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

Heterologous expression and purification of keratinase from Actinomadura viridilutea DZ50: feather biodegradation and animal hide dehairing bioprocesses

The keratin-degrading bacterium Actinomadura viridilutea DZ50 secretes a keratinase (KERDZ) with potential industrial interest. Here, the kerDZ gene was extracellularly expressed in Escherichia coli BL21(DE3)pLysS using pTrc99A vector. The recombinant enzyme (rKERDZ) was purified and biochemically characterized. Results showed that the native and recombinant keratinases have similar biochemical characteristics. The conventional dehairing with lime and sodium sulfide degrades the hair to the extent that it cannot be recovered. Thus, these chemical processes become a major contributor to wastewater problem and create a lot of environmental concern. The complete dehairing was achieved with 2000 U/mL rKERDZ for 10 h at 40 °C. In fact, keratinase assisted dehairing entirely degraded chicken feather (45 mg) and removed wool/hair from rabbit, sheep, goat, or bovine' hides (1.6 kg) while preserving the collagen structure. The enzymatic process is the eco-friendly option that reduces biological (BOD) (50%) and chemical (COD) oxygen demands (60%) in leather processing. Consequently, the enzymatic hair removal process could solve the problem of post-treatments encountering the traditional leather processing. The enzymatic (rKERDZ) dehaired leather was analyzed by scanning electron microscopic (SEM) studies, which revealed similar fiber orientation and compactness compared with control sample. Those properties support that the rKERDZ enzyme-mediated process is greener to some extent than the traditional one.

A highly efficient protein degradation system in Bacillus sp. CN2: a functional-degradomics study

A novel protease-producing Bacillus sp. CN2 isolated from chicken manure composts exhibited a relatively high proteolytic specific activity. The strain CN2 degradome consisted of at least 149 proteases and homolog candidates, which were distributed into 4 aspartic, 30 cysteine, 55 metallo, 56 serine, and 4 threonine proteases. Extracellular proteolytic activity was almost completely inhibited by PMSF (phenylmethylsulfonyl fluoride) rather than o-P, E-64, or pepstatin A, suggesting that strain CN2 primarily secreted serine protease. More importantly, analysis of the extracellular proteome of strain CN2 revealed the presence of a highly efficient protein degradation system. Three serine proteases of the S8 family with different active site architectures firstly fragmented protein substrates which were then degraded to smaller peptides by a M4 metalloendopeptidase that prefers to degrade hydrophobic peptides and by a S13 carboxypeptidase. Those enzymes acted synergistically to degrade intact substrate proteins outside the cell. Furthermore, highly expressed sequence-specific intracellular aminopeptidases from multiple families (M20, M29, and M42) accurately degraded peptides into oligopeptides or amino acids, thus realizing the rapid acquisition and utilization of nitrogen sources. In this paper, a systematic study of the functional-degradome provided a new perspective for understanding the complexity of the protease hydrolysis system of Bacillus, and laid a solid foundation for further studying the precise degradation of proteins with the cooperative action of different family proteases. KEY POINTS: • Bacillus sp. CN2 has relatively high proteolytic specific activity. • Bacillus sp. CN2 harbors a highly efficient protein degradation system. • The site-specific endopeptidases were secreted extracellular, while the sequence-specific aminopeptidases played a role in the cell.

Optimization of Keratinase Production and Utilization of Bacillus pumilus for Feather Degradation

Soil samples were collected from the feather dumped area where Bacillus pumilus was isolated and used for keratinase production and keratinolytic activity. In the optimization study, optimal condition for enzyme production was observed at 144 h, pH 7, temperature 37°C. The organism was utilized for feather degradation study. The maximum degradation of 57% was obtained at 37°C, pH 7 and 6 days incubation. The size of keratinase was determined by SDS- PAGE and was observed as 52 KDa.

Microbial Keratinase: Next Generation Green Catalyst and Prospective Applications

