Microbial production and industrial applications of keratinases: an overview

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.

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.

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

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

Biodegradation and valorization of feather waste using the keratinase-producing bacteria and their application in environmentally hazardous industrial processes

Poultry feathers are widely discarded as waste worldwide and are considered an environmental pollutant and a reservoir of pathogenic bacteria. Therefore, developing sustainable and environmentally friendly methods for managing feather waste is one of the important environmental protection requirements. In this study, we investigated a rapid and eco-friendly method for the degradation and valorization of feather waste using keratinase-producing Pseudomonas geniculata H10, and evaluated the applicability of keratinase in environmentally hazardous chemical processes. Strain H10 completely degraded chicken feathers within 48 h by producing keratinase using them as sources of carbon, nitrogen, and sulfur. The culture contained a total of 402.8 μM amino acids, including 8 essential amino acids, which was higher than the chemical treatment. Keratinase was a serine-type metalloprotease with optimal temperature and pH of 30 °C and 9, respectively, and showed relatively high stability at 10-40 °C and pH 3-10. Keratinase was also able to degrade various insoluble keratins such as duck feathers, wool, human hair, and nails. Furthermore, keratinase exhibited more efficient depilation and wool modification than chemical treatment, as well as novel functionalities such as nematicidal and exfoliating activities. This suggests that strain H10 is a promising candidate for the efficient degradation and valorization of feather waste, as well as the improvement of current industrial processes that use hazardous chemicals.

Heavy Metals in Vegetables: Screening Health Risks of Irrigation with Wastewater in Peri-Urban Areas of Bhakkar, Pakistan

One of the key concerns in public health is food security in the food sector. Due to the large amounts of potentially hazardous metals in wastewater, this practice may pose serious environmental and health risks to neighboring residents. In this study, the health effects of heavy metals in vegetables irrigated with wastewater were studied. The findings indicated a massive accumulation of heavy metals in wastewater-irrigated soil and vegetables collected from Bhakkar, Pakistan. The current study looked at the effects of wastewater irrigation on metal buildup in the soil-plant continuum and the health hazards that come with it (Cd, Co, Ni, Mn, Pb, and Fe). Heavy metal concentrations in vegetables cultivated on soil irrigated with untreated wastewater were not significantly lower (p ≥ 0.05) than in vegetables grown on wastewater-irrigated soil and were below the World Health Organization's recommended limits. A considerable amount of the selected hazardous metals was also swallowed by adults and children who consumed these vegetables, according to the research. On soil that had received wastewater irrigation, Ni and Mn were substantially different at p ≥ 0.001 levels. Pb, Ni, and Cd had health risk scores higher than the ones in all ingested vegetables, while Mn had a health risk score greater than the ones in turnips, carrots, and lettuce. The results also showed that both adults and children who consumed these vegetables absorbed a significant amount of the chosen toxic metals. Pb and Cd were shown to be the most dangerous chemical compounds to human health, and everyday consumption of agricultural plants irrigated with wastewater may pose a health risk, according to the health risk criteria.

Microalgal-induced remediation of wastewaters loaded with organic and inorganic pollutants: An overview

The recent surge in industrialization has intensified the accumulation of various types of organic and inorganic pollutants due to the illegal dumping of partially and/or untreated wastewater effluents in the environment. The pollutants emitted by several industries pose serious risk to the environment, animals and human beings. Management and diminution of these hazardous organic pollutants have become an incipient research interest. Traditional physiochemical methods are energy intensive and produce secondary pollutants. So, bioremediation via microalgae has appeared to be an eco-friendly and sustainable technique to curb the adverse effects of organic and inorganic contaminants because microalgae can degrade complex organic compounds and convert them into simpler and non-toxic substances without the release of secondary pollutants. Even some of the organic pollutants can be exploited by microalgae as a source of carbon in mixotrophic cultivation. Literature survey has revealed that use of the latest modification techniques for microalgae such as immobilization (on alginate, carrageena and agar), pigment-extraction, and pretreatment (with acids) have enhaced their bioremedial potential. Moreover, microalgal components i.e., biopolymers and extracellular polymeric substances (EPS) can potentially be exploited in the biosorption of pollutants. Though bioremediation of wastewaters by microalgae is quite well-studied realm but some aspects like structural and functional responses of microalgae toward pollutant derivatives/by-products (formed during biodegradation), use of genetic engineering to improve the tolerance of microalgae against higher concentrations of polluatans, and harvesting cost reduction, and monitoring of parameters at large-scale still need more focus. This review discusses the accumulation of different types of pollutants into the environment through various sources and the mechanisms used by microalgae to degrade commonly occurring organic and inorganic pollutants.

