Purification and partial characterization of serine-metallokeratinase from a newly isolated Bacillus pumilus NRC21

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.

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.

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.

Efficient valorization of feather waste by Bacillus cereus IIPK35 for concomitant production of antioxidant keratin hydrolysate and milk-clotting metallo-serine keratinase

Keratinase production by Bacillus cereus IIPK35 was investigated under solid-state fermentation (SSF) and the maximum titer of 648.28 U/gds was revealed. Feather hydrolysates obtained from SSF exhibited paramount antioxidant properties in ABTS [2,2'-azinobis-(3-ethylbenzothiazoline)-6-sulfonic acid], FRAP [Ferric ion reducing antioxidant power], and DPPH [2,2,-Diphenyl-1-picrylhydrazyl] assay. The keratinase was purified up to homogeneity have a molecular weight of 42 kDa, and showed its stability between pH 6.5-10.0 and temperature 35-60 °C with optimum enzyme activity at pH 9.0 and 55 °C. The catalytic indices viz. Km of 9.8 mg/ml and Vmax of 307.7 μmol/min for keratin were determined. Besides keratin, the enzyme displayed broad and proteolytic activity towards other proteinaceous substrates such as casein, skim milk, gelatin, and bovine serum albumin. Pure keratinase activity was stimulated in presence of Ca²⁺ and Mg²⁺ ions, while it was strongly inhibited by both iodoacetamide and EDTA, indicating it to be a metallo-serine protease in nature. Circular dichroism study endorses the structural stability of the secondary structure at the said range of pH and temperature. The IIPK35 keratinase is non-cytotoxic in nature, shows remarkable storage stability and is stable in presence of Tween 80, Triton X 100, and sodium sulfite. Furthermore, it showed excellent milk clotting potential (107.6 Soxhlet Unit), suggesting its usefulness as an alternative milk clotting agent in the dairy industry. This study unlocks a new gateway for keratinase investigation in SSF using chicken feathers as substrate and biochemical and biophysical characterization of keratinase for better understanding and implication in industrial applications.

Replacement of Trypsin by Proteases for Medical Applications

BACKGROUND

Cell culture has a crucial role in many applications in biotechnology. The production of vaccines, recombinant proteins, tissue engineering, and stem cell therapy all need cell culture. Most of these activities needed adherent cells to move, which should be trypsinized several times until received on a large scale. Although trypsin is manufactured from the bovine or porcine pancreas, the problem of contamination by unwanted animal proteins, unwanted immune reactions, or contamination to pathogen reagents is the main problem.

OBJECTIVES

This study investigated microbial proteases as a safe alternative for trypsin replacement in cell culture experiments for the detachment of adherent cells.

METHODS

The bacteria were isolated from the leather industry effluent based on their protease enzymes. After sequencing their 16S ribosomal deoxyribonucleic acid, their protease enzymes were purified, and their enzyme activities were assayed. The alteration of enzymatic activities using different substrates and the effect of substrate concentrations on enzyme activities were determined. The purified proteases were evaluated for cell detachment in the L929 fibroblast cells compared to trypsin. The separated cells were cultured again, and cell proliferation was determined by the MTT assay.

RESULTS

The results showed that the isolated bacteria were Bacillus pumilus, Stenotrophomonas sp., Klebsiella aerogenes, Stenotrophomonas maltophilia, and Bacillus licheniformis. Among the isolated bacteria, the highest and the lowest protease activity belonged to Stenotrophomonas sp. and K. aerogenes, with 60.34 and 11.09 U/mL protease activity, respectively. All the isolated microbial proteases successfully affected L929 fibroblast cells' surface proteins and detached the cells. A significant induction in cell proliferation was observed in the cells treated with K. aerogenes protease and B. pumilus protease, respectively (P < 0.05).

CONCLUSIONS

The obtained results suggested that microbial proteases can be used as safe and efficient alternatives to trypsin in cell culture in biopharmaceutical applications.

