Microbial enzymes catalyzing keratin degradation: Classification, structure, function

Keratinase and its diverse applications

Keratinase is a proteolytic enzyme specialized in the degradation of keratin-rich materials and has garnered significant attention for its potential in various biotechnological applications. This review provides an overview of keratinase, focusing on its structure, classification, function, biochemical properties, mechanisms of action and diverse applications. Keratinase plays an important role in bioremediation and stands out prominently, as it facilitates the eco-friendly degradation of keratinaceous waste materials addressing environmental concerns by reducing pollution and waste accumulation. Moreover, in the textile industry, keratinase plays a pivotal role in bio-pretreatment processes, enhancing the dyeing and finishing properties of animal fibers such as wool and silk. Beyond textiles, this enzyme contributes significantly to animal feed production by hydrolyzing keratin-rich byproducts into digestible components, thereby fostering the creation of high-protein feeds. Its impact extends to the cosmetic and pharmaceutical realms, where keratinase finds use in skincare formulations and in treating certain dermatological conditions owing to its ability to modify and break down keratin structures. By assisting in the removal of dead tissue, it demonstrates potential in biological applications for wound healing. Additionally, the challenges and future perspectives on the commercial scalability of keratinase production and its integration into various sectors are discussed.

Bioconversion of Feather and Production of Alkaline Protease for Detergent and Dehairing Applications

Annually, the poultry industry releases millions of tons of feather waste into the environment. With a protein content of 91%, feather offers huge potential to serve as an animal feed supplement. However, keratin, the main protein component of feather, is highly resistant to hydrolysis by animal and plant proteases. The use of physicochemical methods to hydrolyze feather, in addition to being expensive, causes decomposition of some amino acids. Thus, microbial bioconversion of feather offers an attractive option for the production of useful products. In this study, an alkaliphilic feather-degrading strain, Bacillus pseudofirmus BCC026, was isolated from the Makgadikgadi salt pan in Botswana. When grown in liquid culture containing feather as the sole source of nitrogen, it resulted in complete solubilization within 48 to 72 h. The organism also produced an alkaline protease, soluble proteins, and peptides/amino acids into the culture medium. The enzyme showed optimum activity in the pH range of 7.5-10.5 and at 70 °C. It was also active and stable in commercial detergents and resulted in complete removal of stain from cotton fabrics. The enzyme was also effective in removing hair from goatskin, indicating its potential for dehairing application. Microbial growth substrates are known to account for a significant proportion of the production cost of industrial enzymes. Since protease BCC026 was produced using feather, a cheap and readily available resource, enzyme production cost could be significantly reduced. Moreover, after enzyme recovery, the soluble proteins and peptides/amino acids in the filtrate could be used for different applications.

Comparative analysis of pre-treatment strategies and bacterial strain efficiency for improvement of feather hydrolysis

BACKGROUND

Feathers are a major by-product of the poultry industry, which poses an environmental challenge due to the recalcitrant structure of keratin, making them resistant to degradation. Traditional methods of feather handling, like conversion to feather meal, are energy-intensive and have limited efficiency. Biotechnological approaches, particularly microbial hydrolysis, offer a novel and more sustainable alternative for keratin degradation. This study evaluated feather hydrolysis by two bacterial strains, newly characterized cold-adapted Arthrobacter oryzae (BIM B-1663) and Bacillus licheniformis (CCM 2145T), known as a keratin degrader, under various feather pre-treatment conditions, including washing, autoclaving, drying, and grinding.

RESULTS

Both bacterial strains were able to degrade pretreated feathers with a degradation efficiency of 75 to 90%, resulting in high ratios of nitrogen to carbon in the hydrolysates. B. licheniformis confirmed its enzymatic capabilities with high levels of general and specific protease activity and furthermore presented enriched amounts of amino acids of industrial interest. A. oryzae showed a much higher keratinase/protease activity ratio, demonstrating high specificity and efficiency of its enzymes. Autoclaving emerged as the most important determinant of microbial degradation efficiency and influenced the composition (peptide pattern, amino acid content, and chemical composition assessed through FTIR) of the resulting hydrolysates. Feather drying, although not improving microbial degradation efficiencies, had a considerable impact on hydrolysate composition.

CONCLUSIONS

The results show that both tested bacterial strains can efficiently degrade autoclaved feathers but use distinct enzymatic strategies to do so. Enriched profiles in amino acids and high nitrogen content in the hydrolysates also advocate for the benefits of microbial feather hydrolysis over an enzymatic one. To the authors' knowledge this study is the first to report a comprehensive evaluation of the impact of various feather pre-treatment methods on the efficiency of subsequent microbial feather hydrolysis and is the first one to report enrichment in phenylalanine, lysine, and tyrosine secreted by B. licheniformis.

Recombinant keratin: Comprehensive review of synthesis, hierarchical assembly, properties, and applications

Keratin has gained attention for its remarkable mechanical properties, thermal stability, and beneficial biological properties, such as promoting hemostasis and wound healing. Traditionally, keratin has been extracted from natural sources, including human hair, wool, and feathers, and processed into biomaterials, including films, hydrogels, and nanoparticles, primarily for biomedical applications. However, extraction methods often result in heterogeneous keratin mixtures with residual impurities and structural degradation due to harsh purification conditions, complicating efforts to understand how specific keratins and their hierarchical assemblies contribute to desired material properties. Recombinant keratin technology addresses these challenges by enabling the synthesis of individual keratin types with high purity and batch-to-batch consistency. These advancements facilitate studies on how individual and combined keratins at various assembly stagesfrom molecular components and heterodimers to intermediate filaments (IFs) and IF networksimpact material properties. Moreover, this technology allows for precise genetic modifications, potentially leading to engineered keratin variants with tailored characteristics for targeted applications. Despite these advantages, translating recombinant keratin into practical applications requires overcoming key manufacturing challenges, such as optimizing large-scale production and improving purification efficiency. This review presents the current state of recombinant keratin research by highlighting its advancements and exploring current biomaterial applications. While its applications remain limited compared to extracted keratin at this early stage, its potential offers future opportunities for extending its use in advanced material design and beyond biomedical fields. STATEMENT OF SIGNIFICANCE: Keratin and keratinized structures provide essential protection to tissues against mechanical stress and environmental damage, serving as foundational elements across diverse biological systems. This review discusses advancements in recombinant keratin technology, enabling high-purity, reproducible synthesis with controlled composition modifications that effectively overcome the limitations of traditional extraction methods. The innovations deepen our understanding of hierarchical assembly in keratin structures across various length scales, along with their reinforcing mechanisms and mechanical and biofunctional properties. These insights lay the groundwork for biomaterials tailored to regenerative medicine, wound healing, and other biomedical applications. By focusing on the unique capabilities of recombinant keratin, this review offers a valuable resource for future advancements in high-performance biomaterials across biomedical and biotechnological fields.

Characterization of keratinase from Chryseobacterium camelliae Dolsongi-HT1 and efficacy on skin exfoliation

Keratin is the outermost layer that protects our skin and has an appropriate turnover cycle. With age, the keratin turnover cycle begins to dysfunction. To overcome this issue, we artificially remove dead skin cells. In this study, we attempted to screen enzymes that could be useful in the cosmetics industry to develop enzymes suitable for the enzyme-based method, a mild exfoliation method that does not damage the skin. Chryseobacterium camelliae Dolsongi-HT1 with keratinolytic activity was isolated from green tea leaves (sourced from the Dolsongi tea garden, Jeju Island). The keratinolytic activity of C. camelliae Dolsongi-HT1 was detected in the culture media, indicating that the target keratinolytic enzyme is a secreted protein. Keratinolytic activity was demonstrated using forearm skin keratin and reconstituted human skin models. The enzyme from C. camelliae Dolsng-HT1 (HT1) could efficiently decompose human skin keratin. Moreover, experiments using the reconstituted human skin model demonstrated that HT1 is efficient in exfoliating the outermost stratum corneum. Compared with the popularly used chemical exfoliation method, enzymatic exfoliation using HT1 was less abrasive and did not damage the epidermal layer. Keratinolytic enzyme was identified using protein purification and mass spectrometry. The identified enzyme (iHT1) was expressed in the Bacillus subtilis RIK 1285 secretory protein expression system. The iHT1 enzyme showed high activity over a wide temperature range (30-60 °C), with the highest activity at 30 °C. The optimum pH for the activity of iHT was pH8.

