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.

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.

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.

Approach towards sustainable leather: Characterization and effective industrial application of proteases from Bacillus sps. for ecofriendly dehairing of leather hide

Tanneries are one of the most polluted industries known for production of massive amount of solid and liquid wastes without proper management and disposal. In this project we demonstrated the ecofriendly single step dehairing of leather hides with minimum pollution load. In this study, Bacillus species (Bacillus paralicheniformis strain BL.HK, Bacillus cereus strain BS.P) capable of producing proteases was successfully isolated by employing the new optimized selective media named M9-PEA as confirmed by 16sRNA genes sequencing. Sequence of 1493 bp long 16S rRNA genes of Bacillus paralicheniformis strain BL.HK and Bacillus cereus strain BS. P was submitted to GenBank under the accession number OP612692.1, OP612721.1 respectively The Bacillus paralicheniformis strain BL.HK, Bacillus cereus strain BS.P produced extracellur proteases of 28 and 37 KDa as resolved by SDS-PAGE respectively. The enzymes showed temperature optima at 50 °C and 55 °C and pH optima at 8.5, 9.5 respectively. The Proteases of Bacillus paralicheniformis strain BL.HK, Bacillus cereus strain BS.P were employed for dehairing of animal hides. The process resulted in significant removal of interfibriller substances without damage to collagen layer after one hour treatment, which was confirmed by histology, scanning electron microscopy. The quantification of various skin constituents (collagen, uronic acid, hexosamines, and GAGs) and pollution load parameters revealed that enzymatic treatment are more reliable. The results of skin application trials at industrial level with complete elimination of chemicals remark the biotechnological potential of these proteases for ecofriendly dehairing of animal hides without affecting the quality of the leathers produced.

Research progress on the degradation mechanism and modification of keratinase

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

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.

Production and characterization of a new detergent-stable keratinase expressed by Pedobacter sp. 3.14.7, a novel Antarctic psychrotolerant keratin-degrading bacterium

BACKGROUND

Antarctica is one of the harshest environments in the world. Despite this fact, it has been colonized by microorganisms, which had to develop different adaptations in order to survive. By studying their enzymes, we can harness these adaptations in order to use them in various industrial processes. Keratinases (E.C. 3.4.99.11) are characterized by their robustness in withstanding extreme conditions and, along with other enzymes, are commonly added to laundry detergents, which makes their study of industrial interest.

RESULTS

In this work, a novel keratinase producer, Pedobacter sp. 3.14.7 (MF 347939.1), isolated from Antarctic birds' nests, was identified. This psychrotolerant isolate displays a typical psychrotolerant growth pattern, with an optimal temperature of 20 °C (μmax=0.23 h^-1). After 238 h, maximum proteolytic (22.00 ± 1.17 U ml^-1) and keratinolytic (33.04 ± 1.09 U ml^-1) activities were achieved with a feather sample conversion of approximately 85%. The keratinase present in crude extract was characterized as a metalloprotease with a molecular weight of 25 kDa, stable in a wide range of pH, with an optimum pH of 7.5. Optimum temperature was 55 °C. Wash performance at 20 °C using this crude extract could remove completely blood stain from cotton cloth.

CONCLUSION

We report a new keratinolytic bacteria from maritime Antarctica. Among its biochemical characteristics, its stability in the presence of different detergents and bleaching agents and its wash performance showed promising results regarding its potential use as a laundry detergent additive.

Isolation of Bacillus sp. A5.3 Strain with Keratinolytic Activity

Simple Summary

In this study, we described keratinolytic properties of a strain of Bacillus (sp. A5.3) isolated from sites of feather waste accumulation. The proteolytic enzymes secreted by Bacillus sp. A5.3 are serine proteases, are alkaline enzymes, have a wide substrate specificity, and have high thermal stability. Bacillus sp. A5.3 effectively hydrolyzes feathers and can be used in feather-processing technologies and as a source of alkaline and thermostable proteases and keratinases.

