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

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.

Natural Products Produced by the Species of Bacillus cereus Group: Recent Updates

Bacillus cereus group produces diverse antimicrobial compounds through different metabolic pathways, including amino acid-based compounds, sugar derivatives, volatile and miscellaneous compounds. These antimicrobial compounds exhibit antibacterial and antifungal activities against various plant pathogens, promoting plant growth and enhancing tolerance to abiotic stresses. They also exhibit nematicidal activities against plant nematodes and antagonistic effects against pathogens in aquatic animals, promoting growth and inducing immune responses. Moreover, B. cereus group bacteria play a significant role in bioremediation by breaking down or neutralizing environmental pollutants, such as plastics, petroleum products, heavy metals, and insecticides. They produce enzymes like laccases, lipases, proteases, and various oxidases, contributing to the degradation of these pollutants. In the food industry, they can cause food poisoning due to their production of enterotoxins. However, they are also utilized in various industrial applications, such as producing environmentally friendly bio-based materials, biofertilizers, and nanoparticles. Notably, B. cereus transforms selenite into selenium nanoparticles, which have health benefits, including cancer prevention. In summary, B. cereus group bacteria have diverse applications in agriculture, bioremediation, industry, and medicine, contributing to sustainable and eco-friendly solutions across multiple fields. In this review, we have revised B. cereus group and the characteristics of every species; we have also highlighted the more important compounds secreted by the species of B. cereus group and the applications of these compounds. The aim is to explain the available secondary metabolites to classify the species from this group, increasing the knowledge about taxonomy of this group.

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.

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.

New Bacillus paralicheniformis strain with high proteolytic and keratinolytic activity

Bacillus paralicheniformis T7, which exhibits high proteolytic and keratinolytic activities, was isolated from soil in Kazakhstan. Its secreted proteases were thermostable and alkaline, demonstrating maximum activity at 70 °C and pH 9.0. The proteases and keratinases of this strain were sensitive to Ni2+, Co2+, Mn2+, and Cd2+, with Cu2+, Co2+ and Cd2+ negatively affecting keratinolytic activity, and Fe3+ ions have a strong inhibitory effect on proteolytic and keratinolytic activity. Seven proteases were identified in the enzymatic extract of B. paralicheniformis T7: four from the serine peptidase family and three from the metallopeptidase family. The proteases hydrolyzed 1 mg of casein, hemoglobin, gelatin, ovalbumin, bovine serum albumin, or keratin within 15 s to 30 min. The high keratinolytic activity of this strain was confirmed through the degradation of chicken feathers, horns, hooves, wool, and cattle hide. Chicken feathers were hydrolyzed in 4 days, and the degrees of hydrolysis for cattle hide, wool, hoof, and horn after 7 days of cultivation were 97.2, 34.5, 29.6, and 3.6%, respectively. During submerged fermentation with feather medium in a laboratory bioreactor, the strain secreted enzymes with 249.20 ± 7.88 U/mL protease activity after 24 h. Thus, B. paralicheniformis T7 can be used to produce proteolytic and keratinolytic enzymes for application in processing proteinaceous raw materials and keratinous animal waste.

Bio-molecular analyses enable new insights into the taphonomy of feathers

Exceptionally preserved feathers from the Mesozoic era have provided valuable insights into the early evolution of feathers and enabled color reconstruction of extinct dinosaurs, including early birds. Mounting chemical evidence for the two key components of feathers-keratins and melanins-in fossil feathers has demonstrated that exceptional preservation can be traced down to the molecular level. However, the chemical changes that keratin and eumelanin undergo during fossilization are still not fully understood, introducing uncertainty in the identification of these two molecules in fossil feathers. To address this issue, we need to examine their taphonomic process. In this study, we analyzed the structural and chemical composition of fossil feathers from the Jehol Biota and compared them with the structural and chemical changes observed in modern feathers during the process of biodegradation and thermal degradation, as well as the structural and chemical characteristics of a Cenozoic fossil feather. Our results suggest that the taphonomic process of feathers from the Cretaceous Jehol Biota is mainly controlled by the process of thermal degradation. The Cretaceous fossil feathers studied exhibited minimal keratin preservation but retained strong melanin signals, attributed to melanin's higher thermal stability. Low-maturity carbonaceous fossils can indeed preserve biosignals, especially signals from molecules with high resistance to thermal degradation. These findings provide clues about the preservation potential of keratin and melanin, and serve as a reference for searching for those two biomolecules in different geological periods and environments.