Production of surfactant-stable keratinase from Bacillus cereus YQ15 and its application as detergent additive

Background

With the growing concern for the environment, there are trends that bio-utilization of keratinous waste by keratinases could ease the heavy burden of keratinous waste from the poultry processing and leather industry. Especially surfactant-stable keratinases are beneficial for the detergent industry. Therefore, the production of keratinase by Bacillus cereus YQ15 was improved; the characterization and use of keratinase in detergent were also studied.

Results

A novel alkaline keratinase-producing bacterium YQ15 was isolated from feather keratin-rich soil and was identified as Bacillus cereus. Based on the improvement of medium components and culture conditions, the maximum keratinase activity (925 U/mL) was obtained after 36 h of cultivation under conditions of 35 °C and 160 rpm. Moreover, it was observed that the optimal reacting temperature and pH of the keratinase are 60 °C and 10.0, respectively; the activity was severely inhibited by PMSF and EDTA. On the contrary, the keratinase showed remarkable stability in the existence of the various surfactants, including SDS, Tween 20, Tween 60, Tween 80, and Triton X-100. Especially, 5% of Tween 20 and Tween 60 increased the activity by 100% and 60%, respectively. Furtherly, the keratinase revealed high efficiency in removing blood stains.

Conclusion

The excellent compatibility with commercial detergents and the high washing efficiency of removing blood stains suggested its suitability for potential application as a bio-detergent additive.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12896-022-00757-3.

Structure, Application, and Biochemistry of Microbial Keratinases

Keratinases belong to a class of proteases that are able to degrade keratins into amino acids. Microbial keratinases play important roles in turning keratin-containing wastes into value-added products by participating in the degradation of keratin. Keratin is found in human and animal hard tissues, and its complicated structures make it resistant to degradation by common proteases. Although breaking disulfide bonds are involved in keratin degradation, keratinase is responsible for the cleavage of peptides, making it attractive in pharmaceutical and feather industries. Keratinase can serve as an important tool to convert keratin-rich wastes such as feathers from poultry industry into diverse products applicable to many fields. Despite of some progress made in isolating keratinase-producing microorganisms, structural studies of keratinases, and biochemical characterization of these enzymes, effort is still required to expand the biotechnological application of keratinase in diverse fields by identifying more keratinases, understanding the mechanism of action and constructing more active enzymes through molecular biology and protein engineering. Herein, this review covers structures, applications, biochemistry of microbial keratinases, and strategies to improve its efficiency in keratin degradation.

Microbial enzymes catalyzing keratin degradation: Classification, structure, function

Keratin is an insoluble and protein-rich epidermal material found in e.g. feather, wool, hair. It is produced in substantial amounts as co-product from poultry processing plants and pig slaughterhouses. Keratin is packed by disulfide bonds and hydrogen bonds. Based on the secondary structure, keratin can be classified into α-keratin and β-keratin. Keratinases (EC 3.4.-.- peptide hydrolases) have major potential to degrade keratin for sustainable recycling of the protein and amino acids. Currently, the known keratinolytic enzymes belong to at least 14 different protease families: S1, S8, S9, S10, S16, M3, M4, M14, M16, M28, M32, M36, M38, M55 (MEROPS database). The various keratinolytic enzymes act via endo-attack (proteases in families S1, S8, S16, M4, M16, M36), exo-attack (proteases in families S9, S10, M14, M28, M38, M55) or by action only on oligopeptides (proteases in families M3, M32), respectively. Other enzymes, particularly disulfide reductases, also play a key role in keratin degradation as they catalyze the breakage of disulfide bonds for better keratinase catalysis. This review aims to contribute an overview of keratin biomass as an enzyme substrate and a systematic analysis of currently sequenced keratinolytic enzymes and their classification and reaction mechanisms. We also summarize and discuss keratinase assays, available keratinase structures and finally examine the available data on uses of keratinases in practical biorefinery protein upcycling applications.