Abstract

Environmental safety and economic factors necessitate a search for new ways of processing poultry farm feathers, which are 90% β-keratin and can be used as a cheap source of amino acids and peptones. In this study, feather-decomposing bacteria were isolated from a site of accumulation of rotten feathers and identified as Bacillus. Among them, the Bacillus sp. A5.3 isolate showed the best keratinolytic properties. Scanning electron microscopy indicated that Bacillus sp. A5.3 cells closely adhere to the feather surface while degrading the feather. It was found that Bacillus sp. A5.3 secretes thermostable alkaline proteolytic and keratinolytic enzymes. Zymographic analysis of the enzymatic extract toward bovine serum albumin, casein, gelatin, and β-keratin revealed the presence of proteases and keratinases with molecular weights 20–250 kDa. The proteolytic and keratinolytic enzymes predominantly belong to the serine protease family. Proteome analysis of the secreted proteins by nano-HPLC coupled with Q-TOF mass spectrometry identified 154 proteins, 13 of which are proteases and peptidases. Thus, strain Bacillus sp. A5.3 holds great promise for use in feather-processing technologies and as a source of proteases and keratinases.

Bacillus amyloliquefaciens 35 M can exclusively produce and secrete proteases when cultured in soybean-meal-based medium

Some microbial strains are ideal producers of extracellular enzymes that can be used in various industries. However, in many fields, especially in the pharmaceutical field, these enzymes need to be recovered and purified through multistep processes and tedious procedures before they can be used. The recovery process is difficult and increases the cost of enzyme production. Therefore, reducing purification steps will greatly benefit the utilization of microbial enzymes. The 35 M strain of Bacillus amyloliquefaciens, which has high extracellular protease production, was isolated from a phosphate mine. When cultured in a medium with soybean meal as the main component, the maximum activity of extracellular protease reached 16,992 U/mL. SDS-PAGE showed that there were two main proteins in the fermentation supernatant, with a paucity of other defined protein bands. Mass spectrometry and zymogram analysis showed that the two main bands were two proteases, corresponding to alkaline protease (AprM) and neutral protease (NprM), respectively. Gene cloning, sequencing, and further comparisons were used to confirm AprM and NprM correspond to these proteases from B. amyloliquefaciens. Notably, SDS-PAGE and zymogram analysis showed that NprM had obviously higher catalytic efficiency toward casein than did AprM. Strain 35 M is a promising protease producer with great potential for applications in industrial protease production. Additionally, this study demonstrates strain 35 M may be particularly well suited to use in degrading anti-nutritional factors in soybean meal, so as to improve the nutritional value of soybean meal.

Keratinases as Versatile Enzymatic Tools for Sustainable Development

To reduce anthropological pressure on the environment, the implementation of novel technologies in present and future economies is needed for sustainable development. The food industry, with dairy and meat production in particular, has a significant environmental impact. Global poultry production is one of the fastest-growing meat producing sectors and is connected with the generation of burdensome streams of manure, offal and feather waste. In 2020, the EU alone produced around 3.2 million tonnes of poultry feather waste composed primarily of keratin, a protein biopolymer resistant to conventional proteolytic enzymes. If not managed properly, keratin waste can significantly affect ecosystems, contributing to environmental pollution, and pose a serious hazard to human and livestock health. In this article, the application of keratinolytic enzymes and microorganisms for promising novel keratin waste management methods with generation of new value-added products, such as bioactive peptides, vitamins, prion decontamination agents and biomaterials were reviewed.