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.

Exploring the Potential Applications of Paecilomyceslilacinus 112

Microorganisms are widely used to obtain biostimulants that can facilitate the assimilation of nutrients, ensuring high crop yield and quality. A particular category of biostimulants are protein hydrolyzates (PH), obtained from microbial cultures grown on a nutrient medium. In the present study, Paecilomyces lilacinus 112, an endophytic fungus isolated from soil, was tested to determine its effect on the growth promotion of tomato seedlings in greenhouse conditions. Additionally, other beneficial features of the P.lilacinus isolate were evaluated via several tests: antagonism against plant pathogenic fungi, production of secondary useful metabolites, and solubilization of vital micronutrients. Out of the tested pathogens, P.lilacinus exhibited the highest antifungal activity against a Cladosporium isolate (inhibition of 66.3%), followed by Rhizoctonia. solani (52.53%), and Sclerotinia sclerotiorum (50.23%). Paecilomyceslilacinus 112 was able to secrete hydrolytic enzymes and siderophores, and solubilize zinc and phosphorus. In the tomato treatment, the application of PH obtained from fungal cultivation on a feather medium led to the following increases in plant growth parameters: 3.54-fold in plant biomass; 3.26-fold in plant height, 1.28-fold in plant diameter; 1.5-fold in the number of branches/plant; and 1.43-fold in the number of leaves/plant, as compared to water treatment. The application of this isolate can be of benefit to bioeconomy because keratin wastes are valorized and returned, in agriculture, contributing to renewable natural resources.

Enhanced keratinase production by Bacillus subtilis amr using experimental optimization tools to obtain feather protein lysate for industrial applications

The poultry industry produces millions of tons of feathers waste that can be transformed into valuable products through bioprocess. The study describes the enhanced keratinase and feather hydrolysate production by Bacillus subtilis AMR. The metabolism of each microorganism is unique, so optimization tools are essential to determine the best fermentation parameters to obtain the best process performance. The evaluation of different propagation media indicated the constitutive production of two keratinases of approximately 80 kDa. The combination of Mn²⁺, Ca²⁺, and Mg²⁺ at 0.5 mM improved the keratinolytic activity and feather degradation 1.5-fold, while Cu²⁺ inhibited the enzymatic activity completely. Replace yeast extract for sucrose increased the feather hydrolysate production three times. The best feather concentration for hydrolysate production was 1.5% with an inoculum of 10⁸ CFU/mL and incubation at 30 °C. None of the inorganic additional nitrogen sources tested increased hydrolysate production, although (NH₄)₂SO₄ and KNO₃ improved enzymatic activity. The optimization process improved keratinolytic activity from 205.4 to 418.7 U/mL, the protein concentration reached 10.1 mg/mL from an initial concentration of 3.9 mg/mL, and the feather degradation improved from 70 to 96%. This study characterized keratinase and feather hydrolysate production conditions offering valuable information for exploring and utilizing AMR keratinolytic strain for feather valorization.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-022-03153-y.