Isolation, Selection, and Identification of Keratinolytic Bacteria for Green Management of Keratin Waste

The volume of difficult-to-process keratin waste is increasing as a result of rising global meat production. If not properly managed, this waste can contribute to environmental pollution and pose a threat to human and animal welfare. An interesting and more sustainable alternative is therefore the bioconversion of keratin using microorganisms and their enzymes. This work aimed to isolate bacteria from soil samples and zoonotic keratins and to evaluate their enzymatic capacity to degrade α- and β-keratin wastes. A total of 113 bacterial strains were isolated from environmental samples and subjected to taxonomic identification using the MALDI-TOF MS technique and to a two-step screening for proteolytic and keratinolytic activity. The ability to degrade a β-rich keratin substrate was observed in almost all of the strains isolated from soil and horsehairs. In contrast, when an α-rich keratin substrate was used, the highest levels of hydrolysis were observed only for Ker39, Ker66, Ker85, Ker100, and Ker101. Strains with the highest biodegradation potential were identified using molecular biology methods. Phylogenetic analysis of 16S rDNA gene sequences allowed the assignment of selected keratinolytic microorganisms to the genera Exiguobacterium, Priestia, Curtobacterium, Stenotrophomonas, Bacillus, Kocuria, or Pseudomonas. The results of this study are a promising precursor for the development of new, more sustainable methods of managing keratin waste to produce high-value hydrolysates.

Strawberry Protease as a Laundry Detergent Additive Candidate: Immobilization, Compatibility Study with Detergent Ingredients, and Washing Performance Test

The potential of strawberry-derived protease as a component of laundry detergent is investigated. The compatibility of the enzyme with various surfactants, oxidizing agents, and commercial detergents is tested. The immobilized enzyme prepared by immobilizing Co2+ ions together with the enzyme is also tested. Strawberry crude protease shows high stability in the presence of surfactants frequently used in detergents. The enzyme is found to be relatively stable to oxidizing agents. In addition, it is determined that strawberry protease works in excellent compatibility with different commercial solid and liquid detergents in the Turkish market and also maintains its stability very well. Washing tests based on visual examination also reveal that the enzyme improves the washing performance of the tested detergent. All these properties and high activity at alkaline pH make this enzyme a very strong candidate for use in laundry detergent formulations.

Response surface methodology based optimization of keratinase from Bacillus velezensis strain ZBE1 and nanoparticle synthesis, biological and molecular characterization

The increasing demands of keratinases for biodegradation of recalcitrant keratinaceous waste like chicken feathers has lead to research on newer potential bacterial keratinases to produce high-value products with biological activities. The present study reports a novel keratinolytic bacterium Bacillus velezensis strain ZBE1 isolated from deep forest soil of Western Ghats of Karnataka, which possessed efficient feather keratin degradation capability and induced keratinase production. Production kinetics depicts maximum keratinase production (11.65 U/mL) on 4th day with protein concentration of 0.61 mg/mL. Effect of various physico-chemical factors such as, inoculum size, metal ions, carbon and nitrogen sources, pH and temperature influencing keratinase production were optimized and 3.74 folds enhancement was evidenced through response surface methodology. Silver (AgNP) and zinc oxide (ZnONP) nanoparticles with keratin hydrolysate produced from chicken feathers by the action of keratinase were synthesized and verified with UV-Visible spectroscopy that revealed biological activities like, antibacterial action against Bacillus cereus and Escherichia coli. AgNP and ZnONP also showed potential antioxidant activities through radical scavenging activities by ABTS and DPPH. AgNP and ZnONP revealed cytotoxic effect against MCF-7 breast cancer cell lines with IC50 of 5.47 µg/ml and 62.26 µg/ml respectively. Characterizations of nanoparticles were carried out by Fourier transform infrared spectroscopy, scanning electron microscopy with energy dispersive X-ray, X-ray diffraction, thermogravimetric analysis and atomic force microscopy analysis to elucidate the thermostability, structure and surface attributes. The study suggests the prospective applications of keratinase to trigger the production of bioactive value-added products and significant application in nanotechnology in biomedicine.

Synthesis and characterization of keratinase laden green synthesized silver nanoparticles for valorization of feather keratin

This study focuses on the efficient and cost-effective synthesis of silver nanoparticles (AgNPs) using plant extracts, which have versatile and non-toxic applications. The research objectives include synthesizing AgNPs from readily available plant extracts, optimizing their production and multi scale characterization, along with exploring their use for enzyme immobilization and mitigation of poultry feather waste. Among the plant extracts tested, the flower extract of Hibiscus rosa-sinensis (HF) showed the most potential for AgNP synthesis. The synthesis of HF-mediated AgNPs was optimized using response surface methodology (RSM) for efficient and environment friendly production. Additionally, the keratinase enzyme obtained from Bacillus sp. NCIM 5802 was covalently linked to AgNPs, forming a keratinase nanocomplex (KNC) whose biochemical properties were evaluated. The KNC demonstrated optimal activity at pH 10.0 and 60 °C and it displayed remarkable stability in the presence of various inhibitors, metal ions, surfactants, and detergents. Spectroscopic techniques such as FTIR, UV-visible, and X-ray diffraction (XRD) analysis were employed to investigate the formation of biogenic HF-AgNPs and KNC, confirming the presence of capping and stabilizing agents. The morphological characteristics of the synthesized AgNPs and KNC were determined using transmission electron microscopy (TEM) and particle size analysis. The study highlighted the antimicrobial, dye scavenging, and antioxidant properties of biogenic AgNPs and KNC, demonstrating their potential for various applications. Overall, this research showcases the effectiveness of plant extract-driven green synthesis of AgNPs and the successful development of keratinase-laden nanocomplexes, opening possibilities for their use in immobilizing industrial and commercial enzymes.