Improvement of the halotolerance of a Bacillus serine protease by protein surface engineering

A moderately halotolerant serine protease was previously isolated from Bacillus subtilis from salted, fermented food. Eight mutation sites on the protein surface were selected for protein engineering based on sequence and structural comparisons with moderately halotolerant proteases and homologous non-halotolerant proteases. The newly constructed multiple mutants with substituted Asp and Arg residues were compared with the recombinant wild type (rApr) and the previously constructed mAla-8 substituted with Ala to analyze the contribution of protein surface charge to the salt adaptation of the protease. The three mutants showed >1.2-fold greater halotolerance than rApr. In addition, the mutants showed a broader range of pH stability than rApr, retaining >80% of their maximum activity in the pH range 5.0-11. The mutants also retained >75% of their activity after incubation for 1 h at pH 8.0 and 55°C or at pH 11.5 and 25°C. The Asp and Arg residues exchanged by multiple substitution probably played a role in increasing protein surface hydration and solubility in high salt conditions. This study illustrated that increasing a high proportion of the negative or positive charge on the surface of the Bacillus serine protease stably improved the protein's salt adaptation.

The keratinolytic bacteria Bacillus cytotoxicus as a source of novel proteases and feather protein hydrolysates with antioxidant activities

BACKGROUND

Argentina's geothermal areas are niches of a rich microbial diversity. In 2020, species of Bacillus cytotoxicus were isolated for the first time from these types of pristine natural areas. Bacillus cytotoxicus strains demonstrated the capability to grow and degrade chicken feathers with the concomitant production of proteases with keratinolytic activity, enzymes that have multitude of industrial applications. The aim of this research was to study the production of the proteolytic enzymes and its characterization. Also, feather protein hydrolysates produced during fermentation were characterized.

RESULTS

Among the thermotolerant strains isolated from the Domuyo geothermal area (Neuquén province, Argentina), Bacillus cytotoxicus LT-1 and Oll-15 were selected and put through submerged cultures using feather wastes as sole carbon, nitrogen, and energy source in order to obtain proteolytic enzymes and protein hydrolysates. Complete degradation of feathers was achieved after 48 h. Zymograms demonstrated the presence of several proteolytic enzymes with an estimated molecular weight between 50 and > 120 kDa. Optimum pH and temperatures of Bacillus cytotoxicus LT-1 crude extract were 7.0 and 40 °C, meanwhile for Oll-15 were 7.0 and 50 °C. Crude extracts were inhibited by EDTA and 1,10 phenanthroline indicating the presence of metalloproteases. Feather protein hydrolysates showed an interesting antioxidant potential measured through radical-scavenging and Fe³⁺-reducing activities.

CONCLUSION

This work represents an initial approach on the study of the biotechnological potential of proteases produced by Bacillus cytotoxicus. The results demonstrated the importance of continuous search for new biocatalysts with new characteristics and enzymes to be able to cope with the demands in the market.

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.

Optimization and validation of keratinase production by Bacillus aerius NSMk2 in a stirred tank reactor using response surface methodology

Abstract

Keratinase is a robust enzyme that is produced in the presence of keratin substrates. This enzyme has been recognized for its applications in waste management, leather and detergent industries. Our group has isolated a potential keratinase producing strain of Bacillus aerius NSMk2 from poultry dump soil, and its hide dehairing and stain removal applications have been studied. Considering commercial applicability of keratinase, the present study reports the keratinase production in a stirred tank reactor (5 l). Central composite rotatable design of response surface methodology (RSM) was employed to study the effect of most influencing process variables, i.e., aeration (0.5–1.5 vvm), agitation (150–350 rpm) and incubation period (24–48 h) on keratinase production. The quadratic model predicted 15 experimental runs, and the influence of independent variables and their interaction on keratinase production were interpreted using analysis of variance (ANOVA) and t-test statistics. Coefficient of determination (R2) value close to 1 and Fisher F-value of 3743.77 showed good fit of experimental data to second-order polynomial equation. A reasonable agreement between experimental and predicted values showed the accuracy of deduced model. Applying the desirability function, aeration rate of 1.0 vvm, agitation rate of 276.88 rpm and incubation period of 33.68 h supported maximum keratinase production (318.38 U/ml). Confirmatory experiments were performed to evaluate the accuracy of desirability function. Maximum keratinase activity of 318.11 U/ml close to predicted value (318.38 U/ml) validates the model. The present study provides useful guidelines for large-scale production of keratinase that can be used for various commercial applications.