Enhancement of Activity and Thermostability of Keratinase From Pseudomonas aeruginosa CCTCC AB2013184 by Directed Evolution With Noncanonical Amino Acids

A keratinase from Pseudomonas aeruginosa (KerPA), which belongs to the M4 family of metallopeptidases, was characterised in this study. This enzyme was engineered with non-canonical amino acids (ncAAs) using genetic code expansion. Several variants with enhanced activity and thermostability were identified and the most prominent, Y21pBpF/Y70pBpF/Y114pBpF, showed an increase in enzyme activity and half-life of approximately 1.3-fold and 8.2-fold, respectively. Considering that keratinases usually require reducing agents to efficiently degrade keratin, the Y21pBpF/Y70pBpF/Y114pBpF variant with enhanced activity and stability under reducing conditions may have great significance for practical applications. Molecular Dynamics (MD) was performed to identify the potential mechanisms underlying these improvements. The results showed that mutation with pBpF at specific sites of the enzyme could fill voids, form new interactions, and reshape the local structure of the active site of the enzyme.

Biodegradation of Keratin-Rich Husbandry Waste as a Path to Sustainable Agriculture

Every year, the size of the human population grows; with it, the need for agricultural products increases. This leads to an increment in the volume of waste, including hard-to-degrade keratin-rich ones, such as feathers. Currently, most of the agro-industrial complex protein by-products are utilized by incineration, landfilling, and chemical hydrolysis. Such methods do not meet modern trends in the development of a sustainable economy, negatively affecting the environment and humans, and preventing the reusing of waste. An alternative is biodegradation, which consists of the application of living organisms and their enzymes to recycle by-products. This approach is not only sustainable, but also makes it possible to obtain products of waste hydrolysis that are in demand for the manufacture of fertilizers and feed additives. This brings the development of agriculture closer to a circular economy and makes the recycling process more profitable. This review article emphasizes the significance of keratinolytic microorganisms and keratinases for the improvement of green methods for processing hard-to-degrade protein waste of the agro-industrial complex, which is necessary for sustainable economic development.

Fungal decomposition of chicken-feather waste in submerged and solid-state fermentation

Poultry industry is expanding rapidly and producing million tons of feather waste annually. Massive production of keratinaceous byproducts in the form of industrial wastes throughout the world necessitates its justified utilization. Chemical treatment of keratin waste is proclaimed as an eco-destructive approach by various researchers since it generates secondary pollutants. Keratinase released by a variety of microbes (bacteria and fungi) can be used for the effective treatment of keratin waste. Microbial degradation of keratin waste is an emerging and eco-friendly approach and offers dual benefits, i.e., treatment of recalcitrant pollutant (keratin) and procurement of a commercially important enzyme (keratinase). This study involves the isolation, characterization, and potential utility of fungal species for the degradation of chicken-feather waste through submerged and solid-state fermentation. The isolated fungus was identified and characterized as Aspergillus (A.) flavus. In a trial of 30 days, it was appeared that 74 and 8% feather weight was reduced through sub-merged and solid-state fermentation, respectively by A. flavus. The pH of the growth media in submerged fermentation was changed from 4.8 to 8.35. The exploited application of keratinolytic microbes is, therefore, recommended for the treatment of keratinaceous wastes to achieve dual benefits of remediation.

A Thermostable Aluminum-Tolerant Protease Produced by Feather-Degrading Bacillus thuringiensis Isolated from Tea Plantation

BACKGROUND

Proteases with keratinolytic activity are widely used in biotechnologies. The feather-degrading Bacillus thuringensis isolated from soil sample of a tea plantation produced high level of extracellular keratinase.

OBJECTIVE

This study aimed to analyze the properties by biochemical and enzymological methods to gain information for better utilization of the enzyme.

METHODS

The enzyme was purified with ion exchange and size exclusion chromatography. The substrate preference, optimal pH and temperature, and the effects of organic solvents and ions were checked. Circular dichroism was performed to compare the secondary structures of the native and apo-enzyme.