Current Understanding of Feather Keratin and Keratinase and Their Applications in Biotechnology

The food industry generates substantial keratin waste, particularly chicken feathers, which are rich in amino acids and essential nutrients. However, the insolubility of keratin presents a significant challenge to its conversion. Keratinase, an enzyme produced by certain fungi and bacteria, offers a promising solution by degrading feather keratin into amino acids and soluble proteins. Among these, bacterial keratinase is notable for its superior stability and activity, although its production remains constrained, necessitating continued research to identify efficient microbial strains. Keratin-derived hydrolyzates, recognized for their biological and immunological properties, have garnered significant research interest. This review examines the structural characteristics of chicken feather keratin, its resistance to conventional proteases, and advances in keratinase production and purification techniques. Additionally, the keratin degradation mechanism and the adoption of environmentally friendly technologies for managing feather waste are explored. Finally, the review highlights the potential applications of keratinase across diverse industries, including animal feed and cosmetics.

Transcriptomic and proteomic insights into feather keratin degradation by Fervidobacterium

Keratin, one of the most recalcitrant and abundant proteins on Earth, constitutes a challenging and underutilized material for the poultry industry. Although it resists degradation by most commonly available enzymes, natural breakdown occurs through the action of certain fungi and bacteria. This process remains poorly understood, and only a few thermophilic and anaerobic bacteria are known to effectively degrade keratin. Some members of the genus Fervidobacterium have been demonstrated to be effective at degrading feather keratin under high temperatures and anoxic conditions. However, a comprehensive evaluation of their keratinolytic capabilities remains lacking, leaving their potential largely underexplored. In this study, we assessed the keratinolytic activity of all available Fervidobacterium strains. Six strains were active against this recalcitrant substrate, namely Fervidobacterium changbaicum CBS-1T, Fervidobacterium islandicum H-21T, Fervidobacterium pennivorans T, Fervidobacterium pennivorans DSM9078T, Fervidobacterium sp. GSH, and Fervidobacterium sp. 21710. These bacteria were used in a comparative proteomics analysis, grown with either glucose or chicken feathers as the sole carbon source. Similarly, the three most efficient strains, Fervidobacterium pennivorans T, Fervidobacterium sp. GSH, and Fervidobacterium islandicum H-21T underwent an in-depth comparative transcriptomics analysis. Among the numerous upregulated proteins and overexpressed genes identified when comparing feather-grown to glucose-grown cells, oxidoreductases and peptidases are key enzymes in the degradation process, suggesting their potential application in enzymatic keratinolytic cocktails for degrading feather keratin.

Keratinous bioresources: their generation, microbial degradation, and value enhancement for biotechnological applications

Keratin is an important bioresource primarily found in feathers, hair, wool, nails, claws, hooves, horns, and beaks. These crucial protein sources are utilized in many ways for diverse applications. The peptides of keratin develop hierarchical complexity, which leads to the formation of these recalcitrant biomasses. Therefore, microbial breakdown of keratin is a complex process and involves important proteolytic enzymes and inorganic factors. Disulfide bond reduction is the key step in keratin degradation that is mainly facilitated by disulfide-reducing agents or disulfide reductases. Notably, α- and β-keratinous substrates exhibit different structural features; as a result, their disintegration processes make a diversity among keratinous biomass. Various studies have suggested that pretreatment can improve degradation yield following microbial processes. Keratin hydrolysates have been investigated for various uses that contribute to mitigating the environmental impact of these solid wastes. Furthermore, keratin peptides possess bioactive properties, including antioxidant, cytoprotective, and anticancer effects, making them potential candidates for biomedical and nutritional sectors. Microbial keratinases are known for a wide range of substrate specificity that significantly contributes to areas like prion decontamination, carcass processing, antimicrobial functions, and skin exfoliation. This review aims to examine keratin bioresources, their structure, and microbial mechanisms for keratin degradation, along with current insights and future applications of keratin hydrolysates and keratinases.

An update on thermostable keratinases for protein engineering against feather pollutants

Every year, the poultry business worldwide produces at least 8.5 billion tonnes of chicken feathers, making it one of the major landfill pollutants in the world. Biodegradation and recycling of native feathers is difficult due to the presence of numerous disulfide linkages in the feather's major constituent, keratin. Denaturation of such recalcitrant protein is thermodynamically favored at high temperatures. Therefore, the lookout for the enzymes that degrade keratin (keratinases) from thermophilic bacteria resulted in the identification of thermostable enzymes favoring feather degradation at high temperatures. This review presents a comprehensive analysis of the biochemical properties and structural attributes of thermostable keratinases, emphasizing their catalytic mechanisms, stability at high temperatures, and substrate specificity. Our exploration of structural features enables us to understand the molecular architecture of these enzymes for protein engineering that might enhance the keratinolytic activity and thermostability further. As the field of protein engineering advances, there exists a pressing requirement for integration of structural data with pragmatic engineering applications. Our review addresses for the first time the detailed structural aspects of thermostable bacterial keratinolytic enzymes that will facilitate the development of modified keratinases through protein engineering for a broad range of industrial applications, such as in the production of biofuels, leather processing, and waste management. KEYPOINTS: • Efficient eco-friendly bioremediation of feather landfill pollutant using thermophilic keratinases. • Detailed structural and biochemical aspects of different thermophilic bacterial keratinases. • Combinations of thermostable keratinases for the enhanced feather degradation process.

Biochemical characterization and molecular docking of a novel alkaline-stable keratinase from Amycolatopsis sp. BJA-103

Amycolatopsis sp. BJA-103 was isolated for its exceptional feather-degradation capability, leading to the purification, cloning, and heterologous expression of the keratinase enzyme, KER0199. Sequence analysis places KER0199 within the S8 protease family, revealing <60 % sequence similarity to known proteases. The recombinant KER0199-His6 demonstrates a broad substrate range, along with remarkable thermostability and alkaline stability, exhibiting optimal activity at pH 11.0 and 60 °C, despite the absence of cysteine residues essential for disulfide bonding. Structural modeling reveals a predominantly negatively charged surface and a flat, low-electrostatic-potential substrate-binding pocket. Substrate-binding models, predicted using AlphaFold3 and molecular dynamics simulations, indicate that substrates such as casein, chicken feather β-keratin P2450, and hemoglobin bind to this pocket, forming anti-parallel β-sheets with residues G97 to G99 and establishing extensive hydrogen bonds with key residues near the enzyme's active site. These findings suggest that AlphaFold-based substrate binding predictions, combined with an analysis of intermolecular forces, provide a valuable tool for assisting in the elucidation of enzyme specificity and substrate recognition. KER0199, the first characterized S8 family keratinase from the Amycolatopsis genus, shows great potential for industrial applications.