Article highlights

Chicken Feather Waste Hydrolysate as a Superior Biofertilizer in Agroindustry

Billions of tons of keratinous waste in the form of feathers, antlers, bristles, claws, hair, hoofs, horns, and wool are generated by different industries and their demolition causes environmental deterioration. Chicken feathers have 92% keratin that can be a good source of peptides, amino acids, and minerals. Traditional methods of feather hydrolysis require large energy inputs, and also reduce the content of amino acids and net protein utilization values. Biological treatment of feathers with keratinolytic microbes is a feasible and environmental favorable preference for the formulation of hydrolysate that can be used as bioactive peptides, protein supplement, livestock feed, biofertilizer, etc. The presence of amino acids, soluble proteins, and peptides in hydrolysate facilitates the growth of microbes in rhizosphere that promotes the uptake and utilization of nutrients from soil. Application of hydrolysate enhances water holding capacity, C/N ratio, and mineral content of soil. The plant growth promoting activities of hydrolysate potentiates its possible use in organic farming, and improves soil ecosystem and microbiota. This paper reviews the current scenario on the methods available for management of keratinous waste, nutritional quality of hydrolysate generated using keratinolytic microbes, and its possible application as plant growth promoter in agroindustry.

Identification of a Novel Thermostable Alkaline Protease from Bacillus megaterium-TK1 for the Detergent and Leather Industry

Simple Summary

In the current investigation, we describe the characteristic features of a novel Bacillus megaterium bacterium-derived protease with excellent thermostable enzyme activity under stringent alkaline conditions. The protease is highly compatible with various detergents and thus appears to be an eco-friendly additive for a variety of industrial applications.

Abstract

An increased need by the green industry for enzymes that can be exploited for eco-friendly industrial applications led us to isolate and identify a unique protease obtained from a proteolytic Bacillus megaterium-TK1 strain from a seawater source. The extracellular thermostable serine protease was processed by multiple chromatography steps. The isolated protease displayed a relative molecular weight (MW) of 33 kDa (confirmed by zymography), optimal enzyme performance at pH 8.0, and maximum enzyme performance at 70 °C with 100% substrate specificity towards casein. The proteolytic action was blocked by phenylmethylsulfonyl fluoride (PMSF), a serine hydrolase inactivator. Protease performance was augmented by several bivalent metal cations. The protease tolerance was studied under stringent conditions with different industrial dispersants and found to be stable with Surf Excel, Tide, or Rin detergents. Moreover, this protease could clean blood-stained fabrics and showed dehairing activity for cow skin with significantly reduced pollution loads. Our results suggest that this serine protease is a promising additive for various eco-friendly usages in both the detergent and leather industries.

Production and characterization of a novel thermo- and detergent stable keratinase from Bacillus sp. NKSP-7 with perceptible applications in leather processing and laundry industries

Keratinase has the ability to degrade the recalcitrant keratinous wastes that cannot be degraded by conventional proteases. The present study describes a novel hyperstable keratinolytic enzyme from Bacillus sp. NKSP-7, which has excellent efficiency of keratin-feather biodegradation, washing and dehairing. The production of extracellular keratinase was improved by 3.02-fold through optimization of various parameters. Purified keratinase (25 kDa) showed optimal activity at 65 °C and pH 7.5, and displayed stability over a range of pH (5.5-9.5) and temperature (20-60 °C) for 8 h. No conspicuous effect was perceived with various chemicals and organic solvents, however, the catalytic efficiency was enhanced in the presence of Ca²⁺, Cd²⁺, Na⁺, Mn²⁺, sodium sulfite, and β-mercaptoethanol. The enzyme was completely inhibited by phenylmethanesulfonyl fluoride (PMSF), suggesting that this keratinase belongs to serine protease family. It displayed prodigious stability and compatibility to salinity and commercial detergents. Enzyme exhibited great substrate specificity but high affinity was observed with keratin-rich substrates. Crude and purified keratinase revealed perceptible potential for destaining of blood-stained fabric (10 min), and dehairing of hide (8 h) without any damage. All these auspicious features make this enzyme a promising candidate for various industrial applications, especially in keratin-waste management, detergent formulations and leather processing.