RESULTS

The enzyme worked best at 50°C, and it was an acidic serine protease with an optimal pH of 6.2. Ions Ca²⁺ and Mg²⁺ were essential for its activity. Organic solvents and other metal ions generally deactivated the enzyme in a concentration-dependent manner. However, Mn²⁺ and DMSO, which were frequently reported as inhibitors of protease, could activate the enzyme at low concentration (0.01 to 2 mmol/L of Mn²⁺; DMSO <2%, v/v). The enzyme exhibited high resistance to Al³⁺, which might be explained by the soil properties of its host's residence. Circular dichroism confirmed the contribution of ions to the structure and activity.

CONCLUSION

The enzyme was a thermostable aluminum-tolerant serine protease with unique biochemical properties.

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

Keratinases are unique among proteolytic enzymes for their ability to degrade recalcitrant insoluble proteins, and they are of critical importance in keratin waste management. Over the past few decades, researchers have focused on discovering keratinase producers, as well as producing and characterizing keratinases. The application potential of keratinases has been investigated in the feed, fertilizer, leathering, detergent, cosmetic, and medical industries. However, the commercial availability of keratinases is still limited due to poor productivity and properties, such as thermostability, storage stability and resistance to organic reagents. Advances in molecular biotechnology have provided powerful tools for enhancing the production and functional properties of keratinase. This critical review systematically summarizes the application potential of keratinase, and in particular certain newly discovered catalytic capabilities. Furthermore, we provide comprehensive insight into mechanistic and molecular aspects of keratinases including analysis of gene sequences and protein structures. In addition, development and current advances in protein engineering of keratinases are summarized and discussed, revealing that the engineering of protein domains such as signal peptides and pro-peptides has become an important strategy to increase production of keratinases. Finally, prospects for further development are also proposed, indicating that advanced protein engineering technologies will lead to improved and additional commercial keratinases for various industrial applications.

Production and characterization of keratinase by Ochrobactrum intermedium for feather keratin utilization

A newly isolated bacterium producing 55.5 U/mL keratinase on feather meal minimal medium was identified as Ochrobactrum intermedium. Optimization of process parameters by one-variable-at-a-time (OVAT) approach (substrate concentration 0.5% w/v, inoculum size 5% w/v, pH 7.0, 200 rpm for 96 h at 40 °C) resulted in 2.1-fold increase in keratinase secretion (117 U/mL). Keratinase was optimally active at pH 9.0 and 40 °C and was stable at pH 9.0 and 60 °C for 120 min. Calcium ions enhanced keratinase activity (158%) significantly, while it was strongly inhibited by both PMSF and EDTA, indicating it to be a metallo-serine protease. Keratinase degraded native chicken feathers efficiently resulting in 97.9% weight loss along with release of 745.5 μg/mL soluble proteins and 4196.69 μg/mL amino acids. Feather hydrolysate generated by NKIS 1 exhibited significant anti-oxidant and free-radical scavenging activity (90.46%). The present study revealed that O. intermedium NKIS 1 has potential applications in the biodegradation of chicken feathers and the value-addition of poultry waste.

The extremophile Anoxybacillus sp. PC2 isolated from Brazilian semiarid region (Caatinga) produces a thermostable keratinase

The aim of this study was to select and identify thermophilic bacteria from Caatinga biome (Brazil) able to produce thermoactive keratinases and characterize the keratinase produced by the selected isolate. After enrichment in keratin culture media, an Anoxybacillus caldiproteolyticus PC2 was isolated. This thermotolerant isolate presents a remarkable feature producing a thermostable keratinase at 60°C. The partially purified keratinase, identified as a thermolysin-like peptidase, was active at a pH range of 5.0-10.0 with maximal activity at a temperature range of 50-80°C. The optimal activity was observed at pH 7.0 and 50-60°C. These characteristics are potentially useful for biotechnological purposes such as processing and bioconversion of keratin.