Tenuifilum osseticum sp. nov., a novel thermophilic hydrolytic bacterium within the Tenuifilaceae isolated from a North Ossetian thermal spring, and emended description of the genus Tenuifilum

A novel anaerobic moderately thermophilic bacterium, strain 4138-strT, was isolated from a thermal spring of North Ossetia (Russian Federation). Gram-negative cells were non-sporeforming, straight or curved filamentous rods, occasionally forming rosettes. The strain grew at 30-55 °C, pH range of 6.1-8.7, NaCl range of 0-4 %, with an optimum at 50 °C, pH 7.1-7.5 and 0.2-0.4 % NaCl. It was a chemoorganoheterotroph, growing on simple sugars (glucose, maltose, cellobiose, etc.) and carbohydrates (starch, pullulan, laminarin, xylan, lichenan, curdlan, pachyman) or proteinaceous substrates (peptone, tryptone, gelatin, casein). Sulfur was used as electron acceptor. Major products of glucose fermentation were acetate, hydrogen, and carbon dioxide. Major cellular fatty acids were iso-C15:0 and anteiso-C15:0. The quinone was MK-7. The size of the whole genome of strain 4138-strT was 3.275 Mbp; DNA G + C content was 42.1 %. Genome analysis allowed to identify genes encoding carbohydrate-active enzymes and extracellular proteases. In addition, central metabolism and fermentation pathways of strain 4138-strT were reconstructed. According to both phylogenetic analyses, based on 16S rRNA gene sequences and conserved protein sequences, as well as genome-based comparisons, strain 4138-strT formed a species-level lineage within Tenuifilum genus of Tenuifilaceae family (phylum Bacteroidota). Here we propose a novel species Tenuifilum osseticum sp. nov. with type strain 4138-strT(=KCTC 25386T = VKM B-3628T = UQM 41477T).

Enzymatic processes for animal hide/skin collagen fiber purification processing: Recent progress, challenges and recommendations

Collagen fiber purification is the most important pretreatment process in the recycling of animal hide/skin, by-products of meat production, and can be utilized to produce value-added materials. Traditional animal hide/skin resource utilization technologies face serious challenges in the aspect of production efficiency and environmental sustainability. Enzymatic collagen fiber purification processing is thought to be one of the most promising technologies that can minimize the use of chemicals and energy, reduce CO2-eq emissions, and achieve sustainable development of animal hide/skin reutilization. However, enzymatic processes have not been well accepted for industrial-scale applications in factories so far. In this review, recent progress and challenges of enzymatic collagen fiber purification processing were comprehensively overviewed in the aspect of the key mechanisms and technologies of enzyme application. Recommendations for the direction of enzyme selection and development were put forward, which is expected to pave the way for the industrial-scale application of enzymes in animal hide/skin collagen fiber purification processing.

Upcycling of Enzymatically Recovered Amino Acids from Textile Waste Blends: Approaches for Production of Valuable Second-Generation Bioproducts

Tremendous quantities of textile waste generated and primarily landfilled annually represent a huge risk of contaminating the environment, together with loss of valuable resources. Especially, blended fabrics further pose a challenge for recycling and valorization strategies, while enzymatic hydrolysis offers a highly specific and environmentally friendly solution. In this study, we demonstrate that proteases specifically hydrolyze the wool components in blends with polyester, allowing recovery of pure polyester fibers as well as amino acids and peptides as platform molecules for further valorization. Recovered amino acids and peptides were successfully used as a nitrogen source for cultivation of Chlorella vulgaris and Rhodotorula mucilaginosa for the production of valuable biomolecules including pigments and lipids. Here, 11.3 mg/gCDW chlorophyll and 47% lipid content were obtained from algal biomass, while 1.1 mg/gCDW carotenoids and 35% lipids content were reached from the yeast grown on wool hydrolysate as the sole nitrogen source. These could be applied as natural dyes for textile applications or as biofuels to replace toxic synthetic compounds and fossil resources, respectively. The presented concept demonstrates feasibility of enzymatic recovery and microbial valorization of components of blended textile waste to support the development toward a circular bioeconomy.

Unlocking the Potential of Keratin: A Comprehensive Exploration from Extraction and Structural Properties to Cross-Disciplinary Applications

The rapid expansion of the livestock and poultry industry has led to a considerable increase in slaughter byproducts; however, exploring their potential applications still needs to be improved. These underutilized byproducts, which include nails, hides, skins, and bones, represent a significant loss of valuable biological resources. Among these materials, keratin has garnered considerable attention due to its unique properties as a natural biopolymer. Keratin exhibits outstanding mechanical properties and biocompatibility and has attracted increasing attention for its recovery and conversion into relevant application materials. However, natural keratin typically has a high sulfur content, complex 3D structure, and abundant hydrogen and disulfide bonds, which cause challenges in application. Current extraction for keratin includes physical, chemical, biological, and hybrid approaches. Combining multiple methods synergistically enhances protein extraction efficiency and purity, and facilitates the exploration of structure and functional properties. This review encompasses the structural characteristics, properties, extraction methods, and research progress related to keratin. The preparation and application of keratin composite materials in different forms, such as fibers, films, hydrogels, and scaffolds, are illustrated. Applications in several fields, including biomedicine, flexible electronic components, environmental materials and food packaging are discussed. Hopefully, this paper will provide a comprehensive understanding and guidance for further development and application of keratin materials.

Targeted Adherence and Enhanced Degradation of Feather Keratins by a Novel Prepeptidase C-Terminal Domain-Fused Keratinase

Keratinases are valuable enzymes for converting feather keratin waste into bioactive products but often suffer from poor substrate specificity and low catalytic efficiency. This study reported the creating of a novel keratinase with targeted adherence and specific degradation on feather keratins by fusing prepeptidase C-Terminal (PPC) domain. A PPC domain of metalloprotease E423 specifically adsorbed feather keratins by hydrogen bonds and hydrophobic interactions in a time- and temperature-dependent manner. Stepwise N-/C-terminal truncations disclosed the essential core sequence composed of 21 amino acid residues determining the keratin-targeted adherence. Fusion of the core fragment with a flexible linker (GGGGS)1 achieved the optimal secretion, and improved the catalytic efficiency of a representative keratinase 4-3Ker-MAV by 0.97-fold. Moreover, the feather degradation rate increased from 65 to 82%, representing the highest reported performance for a keratinase. This PPC-fusion strategy opens new horizons in enzyme engineering, promising not only to revolutionize keratin waste valorization but also to inspire the design of substrate-specific biocatalysts across diverse industrial applications.

Innovative bioinks for 3D bioprinting: Exploring technological potential and regulatory challenges

The field of three dimensional (3D) bioprinting has witnessed significant advancements, with bioinks playing a crucial role in enabling the fabrication of complex tissue constructs. This review explores the innovative bioinks that are currently shaping the future of 3D bioprinting, focusing on their composition, functionality, and potential for tissue engineering, drug delivery, and regenerative medicine. The development of bioinks, incorporating natural and synthetic materials, offers unprecedented opportunities for personalized medicine. However, the rapid technological progress raises regulatory challenges regarding safety, standardization, and long-term biocompatibility. This paper addresses these challenges, examining the current regulatory frameworks and the need for updated guidelines to ensure patient safety and product efficacy. By highlighting both the technological potential and regulatory hurdles, this review offers a comprehensive overview of the future landscape of bioinks in bioprinting, emphasizing the necessity for cross-disciplinary collaboration between scientists, clinicians, and regulatory bodies to achieve successful clinical applications.

Comparative genomics of Fervidobacterium: a new phylogenomic landscape of these wide-spread thermophilic anaerobes

BACKGROUND

Fervidobacterium is a genus of thermophilic anaerobic Gram-negative rod-shaped bacteria belonging to the phylum Thermotogota. They can grow through fermentation on a wide range of sugars and protein-rich substrates. Some can also break down feather keratin, which has significant biotechnological potential. Fervidobacteria genomes have undergone several horizontal gene transfer events, sharing DNA with unrelated microbial taxa. Despite increasing biotechnological and evolutionary interest in this genus, only seven species have been described to date. Here, we present and describe six new and complete Fervidobacterium genomes, including the type strains Fervidobacterium gondwanense CBS-1 T, F. islandicum H-21 T and F. thailandense FC2004T, one novel isolate from Georgia (strain GSH) and two strains (DSM 21710 and DSM 13770) that have not been previously described along with an evolutionary and phylogenomic analysis of the genus.

