. Here, we selected seven genes with significantly upregulated transcript levels from 15 genes associated with cellular autolysis as knockout targets by qRT-PCR and constructed a total of 127 strains to reduce cellular autolysis. Among them, the biomass of B. subtilis BSΔXLPC-ker deficient in xpf, lytC, pcfA, and cwlC increased by 57%. This was confirmed by cell staining, green fluorescent protein imaging, and extracellular nucleic acid leakage assay. Keratinase activity was increased by 1.46-fold in the 5 L fermenter. In addition, the activities of nattokinase and subtilisin E were also increased by 1.50-fold and 1.43-fold, respectively, in the modified chassis cells, which further confirms the generalizability of the strategy. Thus, reducing cellular autolysis to increase the ability of B. subtilis to produce subtilisins is promising.

Fusion of Substrate-Binding Domains Enhances the Catalytic Capacity of Keratinases and Promotes Enzymatic Conversion of Feather Waste

The unique role of keratinases in keratin hydrolysis has garnered huge interest in the recovery of feather waste. However, owing to the high hydrophobicity of feather keratins, the catalytic capacity of keratinases for hydrolyzing feathers is typically low. In this study, we aimed to improve the keratinase feather hydrolysis efficiency by fusing a substrate-binding domain into the enzyme. We screened several carbohydrate-binding modules (CBMs) and linking peptides. We selected the most promising candidates to construct, clone, and express a fusion keratinase enzyme KerZ1/CBM-L8 with a feather hydrolysis efficiency of 7.8 × 10^-8 g/U. Compared with those of KerZ1, KerZ1/CBM-L8 has a feather hydrolysis efficiency that is 2.71 times higher, a k_cat value that is 179% higher, which translates to higher catalytic efficiency, and K_m and binding constant (K) values that are lower, which indicate a higher KerZ1/CBM-L8-keratin binding affinity. Moreover, the number of binding sites to the substrate (N), determined using isothermal titration calorimetry, was 24.1 times higher than that of KerZ1. Thus, the fusion of the substrate-binding domain improved the binding ability of the keratinase enzyme to the hydrophobic substrate, which improved its feather hydrolysis efficiency. Therefore, using the fusion keratinase would significantly improve the recovery of feather waste.

Optimized production of keratinolytic proteases from Bacillus tropicus LS27 and its application as a sustainable alternative for dehairing, destaining and metal recovery

The present study describes the isolation and characterization of Bacillus tropicus LS27 capable of keratinolytic protease production from Russell Market, Shivajinagar, Bangalore, Karnataka, with its diverse application. The ability of this strain to hydrolyze chicken feathers and skim milk was used to assess its keratinolytic and proteolytic properties. The strain identification was done using biochemical and molecular characterization using the 16S rRNA sequencing method. Further a sequential and systematic optimization of the factors affecting the keratinase production was done by initially sorting out the most influential factors (NaCl concentration, pH, inoculum level and incubation period in this study) through one factor at a time approach followed by central composite design based response surface methodology to enhance the keratinase production. Under optimized levels of NaCl (0.55 g/L), pH (7.35), inoculum level (5%) and incubation period (84 h), the keratinase production was enhanced from 41.62 U/mL to 401.67 ± 9.23 U/mL (9.65 fold increase) that corresponds to a feather degradation of 32.67 ± 1.36% was achieved. With regard to the cost effectiveness of application studies, the crude enzyme extracted from the optimized medium was tested for its potential dehairing, destaining and metal recovery properties. Complete dehairing was achieved within 48 h of treatment with crude enzyme without any visible damage to the collagen layer of goat skin. In destaining studies, combination of crude enzyme and detergent solution [1 mL detergent solution (5 mg/mL) and 1 mL crude enzyme] was found to be most effective in removing blood stains from cotton cloth. Silver recovery from used X-ray films was achieved within 6 min of treatment with crude enzyme maintained at 40 °C.

Development of a Growth-Dependent System to Regulate Cell Growth and Keratinase Production in B. subtilis

Keratinases specifically degrade insoluble keratin waste, thus contributing to environmental protection and sustainable biomass development. However, their industrial application is hindered by inefficient enzyme production and poor biomass generation. In this study, the heterologous expression of keratinase was found to have cytotoxicity and might block host cell growth due to its proteolytic property. To address this problem, an autoregulatory expression system based on quorum sensing was developed to synergistically regulate cell growth and keratinase production in Bacillus subtilis. The growth-dependent promoter P_aprE was chosen and shown to be effective in delaying keratinase production while promoting host cell proliferation. Copy number screening and core region mutations further balanced the two states. Carbon supplement optimization indicated that addition of 2% glucose facilitated biomass accumulation during the early stage of fermentation. Cell density increased to 15.6 (OD_600 nm) from 8 with keratinase activity raised to 4200 U·mL^-1 from 1162 U·mL^-1. Keratinase was then utilized in the bioconversion of feather waste to prepare soluble keratins, polypeptides, and amino acids. This study provides a powerful system for efficient production of keratinase and paves the way for keratin waste recycling.