The Practical Potential of Bacilli and Their Enzymes for Industrial Production

Bacillus spp. are an affordable source of enzymes due to their wide distribution, safety in work, ease of cultivation, and susceptibility to genetic transformations. Researchers are particularly interested in proteolytic enzymes, which constitute one of the most diverse groups of microbial proteins in terms of properties. Despite the long history of their research, this group of enzymes continue to show great potential for practical application in the biomedical industry, as well as in the agricultural industry. Thus, the unique properties of bacillary proteinases, such as stability in a wide range of temperatures and pH, high specificity, biodegradability of a wide range of substrates, and the high potential of sequenced Bacillus genomes are a powerful foundation for the development of new biotechnologies. The current review aims to discuss recent studies on various enzymes in particular, proteinases produced by bacteria of the genus Bacillus, along with their prospective practical applications. This article also presents an interpretive summary of the recent developments on the usage of probiotic Bacillus strains as potential feed additives.

Nutritional Enhancement of Chicken Feather Waste by Bacillus aerius NSMk2

Keratinous waste is the bulk by-product of various livestock industries. Slow natural degradation of keratin and less efficient chemical hydrolysis imposes challenge for the search of alternative recycling methods. Keratin degrading microbes hydrolyse keratin to soluble peptides and amino acids. Bacillus aerius NSMk2 showed great potential for hydrolysis of chicken feather waste. Bacillus aerius NSMk2 cells grown in phosphate buffer supplemented with chicken feathers showed high disulfide reductase activity and release of sulfhydryl groups. The release of proteins and amino acids were statistically optimized at varied pH (4.0-11.0), temperature (30.0-45.0 °C) and agitation (100-250 rpm), and maximum release was recorded at pH 7.5, temperature 37 °C and shaking (175 rpm). FTIR and SEM showed sulfitolysis and extensive keratinolysis of feathers resulting in complete hydrolysis of white chicken feathers after 84 h. MALDI-TOF mass spectrometry confirmed the release of low molecular weight peptides in the range of 399 to 3289.4 m/z. The present study demonstrates management of otherwise hard-to-degrade keratinous waste and simultaneous nutritional enhancement of waste chicken feathers to value-added hydrolysate that can be used in livestock feed formulations or biofertilizer in agro-industry.

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.

Challenges and Opportunities in Identifying and Characterising Keratinases for Value-Added Peptide Production

Keratins are important structural proteins produced by mammals, birds and reptiles. Keratins usually act as a protective barrier or a mechanical support. Millions of tonnes of keratin wastes and low value co-products are generated every year in the poultry, meat processing, leather and wool industries. Keratinases are proteases able to breakdown keratin providing a unique opportunity of hydrolysing keratin materials like mammalian hair, wool and feathers under mild conditions. These mild conditions ameliorate the problem of unwanted amino acid modification that usually occurs with thermochemical alternatives. Keratinase hydrolysis addresses the waste problem by producing valuable peptide mixes. Identifying keratinases is an inherent problem associated with the search for new enzymes due to the challenge of predicting protease substrate specificity. Here, we present a comprehensive review of twenty sequenced peptidases with keratinolytic activity from the serine protease and metalloprotease families. The review compares their biochemical activities and highlights the difficulties associated with the interpretation of these data. Potential applications of keratinases and keratin hydrolysates generated with these enzymes are also discussed. The review concludes with a critical discussion of the need for standardized assays and increased number of sequenced keratinases, which would allow a meaningful comparison of the biochemical traits, phylogeny and keratinase sequences. This deeper understanding would facilitate the search of the vast peptidase family sequence space for novel keratinases with industrial potential.