Enhancement of keratin-degradation ability of the keratinase KerBL from Bacillus licheniformis WHU by proximity-triggered chemical crosslinking

Keratinases are valuable enzymes, given their application in keratin-rich waste recycling. Considering that keratinases usually require reducing agents to efficiently degrade keratin, improving the stability of keratinases under reducing conditions is highly desirable for practical applications. Here, we show that the introduction of several tyrosine derivatives containing para-substituted long-chain haloalkanes into the keratinase KerBL, which enabled proximity-triggered covalent crosslinking by rational design, could improve both the thermostability and autolytic resistance of the enzyme. After screening a series of noncanonical amino acid (ncAA)-based variants generated by rational design, two variants, N159C/Y260BprY and N159C/Y260BbtY, with enhanced keratinolytic activity were obtained. Both variants increased the T_m of the enzyme by approximately 10 °C. The potential mechanism underlying these improvements was investigated by molecular dynamics (MD) analysis. The results indicated that BprY-Cys and BbtY-Cys covalent bonds in the N159C/Y260TAG variant could significantly decrease the flexibility and fluctuations of the long loop (residues 151-162).

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.

Recombinant expression and molecular engineering of the keratinase from Brevibacillus parabrevis for dehairing performance

Keratinase is capable of distinctive degradation of keratin, which provides an eco-friendly approach for keratin waste management towards sustainable development. In this study, the recombinant keratinase (KERBP) from Brevibacillus parabrevis was successfully expressed in Escherichia coli. The purified KERBP had the specific activity of 6005.3 U/mg. It showed remarkable tolerance to various surfactants and also no collagenolytic activity. However, the moderate thermal stability limited its further application. Thus, protein engineering was further adopted to improve its stability. The variants of T218S, S236C and N181D were constructed by site-directed mutagenesis and combinatorial mutagenesis. Compared with the wild type, the t_1/2 at 60 °C for the variants T218S, S236C and N181D were 3.05-, 1.18- and 1-fold increase, respectively. Moreover, the double variants N181D-T218S and N181D-S236C significantly improved thermostability with 5.1 and 2.9 °C increase of T₅₀, and prolonging t_1/2 at 60 °C with 4.09 and 1.54-fold, respectively. And the catalytic efficiency of the T218S and N181D-T218S variants was also significantly improved. Furthermore, the keratinase displayed favorable ability to dehair wool from skin within 7 h, which showed potential in leather dehairing. Our work contributes to a further insight into the thermostability of keratinase and offers a promising alternative for industrial leather application.

Biochemical characterisation and application of keratinase from Bacillus thuringiensis MT1 to enable valorisation of hair wastes through biosynthesis of vitamin B-complex

This study reports on the exploitation of keratinous hydrolysate by keratinase enzymes to produce vitamin B-complex. Toward this end, keratinase enzyme was produced by Bacillus thuringiensis strain MT1, newly isolated from cattle-yard utilising donkey hairs. Scanning electron microscope (SEM) and Fourier transform infrared spectrophotometer (FTIR) analyses demonstrated hairs disintegration and the disruption of the disulphide bonds of the keratin structure, respectively. The biochemical characterisation of the produced enzyme exhibited optimal activity of 422 U/ml at 50 °C and pH 9 with a molecular mass of 80 kDa. The enzyme activity was entirely deactivated by Ethylenediaminetetraacetic acid (EDTA), implying the existence of a metallokeratinase group. Donkey hairs were thus treated with metallokeratinase, emancipating eight essential and eight more non-essential amino acids, which were identified employing amino acid analyser. These amino acids were subsequently utilised by Saccharomyces cerevisiae strain ATCC 64712, at different concentrations, to produce vitamin B-complex. High-performance liquid chromatography (HPLC) analysis revealed the synthesis of vitamins B1, B2, and B12 at various levels associated with concentrations of supplemented amino acids. This report thus highlights the feasible application of keratinase enzyme as an eco-friendly approach to managing hair waste, and concurrently promotes the implementation of hair-based hydrolysate in vitamin B-complex biosynthesis.