Biochemical characterization of an alkaline surfactant-stable keratinase from a new keratinase producer, Bacillus zhangzhouensis

A new keratinase producer, Bacillus sp. BK111, isolated from a poultry feather was identified as Bacillus zhangzhouensis, which is the first report for its keratinolytic activity. The keratinase production was optimized, followed by the enzyme purification and characterization using biochemical assays. A 2.34-fold increase was observed in the enzyme production under optimized conditions. The enzyme was characterized as a serine protease with 42 kDa molecular weight, stable in a wide range of temperature and pH with maximum keratinolytic activity at 60 °C and pH 9.5. The enzyme had a wide range of different substrates with the best performance on the feather meal substrate. Metal ions of Ca²⁺, K⁺, Na⁺ and Mn²⁺ enhanced the enzyme activity. The enzyme showed a great deal of stability in the presence of ethanol, methanol, acetone, 2-propanol, dimethyl sulfoxide, Tween-80 and Triton X-100. Dithiothreitol (DTT), as a reducing agent, caused a twofold increase in keratinolytic activity. The half-life of the enzyme at optimum temperature was calculated to be 125 min and the ratio of keratinolytic:caseinolytic for the enzyme was 0.8. Our results showed the remarkable features of the enzyme that make it suitable for biotechnological usages.

Comprehensive insights into microbial keratinases and their implication in various biotechnological and industrial sectors: A review

Enormous masses of keratinous wastes are annually accumulated in the environment as byproducts of poultry processing and agricultural wastes. Keratin is a recalcitrant fibrous protein, which represents the major constituent of various keratin-rich wastes, which released into the environment in the form of feathers, hair, wool, bristle, and hooves. Chemical treatment methods of these wastes resulted in developing many hazardous gases and toxins to the public health, in addition to the destruction of several amino acids. Accordingly, microbial keratinases have been drawing much interest as an eco-friendly approach to convert keratinous wastes into valuable products. Numerous keratinolytic microorganisms have been identified, which revealed the competence to hydrolyze keratins into peptides and amino acids. Several types of keratinolytic proteases have been produced that possess diverse biochemical characteristics, conferring them the versatility for implementing in multifarious applications such as detergents, leather and textile industries, animal feeding, and production of bio-fertilizers, in addition to medical and pharmaceutical treatments. This review article emphasizes the significance of keratinases and keratinase based-products via comprehensive insights into the keratin structure, diversity of keratinolytic microorganisms, and mechanisms of keratin hydrolysis. Furthermore, we discuss the biochemical properties of the produced keratinases and their feasible applications in diverse disciplines.

Sustainable production, biochemical and molecular characterization of thermo-and-solvent stable alkaline serine keratinase from novel Bacillus pumilus AR57 for promising poultry solid waste management

The increasing amount of recalcitrant keratinous wastes generated from the poultry industry poses a serious threat to the environment. Keratinase have gained much attention to convert these wastes into valuable products. Ever since primitive feathers first appeared on dinosaurs, microorganisms have evolved to degrade this most recalcitrant keratin. In this study, we identified a promising keratinolytic bacterial strain for bioconversion of poultry solid wastes. A true keratinolytic bacterium was isolated from the slaughterhouse soil and was identified and designated as Bacillus pumilus AR57 by 16S rRNA sequencing. For enhanced keratinase production and rapid keratin degradation, the media components and substrate concentration were optimized through shake flask culture. White chicken feather (1% w/v) was found to be the good substrate concentration for high keratinase production when supplemented with simple medium ingredients. The biochemical characterization reveals astounding results which makes the B. pumilus AR57 keratinase as a novel and unique protease. Optimum activity of the crude enzyme was exhibited at pH 9 and 45 °C. The crude extracellular keratinase was characterized as thermo-and-solvent (DMSO) stable serine keratinase. Bacillus pumilus AR57 showed complete degradation (100%) of white chicken feather (1% w/v) within 18 h when incubated in modified minimal medium supplemented with DMSO (1% v/v) at 150 rpm at 37 °C. Keratinase from modified minimal medium supplemented with DMSO exhibits a half-life of 4 days. Whereas, keratinase from the modified minimal medium fortified with white chicken feather (1% w/v) was stable for 3 h only. Feather meal produced by B. pumilus AR57 was found to be rich in essential amino acids. Hence, we proposed B. pumilus AR57 as a potential candidate for the future application in eco-friendly bioconversion of poultry waste and the keratinase could play a pivotal role in the detergent industry. While feather meal may serve as an alternative to produce animal feed and biofertilizers.