RESULTS

The complete genomes were around 2 Mb with approximately 2,000 CDS identified and annotated in each of them and a G + C content ranging from 38.9 mol% to 45.8 mol%. Phylogenomic comparisons of all currently available Fervidobacterium genomes, including OrthoANI and TYGS analyses, as well as a phylogenetic analysis based on the 16S rRNA gene, identified six species and nine subspecies clusters across the genus, with a consistent topology and a distant and separately branching species, Fervidobacterium thailandense. F. thailandense harbored the highest number of transposases, CRISPR clusters, pseudo genes and horizontally transferred regions The pan genome of the genus showed that 44% of the genes belong to the cloud pangenome, with most of the singletons found also in F. thailandense.

CONCLUSIONS

The additional genome sequences described in this work and the comparison with all available Fervidobacterium genome sequences provided new insights into the evolutionary history of this genus and supported a phylogenetic reclassification. The phylogenomic results from OrthoANI and TYGS analyses revealed that F. riparium and F. gondwanense belong to the same genome species, and includes Fervidobacterium sp. 13770, while "F. pennivorans" strain DYC belongs to a separate genome species, whereas Fervidobacterium sp. 21710 and Fervidobacterium sp. GSH within the Fervidobacterium pennivorans clade represent two subspecies. F. changbaicum is reclassified as F. islandicum.

In-situ production of amino acid-rich monoammonium phosphate from chicken feathers provides superior efficacy compared to physical blending

A large amount of feather waste is discarded annually, leading to severe environmental pollution problems. Meanwhile, to improve the utilization efficiency of phosphate fertilizers, this study utilized wet-process phosphoric acid (WPPA) to hydrolyze feathers in-situ, producing ammonium amino acid phosphate (AAMAP), and set up physically mixed ammonium phosphate (ARMAP) as a control. The application effects of AAMAP and ARMAP produced under different conditions on bok choy growth were investigated. The results showed that AAMAP consistently outperformed ARMAP in promoting yield, with fresh weight and dry weight increases ranging from 1.38 % to 26.06 % and 5.69 % to 20.67 %, respectively. Among all treatments, the AAMAP (150 g/L-3) group was the most effective, increasing fresh weight and dry weight by 37.13 % and 46.13 % compared to the blank control group. Analysis revealed that the superior application effect of AAMAP was attributed to the elimination of the water-insoluble NH4MgPO4·H2O crystals due to amino acid chelation, leading to improved phosphorus and magnesium utilization, as well as the formation of phosphoesters. Furthermore, economic analysis showed that the addition cost of AAMAP was only 28.52 % of ARMAP. This method of utilizing WPPA to hydrolyze feathers in-situ for AAMAP production is an economical and effective approach to treat feather waste and enhance the utilization efficiency of phosphate fertilizers.

Biodegradation of different keratin waste by newly isolated thermophilic Brevibacillus gelatini LD5: Insights into the degradation mechanism based on genomic analysis and keratin structural changes

Keratin is an abundant environmental solid waste. This work isolated a thermophilic strain from a hot spring with efficient keratinolytic ability. The strain was identified and named as Brevibacillus gelatini LD5 based on whole-genome sequence analysis. The strain has genes related to keratin degradation, including disulfide reduction, keratin denaturation, protein proteolysis and metabolism of amino acids. The keratinases derived from this strain were the endo-acting M4, M16 and S8 proteases, exo-acting S9 protease and oligo-acting M3 and M32 peptidases via Conserved Unique Peptide Patterns (CUPP) prediction. The LD5 can degrade different keratin biomass, e.g. chicken feathers (CF), goose feathers (GF), pig hair (PH), cat hair (CH) and dog hair (DH). The degradation rate of CF was 62.45 % after 24-h fermentation. The hydrolysates from different keratin biomass have all shown keratinolytic activity, antioxidant and antiradical activities. The random structure of keratin was easier to be degraded by LD5 from Fourier transform infrared (FT-IR) analysis. The optimum temperature-pH conditions of the keratinases were 79.8 °C and pH 7.5, and thermal stability of the keratinases reached 71.5 min at 70 °C. These results demonstrated that B. gelatini LD5 has potential application in keratin wastes biodegradation and thermal stable keratinase production.

Applications and environmental impact of biodegradable polymers in textile industry: A review

With the increasing global population, the disposal of waste has risen, especially over the last century. The Environmental Protection Agency (EPA) reported that 11 million tons of textile-related waste were landfilled in the USA in 2018, and this amount is projected to increase to 4.5 billion tons by 2040. Bio-based polymers have gained attention due to their remarkable properties. The most important biodegradable polymers include PLA, PHA, PHB, PCL, PBS, bamboo fibers, and banana fibers. Global biopolymer production capacity is expected to rise significantly, from around 2.18 million tons in 2023 to approximately 7.43 million tons by 2028. In the textile industry, the linear waste model presents numerous challenges, such as environmental damage and resource shortages. Shifting from a linear to a circular economy is essential to address these issues. Reducing, reusing, and recycling are the three key actions and strategies that form the foundation of the circular economy. This paper presents the current state of knowledge and technological advancements in biodegradable polymers in the textile industry, along with their products and applications. The study explores the cost-effectiveness, limitations, opportunities, and advancements in their manufacturing technologies. Biodegradable polymers in the textile sector are regarded as green alternatives to non-biodegradable polymers.

Keratinous and corneous-based products towards circular bioeconomy: A research review

Keratins and corneous proteins are key components of biomaterials used in a wide range of applications and are potential substitutes for petrochemical-based products. Horns, hooves, feathers, claws, and similar animal tissues are abundant sources of α-keratin and corneous β-proteins, which are by-products of the food industry. Their close association with the meat industry raises environmental and ethical concerns regarding their disposal. To promote an eco-friendly and circular use of these materials in novel applications, efforts have focused on recovering these residues to develop sustainable, non-animal-related, affordable, and scalable procedures. Here, we review and examine biotechnological methods for extracting and expressing α-keratins and corneous β-proteins in microorganisms. This review highlights consolidated research trends in biomaterials, medical devices, food supplements, and packaging, demonstrating the keratin industry's potential to create innovative value-added products. Additionally, it analyzes the state of the art of related intellectual property and market size to underscore the potential within a circular bioeconomic model.

Unraveling dynamics and interactions of core microorganisms in the biodegradation of keratin-based feather wastes

Waste feathers, abundant byproducts of the poultry industry, pose significant environmental challenges. Although microbial degradation has been investigated, the core microorganisms and their interactions remain underexplored. This study examined microbial community dynamics during feather degradation, using diverse feather sources and under varying temperatures. Significant divergences were observed in bacterial communities, with Firmicutes, Actinobacteria, and Acidobacteriota (56.65%, 18.13%, and 11.14%) as dominant phyla. A core microbial consortium of 51 taxa was identified, with 8 core genera from the Bacilli class, significantly enriched during degradation. Higher temperature (50 °C) accelerated degradation. Dynamics patterns showed the enrichment of and depletion of some strains. Functional prediction highlighted the mechanisms for keratin biodegradation. This study identified core microorganisms and enzymes during keratin degradation, providing evidence to microbial treatment of keratin-based waste to reduce agricultural pollution.