Research progress on the degradation mechanism and modification of keratinase

Keratin is regarded as the main component of feathers and is difficult to be degraded by conventional proteases, leading to substantial abandonment. Keratinase is the only enzyme with the most formidable potential for degrading feathers. Although there have been in-depth studies in recent years, the large-scale application of keratinase is still associated with many problems. It is relatively challenging to find keratinase not only with high activity but could also meet the industrial application environment, so it is urgent to exploit keratinase with high acid and temperature resistance, strong activity, and low price. Therefore, researchers have been keen to explore the degradation mechanism of keratinases and the modification of existing keratinases for decades. This review critically introduces the basic properties and mechanism of keratinase, and focuses on the current situation of keratinase modification and the direction and strategy of its future application and modification. KEY POINTS: •The research status and mechanism of keratinase were reviewed. •The new direction of keratinase application and modification is discussed. •The existing modification methods and future modification strategies of keratinases are reviewed.

Multifarious revolutionary aspects of microbial keratinases: an efficient green technology for future generation with prospective applications

Since the dawn of century, tons of keratin bio-waste is generated by the poultry industry annually, and they end up causing environmental havoc. Keratins are highly flexible fibrous proteins which exist in α- and β- forms and provide mechanical strength and stability to structural appendages. The finding of broad-spectrum protease, keratinase, from thermophilic bacteria and fungi, has provided an eco-friendly solution to hydrolyze the peptide bonds in highly recalcitrant keratinous substances such as nails, feathers, claws, and horns into valuable amino acids. Microorganisms produce these proteolytic enzymes by techniques of solid-state and submerged fermentation. However, solid-state fermentation is considered as a yielding approach for the production of thermostable keratinases. This review prioritized the molecular and biochemical properties of microbial keratinases, and the role of keratinases in bringing prodigious impact for the sustainable progress of the economy. It also emphasizes on the current development in keratinase production with the focus to improve the biochemical properties related to enzyme's catalytic activity and stability, and production of mutant and cloned microbial strains to improve the yield of keratinases. Recently, multitude molecular approaches have been employed to enhance enzyme's productivity, activity, and thermostability which makes them suitable for pharmaceutical industry and for the production of animal feed, organic fertilizers, biogas, clearing of animal hides, and detergent formulation. Hence, it can be surmised that microbial keratinolytic enzymes are the conceivable candidates for numerous commercial and industrial applications.

Design of 5′-UTR to Enhance Keratinase Activity in Bacillus subtilis

Keratinase is an important industrial enzyme, but its application performance is limited by its low activity. A rational design of 5′-UTRs that increases translation efficiency is an important approach to enhance protein expression. Herein, we optimized the 5′-UTR of the recombinant keratinase KerZ1 expression element to enhance its secretory activity in Bacillus subtilis WB600 through Spacer design, RBS screening, and sequence simplification. First, the A/U content in Spacer was increased by the site-directed saturation mutation of G/C bases, and the activity of keratinase secreted by mutant strain B. subtilis WB600-SP was 7.94 times higher than that of KerZ1. Subsequently, the keratinase activity secreted by the mutant strain B. subtilis WB600-SP-R was further increased to 13.45 times that of KerZ1 based on the prediction of RBS translation efficiency and the multi-site saturation mutation screening. Finally, the keratinase activity secreted by the mutant strain B. subtilis WB600-SP-R-D reached 204.44 KU mL−1 by reducing the length of the 5′ end of the 5′-UTR, which was 19.70 times that of KerZ1. In a 5 L fermenter, the keratinase activity secreted by B. subtilis WB600-SP-R-D after 25 h fermentation was 797.05 KU mL−1, which indicated its high production intensity. Overall, the strategy of this study and the obtained keratinase mutants will provide a good reference for the expression regulation of keratinase and other industrial enzymes.

A combination of bioinformatics analysis and rational design strategies to enhance keratinase thermostability for efficient biodegradation of feathers

Keratinase has shown great significance and application potentials in the biodegradation and recycle of keratin waste due to its unique and efficient hydrolysis ability. However, the inherent instability of the enzyme limits its practical utilization. Herein, we obtained a thermostability-enhanced keratinase based on a combination of bioinformatics analysis and rational design strategies for the efficient biodegradation of feathers. A systematical in silico analysis combined with filtering of virtual libraries derived a smart library for experimental validation. Synergistic mutations around the highly flexible loop, the calcium binding site and the non-consensus amino acids generated a dominant mutant which increased the optimal temperature of keratinase from 40 °C to 60 °C, and the half-life at 60 °C was increased from 17.3 min to 66.1 min. The mutant could achieve more than 66% biodegradation of 50 g/L feathers to high-valued keratin product with a major molecular weight of 36 kDa. Collectively, this work provided a promising keratinase variant with enhanced thermostability for efficient conversion of keratin wastes to valuable products. It also generated a general strategy to facilitate enzyme thermostability design which is more targeted and predictable.