Cloning, Expression, and Characterization of a New Glycosaminoglycan Lyase from Microbacterium sp. H14

Glycosaminoglycan (GAG) lyase is an effective tool for the structural and functional studies of glycosaminoglycans and preparation of functional oligosaccharides. A new GAG lyase from Microbacterium sp. H14 was cloned, expressed, purified, and characterized, with a molecular weight of approximately 85.9 kDa. The deduced lyase HCLaseM belonged to the polysaccharide lyase (PL) family 8. Based on the phylogenetic tree, HCLaseM could not be classified into the existing three subfamilies of this family. HCLaseM showed almost the same enzyme activity towards hyaluronan (HA), chondroitin sulfate A (CS-A), CS-B, CS-C, and CS-D, which was different from reported GAG lyases. HCLaseM exhibited the highest activities to both HA and CS-A at its optimal temperature (35 °C) and pH (pH 7.0). HCLaseM was stable in the range of pH 5.0–8.0 and temperature below 30 °C. The enzyme activity was independent of divalent metal ions and was not obviously affected by most metal ions. HCLaseM is an endo-type enzyme yielding unsaturated disaccharides as the end products. The facilitated diffusion effect of HCLaseM is dose-dependent in animal experiments. These properties make it a candidate for further basic research and application.

Trends in extracellular serine proteases of bacteria as detergent bioadditive: alternate and environmental friendly tool for detergent industry

Proteases, one of the largest groups of industrial enzymes occupy a major share in detergent industry. To meet the existing demands, proteases with efficient catalytic properties are being explored from bacteria residing in extreme habitats. Alkaline proteases are also considered as promising candidates for industrial sectors due to the activity and stability under alkaline and harsh environment. Therefore, a systematic review on experimental studies of bacterial proteases was conducted with emphasis on purification, characterization, cloning and expression and their suitability as detergent additive. Relevant searches using a combination of filters/keywords were performed in the online databases; PubMed, Science Direct, Scopus and Web of Science. Over thousands of research papers, 71 articles in Scopus, 48 articles in Science Direct, 18 articles in PubMed and 8 articles in Web of Science were selected with regard to bacterial extracellular proteases till date. Selected articles revealed majority of the studies conducted between the years 2015 and 17 and were focused on purification of proteases from bacteria. Among microbes, a total of 41 bacterial genera have been explored with limited studies from extreme habitats. Majority of the studies have reported the involvement of subtilisin-like serine proteases with effective properties for detergent industries. The studies revealed shifting of trend from purification to cloning to genetic engineering to meet the industrial demands. The present systematic review describes the proteases from extremophilic bacteria and use of biotechnological techniques such as site-directed mutagenesis and codon optimization to engineer enzymes with better hot spots in the active sites to meet industrial challenges.

Characterization and application of keratinolytic paptidases from Bacillus spp

Solid keratin-rich waste management is one of essential research area in nowadays. Conventional chemical and high thermal keratin waste decomposition methods are fully explored and not enough effective for future biotechnology perspectives. However, traditional keratin-rich waste decomposition methods could be replaced by environmentally-friendly and economical microbial keratin waste biodegradation methods without energy wastage and essential amino acids and nutrition elements loss. In this study BPKer and BAKer keratinolytic peptidases from Bacillus sp. AD-W and Bacillus sp. AD-AA3 strains, respectively, were successfully produced, purified and biochemically characterized. Physical and chemical characterization of native BPKer and BAKer suggested that new keratinolytic peptidases are powerful biocatalysts for efficient keratin waste biodegradation and can replace conventional insufficient non-biological hydrolysis processes without energy, important amino acids and nutritional elements loss. High value bio-active hydrolysis products - peptides obtained from keratin waste biodegradation by BPKer and BAKer are suitable for industrial applications in white and green biotechnology.