High keratinase and other types of hydrolase activity of the new strain of Bacillus paralicheniformis

Keratinases, a subclass of proteases, are used to degrade keratin thereby forming peptones and free amino acids. Bacillus paralicheniformis strain T7 was isolated from soil and exhibited high keratinase, protease, collagenase, amylase, xylanase, lipase, and phosphatase activities. Keratinases of the strain showed maximum activity at 70°C and pH 9.0 as well as high thermal stability. A mass-spectrometric analysis identified seven peptidases with molecular masses of 26.8-154.8 kDa in the secretory proteome. These peptidases are members of S8 and S41 serine peptidase families and of M14, M42, and M55 metallopeptidase families. Additionally, α-amylase (55.2 kDa), alkaline phosphatase (59.8 kDa), and esterase (26.8 kDa) were detected. The strong keratinolytic properties of the strain were confirmed by degradation of chicken and goose feathers, which got completely hydrolyzed within 4 days. Submerged fermentation by strain B. paralicheniformis T7 was carried out in a pilot bioreactor, where the highest keratinase production was noted after 19 h of cultivation. After the fermentation, in the culture fluid, the keratinase activity toward keratin azure was 63.6 ± 5.8 U/mL. The protease activity against azocasein was 715.7 ± 40.2 U/mL. The possibility of obtaining enzyme preparations in liquid and powder form was demonstrated, and their comparative characteristics are given. In the concentrate, the keratinase, protease, α-amylase, phosphatase, and esterase/lipase activities were 2,656.7 ± 170.4, 29,886.7 ± 642.9, 176.1 ± 16.3, 23.9 ± 1.8, and 510.9 ± 12.2 U/mL, respectively. In the lyophilizate, these activities were 57,733.3 ± 8,911.4, 567,066.7 ± 4,822.2, 2,823.0 ± 266.8, 364.2 ± 74.8, and 17,618.0 ± 610.3 U/g, respectively. In the preparation obtained by air flow drying at 55°C, these activities were 53,466.7 ± 757.2, 585,333.3 ± 4,277.1, 2,395.8 ± 893.7, 416.7 ± 52.4, and 15,328.1 ± 528.6 U/g, respectively. The results show high potential of B. paralicheniformis strain T7 as a producer of keratinases and other enzymes for applications in agricultural raw materials and technologies for processing of keratin-containing animal waste.

Harnessing the potential of microbial keratinases for bioconversion of keratin waste

The increasing global consumption of poultry meat has led to the generation of a vast quantity of feather keratin waste daily, posing significant environmental challenges due to improper disposal methods. A growing focus is on utilizing keratinous polymeric waste, amounting to millions of tons annually. Keratins are biochemically rigid, fibrous, recalcitrant, physiologically insoluble, and resistant to most common proteolytic enzymes. Microbial biodegradation of feather keratin provides a viable solution for augmenting feather waste's nutritional value while mitigating environmental contamination. This approach offers an alternative to traditional physical and chemical treatments. This review focuses on the recent findings and work trends in the field of keratin degradation by microorganisms (bacteria, actinomycetes, and fungi) via keratinolytic and proteolytic enzymes, as well as the limitations and challenges encountered due to the low thermal stability of keratinase, and degradation in the complex environmental conditions. Therefore, recent biotechnological interventions such as designing novel keratinase with high keratinolytic activity, thermostability, and binding affinity have been elaborated here. Enhancing protein structural rigidity through critical engineering approaches, such as rational design, has shown promise in improving the thermal stability of proteins. Concurrently, metagenomic annotation offers insights into the genetic foundations of keratin breakdown, primarily predicting metabolic potential and identifying probable keratinases. This may extend the understanding of microbial keratinolytic mechanisms in a complex community, recognizing the significance of synergistic interactions, which could be further utilized in optimizing industrial keratin degradation processes.

Design, development and characterization of a chimeric protein with disulfide reductase and protease domain showing keratinase activity

Keratin is one of the major components of solid waste, and the degradation products have extensive applications in various commercial industries. Due to the complexity of the structure of keratin, especially the disulfide bonds between keratin polypeptides, keratinolytic activity is efficient with a mixture of proteins with proteases, peptidases, and oxidoreductase activity. The present work aimed to create an engineered chimeric protein with a disulfide reductase domain and a protease domain connected with a flexible linker. The structure, stability, and substrate interaction were analyzed using the protein modeling tools and codon-optimized synthetic gene cloned, expressed, and purified using Ni2+-NTA chromatography. The keratinolytic activity of the protein was at its maximum at 70 °C. The suitable pH for the enzyme activity was pH 8. While Ni2+, Mg2+, and Na+ inhibited the keratinolytic activity, Cu2+, Ca2+, and Mn2+ enhanced it significantly. Biochemical characterization of the protease domain indicated significant keratinolytic activity at 70 °C at pH 10.0 but was less efficient than the chimeric protein. Experiments using feathers as the substrate showed a clear degradation pattern in the SEM analysis. The samples collected from the degradation experiments indicated the release of proteins (2-fold) and amino acids (8.4-fold) in a time-dependent manner. Thus, the protease with an added disulfide reductase domain showed excellent keratin degradation activity and has the potential to be utilized in the commercial industries.

Study on the adsorption process and kinetic, thermodynamic of bio-based waste cattle hair powder toward acidic complex dye

In this paper, cattle hair waste (CHW) was collected and physically milled into different meshes of ultrafine cattle hair powder (UCHP). The reuse of CHW reaches the purpose of treating pollution with waste by using bio-base adsorbent. It was characterized by using scanning electron microscope-energy dispersive spectrometer (SEM-EDS), Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), differential scanning calorimeter (DSC), and X-ray diffraction (XRD). The adsorption studies were carried out under different conditions of temperature, time, pH, concentration of dye solution, mesh size, and dosage of cattle hair powder, respectively. The pseudo-first and pseudo-secondary kinetics and intra-particle diffusion models were employed to analyze the adsorption kinetic. The Langmuir, Freundlich, and Temkin adsorption isotherm was used to analyze the adsorption isotherm. The results showed that the adsorption capacity of UCHP for acidic metal complex (Trupoxane Brown R6) dyes increased with the decreasing pH solution. The adsorption capacity of 200 mesh UCHP was 379.5 mg.g-1 when the adsorption conditions were as follows: 100 mL dye solution with the initial concentration of 1000 mg·L-1, the dosage of adsorbent was 0.1 g, the pH was 3 for 12 h at 40 °C. The kinetic model fitting results showed that the adsorption of dyes by UCHP conformed to the pseudo-second-order kinetic model. Adsorption thermodynamics study showed that the Langmuir model has the highest fitting result. The amino group contained on the surface of cattle hair powder and the amide bond contained in the molecular chain of peptide chain have better electrostatic adsorption binding force for acid metal complex dyes, and the binding between them is mainly electrostatic attraction. The experimental results show that the ultrafine powder has better adsorption property, which provides a high-value conversion way for recycling waste cattle hair.

Recovery of pure PET from wool/PET/elastane textile waste through step-wise enzymatic and chemical processing

Textile waste is mostly incinerated because few recycling processes are available to recover valuable materials. In this work, a feasible chemo-enzymatic recycling process of wool/polyethylene terephthalate (PET)/elastane blends to recover pure PET is for the first time successfully demonstrated. Two novel enzyme formulations were selected for wool hydrolysis, whereas the recovered amino acids were quantified using high-performance liquid chromatography and two assays (Ninhydrin and Folin-Ciocalteu). Kinetic studies on the amino acid formation alongside reaction observations by scanning electron microscopy proved sufficient removal of wool within 8 hours with the new enzyme formulation, marking an acceleration compared to previous studies. Finally, elastane was separated with a non-hazardous solvent to obtain pure PET. Tensile tests on the recovered PET fibres reveal only slight changes through the enzymatic treatment and no changes induced by the applied solvent. The enzyme formulation was successfully tested on five different post-consumer wool/PET textile waste samples. This valorization approach enhances the circular economy concept for textile waste recycling.

Construction of artificial microbial consortia for efficient degradation of chicken feathers and optimization of degradation conditions

Microbes within a consortium exhibit a synergistic interaction, enhancing their collective capacity to perform functions more effectively than a single species, especially in the degradation of keratin-rich substrates. To achieve a more stable and efficient breakdown of chicken feathers, a comprehensive screening of over 9,000 microbial strains was undertaken. This meticulous selection process identified strains with the capability to degrade keratin effectively. Subsequently, antagonistic tests were conducted to isolate strains of fungi and bacteria that were non-antagonistic, which were then used to form the artificial microbial consortia. The optimal fermentation conditions for the keratinophilic microbial consortia were determined through the optimization of response surface methodology. The results revealed that 11 microbial strains-comprising of 4 fungi and 7 bacteria-were particularly proficient in degrading chicken feathers. The artificially constructed microbial consortia (AMC) comprised two bacterial strains and one fungal strain. The optimal conditions for feathers degradation were identified as a 10 g/L concentration of chicken feathers, a 2.6% microbial inoculation volume and a fermentation fluid pH of 9. Under these conditions, the degradation rate for chicken feathers reached a significant 74.02%, representing an 11.45% increase over the pre-optimization rate. The AMC developed in this study demonstrates the potential for efficient and economical process of livestock and poultry feathers. It provides innovative insights and a theoretical foundation for tackling the challenging degradation of keratin-rich materials. Furthermore, this research lays the groundwork for the separation and purification of keratins, as well as the development of novel proteases, which could have profound implications for a range of applications.