Microbial Bioremediation of Feather Waste for Keratinase Production: An Outstanding Solution for Leather Dehairing in Tanneries

In leather industries and tanneries, large amount of wastes has been disposed; which polluting water, soil, and atmosphere and causing serious human health problems. In particular, chemical dehairing process of leather industries produces fair amount of toxic wastes. It is, thus, urgently needed to use alternative processes free from pollution. As more than 90% of keratin is contained in feather, it is desirable to develop bioremediation process using keratinolytic microorganisms. In the present investigation, therefore, we first identified Bacillus cereus and Pseudomonas sp. to be able to produce keratinase. Then, the optimization was performed to maximize the keratinase activity with respect to cultivation temperature, pH, and incubation time. Moreover, the effects of metal ions and various substrates on keratinase activity were also investigated. The result indicates that keratinase activity became maximum at 50°C for both strains, whereas the optimal pH was 10.0 for B. cereus and 7.0 for Pseudomonas sp. The highest keratinase activity of 74.66 ± 1.52 U/mL was attained by B. cereus, whereas 57.66 ± 2.52 U/mL was attained by Pseudomonas sp. Enzymatic dehairing efficiency of leathers was also compared with chemical dehairing (Na₂S and CaO), where complete dehairing was achieved by treating them with crude keratinase. Partial enzyme purification was performed by acetone precipitation. Batch cultivation of B. cereus using 1 L fermentor indicates a potential candidate for large-scale keratinase production. Thus, keratinase enzyme by degrading poultry wastes (feather) can be an alternative approach to chemical dehairing in leather industries, thus preventing environmental pollution through bioremediation.

Selective biodegradation of recalcitrant black chicken feathers by a newly isolated thermotolerant bacterium Pseudochrobactrum sp. IY-BUK1 for enhanced production of keratinase and protein-rich hydrolysates

Black chicken feathers generated in large amount from poultry and slaughter houses are highly recalcitrant to microbial degradation due to their tough structural nature. A novel keratinolytic bacterium that possessed high affinity for black feather was isolated from chicken manure and identified as Pseudochrobactrum sp. IY-BUK1. Keratinase and feather soluble protein were effectively produced by the free living cells of the bacterium in media containing only black feathers and a mixture of equal amount of black-, brown- and white-coloured feathers. Complete degradation of 5 g/L of black feathers was completed in 3 days following optimisation of physico-chemical conditions. However, the bacterium selectively completed the degradation of black feather in a medium containing mixture of feathers in 144 h leaving behind approximately 33% and 45% of brown and white feathers in the medium respectively. Gellan gum-immobilised cells of strain IY-BUK1 enhanced the keratinase production by about 150% and were used repeatedly for ten cycles to degrade 5 g/L of black feather in a semi continuous fermentation of 18 h per cycle with enhanced and stable production of soluble protein. The study demonstrated the potential use of Pseudochrobactrum sp. IY-BUK1 not only in biodegradation of highly recalcitrant black feathers, but also in producing keratinase enzymes and valuable soluble proteins for possible industrial usage.

Microbial Degradation of Pesticide Residues and an Emphasis on the Degradation of Cypermethrin and 3-phenoxy Benzoic Acid: A Review

Nowadays, pesticides are widely used in preventing and controlling the diseases and pests of crop, but at the same time pesticide residues have brought serious harm to human's health and the environment. It is an important subject to study microbial degradation of pesticides in soil environment in the field of internationally environmental restoration science and technology. This paper summarized the microbial species in the environment, the study of herbicide and pesticides degrading bacteria and the mechanism and application of pesticide microbial degrading bacteria. Cypermethrin and other pyrethroid pesticides were used widely currently, while they were difficult to be degraded in the natural conditions, and an intermediate metabolite, 3-phenoxy benzoic acid would be produced in the degradation process, causing the secondary pollution of agricultural products and a series of problems. Taking it above as an example, the paper paid attention to the degradation process of microorganism under natural conditions and factors affecting the microbial degradation of pesticide. In addition, the developed trend of the research on microbial degradation of pesticide and some obvious problems that need further solution were put forward.