Effective feather degradation and keratinase production by Bacillus pumilus GRK for its application as bio-detergent additive

An effecient feather-degrading bacterium was isolated from poultry dumping yard and identified as Bacillus pumilus GRK based on 16S rRNA sequencing. Complete feather degradation (98.3±1.52%) with high keratinase production (373±4 U/ml) was observed in 24h under optimized conditions (substrate 1% (w/w); inoculum size 4% (v/v); pH 10; 200rpm at 37°C) with feathers as sole carbon and nitrogen source in tap water. The fermented broth was enriched with amino acids like tryptophan (221.44µg/ml), isoleucine (15.0µg/ml), lysine (10.81µg/ml) and methionine (7.24µg/ml) suggesting its potential use as feed supplement. The keratinase produced was a detergent stable serine protease and its activity was further enhanced by Ca⁺² and Mg⁺². Bacillus pumilus GRK keratinase was successfully utilised as bioadditive in detergent formulations for removing the blood stains from cloth without affecting its fiber and texture.

Biochemical characterization of a novel surfactant-stable serine keratinase with no collagenase activity from Brevibacillus parabrevis CGMCC 10798

Dehairing is a high pollution process in leather industry. Conventionally, the lime-sulfide mediated chemical process for dehairing would lead to the discharge of pollutants and corrosion of industrial equipment. Concerning these problems, keratinase has become a promising candidate for dehairing process in recent years. In this study, a keratinase-producing bacterium was isolated from sheepfold soil and identified as Brevibacillus parabrevis CGMCC 10798 based on the biochemical characteristics and molecular identification. The keratinase was purified to electrophoretic homogeneity with 17.19% of recovery, 13.18 folds of purification and an estimated molecular weight of 28kDa. The enzyme exhibited high keratinase activity and no collagenase activity. Besides, the keratinase showed optimal activity at 60°C and pH 8.0. The enzyme activity could be significantly increased in the presence of Na⁺ and Ca²⁺. And it was inhibited by EDTA, and PMSF, which indicated that the keratinase belongs to serine-metallo protease. The enzyme could remain stable in the presence of surfactants. Especially, 5mM Tween 40 and Triton 100 could improve the activity by 11% and 30%, respectively. Moreover, B. parabrevis keratinase could completely dehair goat wool within 7h, which indicated its application potential in leather industry.

Production of Thermostable Organic Solvent Tolerant Keratinolytic Protease from Thermoactinomyces sp. RM4: IAA Production and Plant Growth Promotion

There are several reports about the optimization of protease production, but only few have optimized the production of organic solvent tolerant keratinolytic proteases that show remarkable exploitation in the development of the non-polluting processes in biotechnological industries. The present study was carried with aim to optimize the production of a thermostable organic solvent tolerant keratinolytic protease Thermoactinomyces sp. RM4 utilizing chicken feathers. Thermoactinomyces sp. RM4 isolated from the soil sample collected from a rice mill wasteyard site near Kashipur, Uttrakhand was identified on the basis of 16S rDNA analysis. The production of organic solvent tolerant keratinolytic protease enzyme by Thermoactinomyces sp. RM4 was optimized by varying physical culture conditions such as pH (10.0), temperature (60°C), inoculum percentage (2%), feather concentration (2%) and agitation rate (2 g) for feather degradation. The result showed that Thermoactinomyces sp. RM4 potentially produces extra-cellular thermostable organic solvent tolerant keratinolytic protease in the culture medium. Further, the feather hydrolysate from keratinase production media showed plant growth promoting activity by producing indole-3-acetic acid itself. The present findings suggest that keratinolytic protease from Thermoactinomyces sp. RM4 offers enormous industrial applications due to its organic solvent tolerant property in peptide synthesis, practical role in feather degradation and potential function in plant growth promoting activity, which might be a superior candidate to keep ecosystem healthy and functional.