Synthesis of Keratin Nanoparticles Extracted from Human Hair through Hydrolysis with Concentrated Sulfuric Acid: Characterization and Cytotoxicity

Human hair, composed primarily of keratin, represents a sustainable waste material suitable for various applications. Synthesizing keratin nanoparticles (KNPs) from human hair for biomedical uses is particularly attractive due to their biocompatibility. In this study, keratin was extracted from human hair using concentrated sulfuric acid as the hydrolysis agent for the first time. This process yielded KNPs in both the supernatant (KNPs-S) and precipitate (KNPs-P) phases. Characterization involved scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), Zeta potential analysis, X-ray diffraction (XRD), and thermogravimetric analysis (TG). KNPs-S and KNPs-P exhibited average diameters of 72 ± 5 nm and 27 ± 5 nm, respectively. The hydrolysis process induced a structural rearrangement favoring β-sheet structures over α-helices in the KNPs. These nanoparticles demonstrated negative Zeta potentials across the pH spectrum. KNPs-S showed higher cytotoxicity (CC50 = 176.67 µg/mL) and hemolytic activity, likely due to their smaller size compared to KNPs-P (CC50 = 246.21 µg/mL), particularly at concentrations of 500 and 1000 µg/mL. In contrast, KNPs-P did not exhibit hemolytic activity within the tested concentration range of 32.5 to 1000 µg/mL. Both KNPs demonstrated cytocompatibility with fibroblast cells in a dose-dependent manner. Compared to other methods reported in the literature and despite requiring careful washing and neutralization steps, sulfuric acid hydrolysis proved effective, rapid, and feasible for producing cytocompatible KNPs (biomaterials) in single-step synthesis.

First Insight into the Degradome of Aspergillus ochraceus: Novel Secreted Peptidases and Their Inhibitors

Aspergillus fungi constitute a pivotal element within ecosystems, serving as both contributors of biologically active compounds and harboring the potential to cause various diseases across living organisms. The organism's proteolytic enzyme complex, termed the degradome, acts as an intermediary in its dynamic interaction with the surrounding environment. Using techniques such as genome and transcriptome sequencing, alongside protein prediction methodologies, we identified putative extracellular peptidases within Aspergillus ochraceus VKM-F4104D. Following manual annotation procedures, a total of 11 aspartic, 2 cysteine, 2 glutamic, 21 serine, 1 threonine, and 21 metallopeptidases were attributed to the extracellular degradome of A. ochraceus VKM-F4104D. Among them are enzymes with promising applications in biotechnology, potential targets and agents for antifungal therapy, and microbial antagonism factors. Thus, additional functionalities of the extracellular degradome, extending beyond mere protein substrate digestion for nutritional purposes, were demonstrated.

Transcriptomics Reveals the Mechanism of Purpureocillium lilacinum GZAC18-2JMP in Degrading Keratin Material

Microbial degradation of keratin is characterized by its inherent safety, remarkable efficiency, and the production of copious degradation products. All these attributes contribute to the effective management of waste materials at high value-added and in a sustainable manner. Microbial degradation of keratin materials remains unclear, however, with variations observed in the degradation genes and pathways among different microorganisms. In this study, we sequenced the transcriptome of Purpureocillium lilacinum GZAC18-2JMP mycelia on control medium and the medium containing 1% feather powder, analyzed the differentially expressed genes, and revealed the degradation mechanism of chicken feathers by P. lilacinum GZAC18-2JMP. The results showed that the chicken feather degradation rate of P. lilacinum GZAC18-2JMP reached 64% after 216 h of incubation in the fermentation medium, reaching a peak value of 148.9 μg·mL-1 at 192 h, and the keratinase enzyme activity reached a peak value of 211 U·mL-1 at 168 h, which revealed that P. lilacinum GZAC18-2JMP had a better keratin degradation effect. A total of 1001 differentially expressed genes (DEGs) were identified from the transcriptome database, including 475 upregulated genes and 577 downregulated genes. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis of the DEGs revealed that the metabolic pathways related to keratin degradation were mainly sulfur metabolism, ABC transporters, and amino acid metabolism. Therefore, the results of this study provide an opportunity to gain further insight into keratin degradation and promote the biotransformation of feather wastes.

Bacillus velezensis strain NA16 shows high poultry feather-degrading efficiency, protease and amino acid production

Isolated Bacillus velezensis strain NA16, which produces proteases, amino acids and the transcription levels of different keratinolytic enzymes and disulfide reductase genes in whole gene sequencing, was evaluated during feather degradation. The result shows under optimum fermentation conditions, chicken feather fermentation showed total amino acid concentration of 7599 mg/L, degradation efficiency of 99.3% at 72 h, and protease activity of 1058 U/mL and keratinase activity of 288 U/mL at 48 h. Goose feather fermentation showed total amino acid concentration of 4918 mg/L (96 h), and degradation efficiency was 98.9% at 120 h. Chicken feather fermentation broth at 72 h showed high levels of 17 amino acids, particularly phenylalanine (1050 ± 1.90 mg/L), valine (960 ± 1.04 mg/L), and glutamic (950 ± 3.00 mg/L). Scanning electron microscopy and Fourier transform infrared analysis revealed the essential role of peptide bond cleavage in structural changes and degradation of feathers. Protein purification and zymographic analyses revealed a key role in feather degradation of the 39-kDa protein encoded by gene1031, identified as an S8 family serine peptidase. Whole genome sequencing of NA16 revealed 26 metalloproteinase genes and 22 serine protease genes. Among the proteins, S8 family serine peptidase (gene1031, gene1428) and S9 family peptidase (gene3132) were shown by transcription analysis to play major roles in chicken feather degradation. These findings revealed the transcription levels of different families of keratinolytic enzymes in the degradation of feather keratin by microorganisms, and suggested potential applications of NA16 in feather waste management and amino acid production.

Unveiling the potential of biomaterials and their synergistic fusion in tissue engineering

Inspired by nature, tissue engineering aims to employ intricate mechanisms for advanced clinical interventions, unlocking inherent biological potential and propelling medical breakthroughs. Therefore, medical, and pharmaceutical fields are growing interest in tissue and organ replacement, repair, and regeneration by this technology. Three primary mechanisms are currently used in tissue engineering: transplantation of cells (I), injection of growth factors (II) and cellular seeding in scaffolds (III). However, to develop scaffolds presenting highest potential, reinforcement with polymeric materials is growing interest. For instance, natural and synthetic polymers can be used. Regardless, chitosan and keratin are two biopolymers presenting great biocompatibility, biodegradability and non-antigenic properties for tissue engineering purposes offering restoration and revitalization. Therefore, combination of chitosan and keratin has been studied and results exhibit highly porous scaffolds providing optimal environment for tissue cultivation. This review aims to give an historical as well as current overview of tissue engineering, presenting mechanisms used and polymers involved in the field.

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.

Food waste-based bio-fertilizers production by bio-based fermenters and their potential impact on the environment

Increasing food waste is creating a global waste (and management) crisis. Globally, ∼1.6 billion tons of food is wasted annually, worth ∼$1.2 trillion. By reducing this waste or by turning it into valuable products, numerous economic advantages can be realized, including improved food security, lower production costs, biodegradable products, environmental sustainability, and cleaner solutions to the growing world's waste and garbage management. The appropriate handling of these detrimental materials can significantly reduce the risks to human health. Food waste is available in biodegradable forms and, with the potential to speed up microbial metabolism effectively, has immense potential in improving bio-based fertilizer generation. Synthetic inorganic fertilizers severely affect human health, the environment, and soil fertility, thus requiring immediate consideration. To address these problems, agricultural farming is moving towards manufacturing bio-based fertilizers via utilizing natural bioresources. Food waste-based bio-fertilizers could help increase yields, nutrients, and organic matter and mitigate synthetic fertilizers' adverse effects. These are presented and discussed in the review.