Biochemical and molecular characterization of novel keratinolytic protease from Bacillus licheniformis (KRLr1)

The keratin-degrading bacterium Bacillus licheniformis secretes a keratinase with potential industrial interest. Here, the Keratinase gene was intracellularly expressed in Escherichia coli BL21(DE3) using pET-21b (+) vector. Phylogenetic tree analysis showed that KRLr1 is closely related to Bacillus licheniformis keratinase that belongs to the serine peptidase/subtilisin-like S8 family. Recombinant keratinase appeared on the SDS-PAGE gel with a band of about 38 kDa and was confirmed by western blotting. Expressed KRLr1 was purified by Ni-NTA affinity chromatography with a yield of 85.96% and then refolded. It was found that this enzyme has optimum activity at pH 6 and 37°C. PMSF inhibited the KRLr1 activity and Ca²⁺ and Mg²⁺ increased the KRLr1 activity. Using keratin 1% as the substrate, the thermodynamic values were determined as K_m 14.54 mM, k_cat 912.7 × 10^-3 (S^-1), and k_cat/K_m 62.77 (M^-1 S^-1). Feather digestion by recombinant enzyme using HPLC method, showed that the amino acids cysteine, phenylalanine, tyrosine and lysine had the highest amount compared to other amino acids obtained from digestion. Molecular dynamics (MD) simulation of HADDOCK docking results exhibited that KRLr1 enzyme was able to interact strongly with chicken feather keratine 4 (FK4) compared to chicken feather keratine 12 (FK12). These properties make keratinase KRLr1 a potential candidate for various biotechnological applications.

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

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

Thermoactive metallo-keratinase from Bacillus sp. NFH5: Characterization, structural elucidation, and potential application as detergent additive

In recent times, robust green technological developments have advanced the goal of a circular economy by minimizing waste generation. The study was undertaken to explore the keratinolytic activity of chicken feather-degrading bacteria from South African soil. Isolates coded as SSN-01 and HSN-01 were identified as Bacillus sp. NFH5 and Bacillus sp. FHNM and their sequences were deposited in GenBank, with accession numbers MW165830.1 and MW165831.1, respectively. Extracellular enzyme production and thiol group generation by Bacillus sp. NFH5 peaked at 120 h with 1879.09 ± 88.70 U/mL and 9.49 ± 0.78 mM, respectively. Glutamic acid (4.44%), aspartic acid (3.50%), arginine (3.23%), glycine (2.61%), serine (2.08%), and proline (2.08%) were relatively higher in concentration. Keratinase (KerBAN) activity was highest at pH 8.0 and 90 °C but was inhibited by both EDTA and 1,10-phenanthroline. In addition, the keratinase-encoding gene (kerBAN) accessioned OK033360 had 362 amino acid residues, with molecular weight and theoretical isoelectric point of 39 kDa and 8.81, respectively. Findings from this study highlight the significance of Bacillus sp. NFH5 in the bio-recycling of recalcitrant keratinous wastes to protein hydrolysates - potential dietary supplements for livestock feeds. The properties of KerBAN underscore its application potential in green biotechnological processes.

Keratinolytic Properties of Aspergillus clavatus Promising for Biodegradation

The high demand for keratinolytic enzymes and the modest presentation of fungal keratinase diversity studies in scientific sources cause a significant interest in identifying new fungal strains of keratinase producers, isolating new enzymes and studying their properties. Four out of the 32 cultures showed a promising target activity on protein-containing agar plates-Aspergillus amstelodami A6, A. clavatus VKPM F-1593, A. ochraceus 247, and Cladosporium sphaerospermum 1779. The highest values of keratinolytic activity were demonstrated by extracellular proteins synthesized by Aspergillus clavatus VKPM F-1593 cultivated under submerged conditions on a medium containing milled chicken feathers. The enzyme complex preparation was obtained by protein precipitation from the culture liquid with ammonium sulfate, subsequent dialysis, and lyophilization. The fraction of a pure enzyme with keratinolytic activity (pI 9.3) was isolated by separating the extracellular proteins of A. clavatus VKPM F-1593 via isoelectric focusing. The studied keratinase was an alkaline subtilisin-like non-glycosylated protease active over a wide pH range with optimum keratinolysis at pH 8 and 50 °C.