A Newly Isolated Strain Lysobacter brunescens YQ20 and Its Performance on Wool Waste Biodegradation

Wool keratin is difficult to degrade as comparing to feathers because of its tough secondary structure. In order to develop an approach for high-value utilization of wool fiber waste by keratinolytic microorganisms, which is produced from shearing, weaving, and industrial processing of wool, screening of wool-degrading bacterium with high degradation efficiency were performed in this study. To this end, Lysobacter brunescens YQ20 was identified and characterized. The optimized conditions for wool degradation were pH 9.0 and 37°C with 20% liquid volume of Erlenmeyer flask. After fermentation, 15 essential amino acids were detected when wool fiber waste was fermented. The total amino acids produced from 1% wool per hour were 13.7 mg/L. The concentration was 8.6-fold higher than that produced by the strain Stenotrophomonas maltophilia BBE11-1, which had previously been reported to have the highest wool-degrading capacity. Our study reports the first Lysobacter strain that exhibits efficient wool degradation and yields higher concentrations of amino acids than previously reported strains. Whole-genome sequencing indicated that there were 18 keratinase-like genes in the genome of YQ20, which exhibited a long evolutionary distance from those of Bacillus. Therefore, L. brunescens YQ20 may have applications in the environmentally friendly management of wool waste as fertilizer in agriculture.

Microbial proteases: ubiquitous enzymes with innumerable uses

Proteases are ubiquitous enzymes, having significant physiological roles in both synthesis and degradation. The use of microbial proteases in food fermentation is an age-old process, which is today being successfully employed in other industries with the advent of ‘omics’ era and innovations in genetic and protein engineering approaches. Proteases have found application in industries besides food, like leather, textiles, detergent, waste management, agriculture, animal husbandry, cosmetics, and pharmaceutics. With the rising demands and applications, researchers are exploring various approaches to discover, redesign, or artificially synthesize enzymes with better applicability in the industrial processes. These enzymes offer a sustainable and environmentally safer option, besides possessing economic and commercial value. Various bacterial and fungal proteases are already holding a commercially pivotal role in the industry. The current review summarizes the characteristics and types of proteases, microbial source, their current and prospective applications in various industries, and future challenges. Promoting these biocatalysts will prove significant in betterment of the modern world.

Closing the Loop with Keratin-Rich Fibrous Materials

One of the agro-industry's side streams that is widely met is the-keratin rich fibrous material that is becoming a waste product without valorization. Its management as a waste is costly, as the incineration of this type of waste constitutes high environmental concern. Considering these facts, the keratin-rich waste can be considered as a treasure for the producers interested in the valorization of such slowly-biodegradable by-products. As keratin is a protein that needs harsh conditions for its degradation, and that in most of the cases its constitutive amino acids are destroyed, we review new extraction methods that are eco-friendly and cost-effective. The chemical and enzymatic extractions of keratin are compared and the optimization of the extraction conditions at the lab scale is considered. In this study, there are also considered the potential applications of the extracted keratin as well as the reuse of the by-products obtained during the extraction processes.

Effect of Agitation and Aeration on Keratinase Production in Bioreactors Using Bioprocess Engineering Aspects

Streptomyces sp. 2M21 was evaluated for keratinase production in bioreactors using chicken feathers. Firstly, optimization of bioengineering parameters (agitation and aeration rates) using Response Surface Methodology was carried out in 2 L bioreactors. Optimized conditions identified by the modified quadratic model were verified as 150 rpm and 1 vvm experimentally corresponding to 351 U/ml of keratinase activity. Moreover, scaling up sequentially to 20 L bioreactors was implemented using constant impeller tip speed and constant mass transfer coefficient as key scale-up parameters. The keratinase activity in 5, 10 and 20 L bioreactors showed similar results with the one of shake flasks (412 U/ml) and 2 L bioreactors (351 U/ml)with respect to the keratinase activity values of 336, 385 and 344 U/ml, respectively. The results suggest keratinase production by evaluating chicken feathers in commercial level. Furthermore, this study has potential to contribute industrial scale production of keratinase by Streptomyces sp. 2M21 using the proposed bioreactor conditions.

Key Challenges of Microbial Degradation of Keratinous Wastes

Feather is the main waste of poultry industries and constitutes of 90% keratin. Wastes composed of keratin are insoluble and recalcitrant to degradation using conventional decomposing methods. Microbial degradation for keratinous wastes is a promising approach for being eco-friendly and economically. However, due to insolubility of keratinous waste, it has several challenges in upstream and downstream processes such as culture medium optimization, designing of bioreactor, bioreaction/flow type, bioreactor configurations considering mass and heat transfer limitations, rheology derived problems, monitoring of microbial activity, choosing of the right scale-up parameter and purification. In this study, the challenges for keratin degradation processes were discussed with the aim of opening new opportunities for keratinous waste treatments in industrial level.