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.

Rhizoctonia solani disease suppression: addition of keratin-rich soil amendment leads to functional shifts in soil microbial communities

Promoting soil suppressiveness against soil borne pathogens could be a promising strategy to manage crop diseases. One way to increase the suppression potential in agricultural soils is via the addition of organic amendments. This microbe-mediated phenomenon, although not fully understood, prompted our study to explore the microbial taxa and functional properties associated with Rhizoctonia solani disease suppression in sugar beet seedlings after amending soil with a keratin-rich waste stream. Soil samples were analyzed using shotgun metagenomics sequencing. Results showed that both amended soils were enriched in bacterial families found in disease suppressive soils before, indicating that the amendment of keratin-rich material can support the transformation into a suppressive soil. On a functional level, genes encoding keratinolytic enzymes were found to be abundant in the keratin-amended samples. Proteins enriched in amended soils were those potentially involved in the production of secondary metabolites/antibiotics, motility, keratin-degradation, and contractile secretion system proteins. We hypothesize these taxa contribute to the amendment-induced suppression effect due to their genomic potential to produce antibiotics, secrete effectors via the contractile secretion system, and degrade oxalate-a potential virulence factor of R. solani-while simultaneously possessing the ability to metabolize keratin.

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.

Isolation, identification, and molecular characterization of potential keratinolytic fungus sp. from Southern Assam: relevance to poultry wastes and its biological management

Feather waste is a highly prevalent form of keratinous waste that is generated by the poultry industry. The global daily production of feather waste has been shown to approach 5 million tons, typically being disposed of through methods such as dumping, landfilling, or incineration which contribute significantly to environmental pollutions. The proper management of these keratinous wastes is crucial to avoid environmental contamination. The study was carried out to isolate the keratinolytic fungi from the poultry disposal sites of different region of North-East India to evaluate its potential in bioremediation of the feathers wastes. Out of 12 fungal strains isolated from the sites, the fungus showing the highest zone of hydrolysis on both the skim milk and keratin agar medium was selected for the study and the molecular identification of the isolate was performed through DNA sequence analysis by amplifying the internal transcribed spacer (ITS) region. The sequence results showed higher similarity (above 95%) with Aspergillus spp. and was named Aspergillus sp. Iro-1. The strain was further analyzed for its feather degrading potential which was performed in submerged conditions under optimized conditions. The study showed that the strain could effectively degrade the feathers validated through weight loss method, and the structural deformations in the feathers were visualized through scanning electron microscopy (SEM). Aspergillus sp. Iro-1 was obtained from the southern region of Assam. It would be of great importance as the implementation of this sp. can help in the bioremediation of feathers wastes in this region. This is the first study of identification of feather degrading fungus from southern part of Assam (Barak).

A clinical prevalence of dermatophytic mycoses with an assessment of its clinical manifestations in a tertiary care hospital at Salem, South India

BACKGROUND

Dermatophytosis is very common among all age groups throughout the world. The incidence of the same is increasing on a steady basis.

AIM

Estimating the clinical prevalence of dermatophytes mycoses among the patients visiting the outpatient unit and assessing its distinct manifestations.

METHODOLOGY

A prospective observational study was conducted with the patients attending the Skin and STD outpatient unit of a tertiary care teaching hospital in Salem. A total of 3068 outpatients attended the department, of which 420 patients were diagnosed with dermatophytic mycoses and were taken for investigating the prevalence.

RESULTS

A total of 420 dermatophytosis patients were included giving a percentage prevalence of 13.69%. There were more female patients (n = 213, 50.71%) than males (n = 207, 49.29%). The most common afflicted age group was 31-40 years (n = 99, 50.71%). Most of the patients had an atypical lesion called tinea incognita (n = 265, 63.09%) where there was no typical classic appearance of dermatophytic infections. The most prevalent clinical manifestation was tinea corporis (n = 73, 17.38%) followed by tinea cruris (n = 69, 16.43%). There were more newly diagnosed dermatophytosis cases (n = 326) than the previously diagnosed cases (n = 94).

CONCLUSION

This study concludes that dermatophytic mycoses were more prevalent among females than males and among the age groups of 31-40 years. The most common clinical presentation was tinea incognita followed by tinea corporis.

Feather meal processing methods impact the production parameters, blood biochemical indices, gut function, and hepatic enzyme activity in broilers

This study investigated the effects of feather meal (FM) processing methods on production parameters, blood biochemical indices, intestinal morphology, digestive and hepatic enzyme activities, and gastrointestinal tract pH and microflora of broilers. A total of 480-d-old male broilers were used for 42 d in a completely randomized design with eight treatments and five replicates (12 chicks/replicate). Treatments were 1) a control diet (without FM), 2) a diet containing 4% raw FM (RFM), 3) a diet containing 4% processed FM (PFM) by autoclave (Au-PFM), 4) a diet containing 4% fermented FM (FFM) by Bacillus licheniformis (Bl-FFM), 5) a diet containing 4% FFM by Bacillus subtilis (Bs-FFM), 6) a diet containing 4% FFM by Aspergillus niger (An-FFM), 7) a diet containing 4% FFM by B. licheniformis + B. subtilis + A. niger (Co-FFM), and 8) a diet containing 4% PFM by an enzyme (En-PFM). Results showed that in the FFMs the contents of ash, ether extract, total volatile nitrogen, and amino acids including Lys, Met, Thr, Trp, His, Leu, Gly, Ile, Phe, and Tyr increased (P < 0.05), while crude fiber, crude protein, and dry matter content decreased (P < 0.05). Compared with the control, the Co-FFM diet had no significant differences (P > 0.05) in total body weight gain (2,827 vs. 2,791 g/chick), total feed intake (5,018 vs. 4,991 g/chick), European production efficiency factor (375 vs. 377), European Broiler Index (371 vs. 371), and feed conversion ratio (1.77 vs. 1.78 g/g). Feeding FFM decreased (P < 0.05) serum total cholesterol (1.46-fold), triglyceride (1.61-fold), very low-density lipoprotein cholesterol (1.61-fold), and low-density lipoprotein cholesterol (2.27-fold) compared to the control. Also, FFM increased (P < 0.05) villus height (1,045 to 1,351, 661 to 854, and 523 to 620 μm), and villus height to crypt depth ratio (6.15 to 8.45, 4.55 to 7.04, and 4.27 to 5.45), in the duodenum, jejunum, and ileum, respectively, compared to the control. Compared to the control, the Co-FFM diet increased (P < 0.05) protease (34, 39, and 45 %) in the pancreas, duodenum, and jejunum, as well as amylase (73, and 97 %) activities in the duodenum, and jejunum, respectively. Diets containing FFM reduced (P < 0.05) pH in the crop, gizzard, and ileum, and decreased (P < 0.05) Escherichia coli (6.12 to 5.70) count in ileum compared to the control. The Co-FFM diet increased (P < 0.05) lactic acid bacteria count in crop (6.77 to 7.50) and ileum (6.94 to 7.73), also decreased (P < 0.05) coliforms (6.31 to 5.75) count in ileum compared to the control. In conclusion, FM fermentation, particularly Co-FFM, improves the nutritional value of FM, converting it into a decent source of dietary protein for broilers.

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.

Non-deteriorative eco-friendly water-saving tactic for removal of vegetable matters from wool fleece using xylanase and cellulase

The carbonization of wool fleece (WF) is conducted to remove the adhered vegetable matter (VM) from contaminated WF using sulfuric acid, followed by drying and backing. This process has a deteriorative effect on WF and requires a tremendous quantity of water for rinsing WF after carbonization to remove any H2SO4 residuals. Herein, we propose an alternative eco-friendly water-saving process for the removal of VM from WF using enzymes. Cellulase-containing xylanase from the fungus Aspergillus terreus, and cellulase-free xylanase from the fungus Aspergillus flavus AW1 were used to remove the VM from WF. The effect of some process parameters on the amount of the removed VM was assessed. Alkali solubility as well as sulfur and cystine content were used to follow the alteration in the chemistry of the bio-treated WF. The fiber morphology was examined using scanning electron microscopy. The dyeability of the treated WF towards acid, reactive, and basic dyes was monitored. The results revealed that the removal of the VM from WF by applying the examined enzymes was effective and could be an appropriate, non-destructive, eco-friendly water-saving substitute to the conventional carbonization procedures. By virtue of enzyme specificity, the proposed process removed the VM without deteriorating the fiber.

Novel Antioxidant Peptides Derived from Feather Keratin Alleviate H2O2-Induced Oxidative Damage in HepG2 Cells via Keap1/Nrf2 Pathway

Reactive oxygen species (ROS) are crucial for signal transduction and the maintenance of cellular homeostasis. However, superfluous ROS may engender chronic pathologies. Feather keratin is a promising new source of antioxidant peptides that can eliminate excess ROS and potentially treat oxidative stress-related diseases, but the underlying mechanisms have remained elusive. This study investigated the antioxidant effects and mechanisms against H2O2-induced oxidative damage in HepG2 cells of the two latest discovered antioxidant peptides, CRPCGPTP (CP-8) and ANSCNEPCVR (AR-10), first decrypted from feather keratin. The results revealed that CP-8 and AR-10 did not exhibit cytotoxicity to HepG2 cells while reducing intracellular ROS accumulation. Simultaneously, they enhanced the activities of catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px), thus alleviating H2O2-induced cell apoptosis. Molecular docking analysis demonstrated that CP-8, AR-10 interacted well with the key amino acids in the Kelch domain of Keap1, thereby directly disrupting the Keap1-Nrf2 interaction. The peptides' biosafety and antioxidant activity via Keap1/Nrf2 signaling lay the groundwork for further animal studies and applications as functional food additives.

The flexible linker and CotG were more effective for the spore surface display of keratinase KERQ7

Feather, horn, hoof, and other keratin waste are protein-rich but limited by natural keratinase synthesis, activity, pH, and temperature stability. It is challenging to realize its large-scale application in industries. Bacillus subtilis spores are a safe, efficient, and highly resistant immobilized carrier, which can improve target proteins' resistance. In this research, KERQ7, the keratinase gene of Bacillus tequilensis strain Q7, was fused to the Bacillus subtilis genes coding for the coat proteins CotG and CotB, respectively, and displayed on the surface of B. subtilis spores. Compared with the free KERQ7, the immobilized KERQ7 showed a greater pH tolerance and heat resistance on the spore surface. The activity of CotG-KERQ7 is 1.25 times that of CotB-KERQ7, and CotG-KERQ7 is more stable. When the flexible linker peptide L3 was used to connect CotG and KERQ7, the activity was increased to 131.2 ± 3.4%, and the residual enzyme activity was still 62.5 ± 2.2% after being kept at 60 ℃ for 4 h. These findings indicate that the flexible linker and CotG were more effective for the spore surface display of keratinase to improve stress resistance and promote its wide application in feed, tanning, washing, and other industries.

Comet assay as a suitable biomarker for in vivo oral carcinogenesis: a systematic review

BACKGROUND AND OBJECTIVES

In order to detect genetic damage, different methods have been developed, such as micronuclei and comet assay. The comet assay presents some advantages when compared to the other aforementioned methods, including wide versatility, as any eukaryotic cell can be evaluated at an individual cellular level. In this context, the aim of this systematic review was designed to help further elucidate the following question: is the comet assay a suitable biomarker of in vivo oral carcinogenesis?

MATERIAL AND METHODS

The present systematic review was performed in accordance with the Preferred Reporting Items for Systematic Review and Meta-Analyses (PRISMA) guidelines. Full manuscripts from 18 studies were carefully selected in this setting.

RESULTS

A total of 15 studies demonstrated positive findings for genotoxicity in peripheral blood or oral cells in patients with pre-malignant lesions or oral cancer. In the quality assessment of studies, 1 was classified as Strong, 5 were considered as Moderate, and 12 were classified as Weak.

CONCLUSION

In summary, the comet assay can be a useful biomarker for oral carcinogenesis. However, further studies with more strict parameters are suggested (with less uncontrolled confounders) in order to increase findings reliability for diagnosis of oral potentially malignant lesions.

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.

Multi-omics study of sulfur metabolism affecting functional microbial community succession during aerobic solid-state fermentation

Microbial-mediated sulfur metabolism is closely related to carbon and nitrogen metabolism in natural biological systems. In this study, the effects of sulfur metabolism on microbial communities and functional enzyme succession were investigated based on integrated multi-omics by adding sulfur-containing compounds to aerobic fermentation systems. Sulfur powder was oxidized to S2O32- and subsequently to SO42- by the microbial sulfur-oxidizing system, which lowered the pH to 7.5 on day 7. The decrease in pH resulted in Planifilum (secreted S8, M17 and M32 proteases) losing its competitive advantage, whereas Novibacillus (secreted M14 and M19 metalloproteases) became dominant. Structural proteomics indicated that the surface of Novibacillus proteases has more negatively charged amino acid residues that help maintain protein stability at low pH. These findings aid understanding of the effects of sulfur metabolism on fermentation and the mechanism of microbial adaptation after pH reduction, providing new perspectives on the optimization of fermentation processes.

Unleashing the Potential of Bacterial Isolates from Apple Tree Rhizosphere for Biocontrol of Monilinia laxa: A Promising Approach for Combatting Brown Rot Disease

Monilinia laxa, a notorious fungal pathogen responsible for the devastating brown rot disease afflicting apples, wreaks havoc in both orchards and storage facilities, precipitating substantial economic losses. Currently, chemical methods represent the primary means of controlling this pathogen in warehouses. However, this study sought to explore an alternative approach by harnessing the biocontrol potential of bacterial isolates against brown rot in apple trees. A total of 72 bacterial isolates were successfully obtained from the apple tree rhizosphere and subjected to initial screening via co-cultivation with the pathogen. Notably, eight bacterial isolates demonstrated remarkable efficacy, reducing the mycelial growth of the pathogen from 68.75 to 9.25%. These isolates were subsequently characterized based on phenotypic traits, biochemical properties, and 16S rRNA gene amplification. Furthermore, we investigated these isolates' production capacity with respect to two enzymes, namely, protease and chitinase, and evaluated their efficacy in disease control. Through phenotypic, biochemical, and 16S rRNA gene-sequencing analyses, the bacterial isolates were identified as Serratia marcescens, Bacillus cereus, Bacillus sp., Staphylococcus succinus, and Pseudomonas baetica. In dual culture assays incorporating M. laxa, S. marcescens and S. succinus exhibited the most potent degree of mycelial growth inhibition, achieving 68.75 and 9.25% reductions, respectively. All the bacterial isolates displayed significant chitinase and protease activities. Quantitative assessment of chitinase activity revealed the highest levels in strains AP5 and AP13, with values of 1.47 and 1.36 U/mL, respectively. Similarly, AP13 and AP6 exhibited the highest protease activity, with maximal enzyme production levels reaching 1.3 and 1.2 U/mL, respectively. In apple disease control assays, S. marcescens and S. succinus strains exhibited disease severity values of 12.34% and 61.66% (DS), respectively, highlighting their contrasting efficacy in mitigating disease infecting apple fruits. These findings underscore the immense potential of the selected bacterial strains with regard to serving as biocontrol agents for combatting brown rot disease in apple trees, thus paving the way for sustainable and eco-friendly alternatives to chemical interventions.