The search for novel renewable products over synthetics hallmarked this decade and those of the recent past. Most economies that are prospecting on biodiversity for improved bio-economy favor renewable resources over synthetics for the potential opportunity they hold. However, this field is still nascent as the bulk of the available resources are non-renewable based. Microbial metabolites, emphasis on secondary metabolites, are viable alternatives; nonetheless, vast microbial resources remain under-exploited; thus, the need for a continuum in the search for new products or bio-modifying existing products for novel functions through an efficient approach. Environmental distress syndrome has been identified as a factor that influences the emergence of genetic diversity in prokaryotes. Still, the process of how the change comes about is poorly understood. The emergence of new traits may present a high prospect for the industrially viable organism. Microbial enzymes have prominence in the bio-economic space, and proteases account for about sixty percent of all enzyme market. Microbial keratinases are versatile proteases which are continuously gaining momentum in biotechnology owing to their effective bio-conversion of recalcitrant keratin-rich wastes and sustainable implementation of cleaner production. Keratinase-assisted biodegradation of keratinous materials has revitalized the prospects for the utilization of cost-effective agro-industrial wastes, as readily available substrates, for the production of high-value products including amino acids and bioactive peptides. This review presented an overview of keratin structural complexity, the potential mechanism of keratin biodegradation, and the environmental impact of keratinous wastes. Equally, it discussed microbial keratinase; vis-à-vis sources, production, and functional properties with considerable emphasis on the ecological implication of microbial producers and catalytic tendency improvement strategies. Keratinase applications and prospective high-end use, including animal hide processing, detergent formulation, cosmetics, livestock feed, and organic fertilizer production, were also articulated.

Bacillus sp. CSK2 produced thermostable alkaline keratinase using agro-wastes: keratinolytic enzyme characterization

BACKGROUND

Chicken feathers are the most abundant agro-wastes emanating from the poultry processing farms and present major concerns to environmentalists. Bioutilization of intractable feather wastes for the production of critical proteolytic enzymes is highly attractive from both ecological and biotechnological perspectives. Consequently, physicochemical conditions influencing keratinase production by Bacillus sp. CSK2 on chicken feathers formulation was optimized, and the keratinase was characterized.

RESULTS

The highest enzyme activity of 1539.09 ± 68.14 U/mL was obtained after 48 h of incubation with optimized conditions consisting of chicken feathers (7.5 g/L), maltose (2.0 g/L), initial fermentation pH (5.0), incubation temperature (30 °C), and agitation speed (200 rpm). The keratinase showed optimal catalytic efficiency at pH 8.0 and a temperature range of 60 °C - 80 °C. The keratinase thermostability was remarkable with a half-life of above 120 min at 70 °C. Keratinase catalytic efficiency was halted by ethylenediaminetetraacetic acid and 1,10-phenanthroline. However, keratinase activity was enhanced by 2-mercaptoethanol, dimethyl sulfoxide, tween-80, but was strongly inhibited by Al³⁺ and Fe³⁺. Upon treatment with laundry detergents, the following keratinase residual activities were achieved: 85.19 ± 1.33% (Sunlight), 90.33 ± 5.95% (Surf), 80.16 ± 2.99% (Omo), 99.49 ± 3.11% (Ariel), and 87.19 ± 0.26% (Maq).

CONCLUSION

The remarkable stability of the keratinase with an admixture of organic solvents or laundry detergents portends the industrial and biotechnological significance of the biocatalyst.

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.

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.

Biochemical and Molecular Characterization of a Thermostable Alkaline Metallo-Keratinase from Bacillus sp. Nnolim-K1

Keratinases are considerably gaining momentum in green technology because of their endowed robustness and multifaceted application potentials, such as keratinous agro-wastes valorization. Therefore, the production of novel keratinases from relatively nonpathogenic bacteria grown in agro-wastes formulated medium is cost-effective, and also imperative for the sustainability of thriving bioeconomy. In this study, we optimized keratinase production by Bacillus sp. Nnolim-K1 grown in chicken feather formulated medium. The produced keratinase (KerBNK1) was biochemically characterized and also, the keratinase-encoding gene (kerBNK1) was amplified and sequenced. The optimal physicochemical conditions for extracellular keratinase production determined were 0.8% (w/v) xylose, 1.0% (w/v) feather, and 3.0% (v/v) inoculum size, pH 5.0, temperature (25 °C) and agitation speed (150 rpm). The maximum keratinase activity of 1943.43 ± 0.0 U/mL was achieved after 120 h of fermentation. KerBNK1 was optimally active at pH and temperature of 8.0 and 60 °C, respectively; with remarkable pH and thermal stability. KerBNK1 activity was inhibited by ethylenediamine tetra-acetic acid and 1,10-phenanthroline, suggesting a metallo-keratinase. The amplified kerBNK1 showed a band size of 1104 bp and the nucleotide sequence was submitted to the GenBank with accession number MT268133. Bacillus sp. Nnolim-K1 and the keratinase displayed potentials that demand industrial and biotechnological exploitations.

Exoproduction and characterization of a detergent-stable alkaline keratinase from Arthrobacter sp. KFS-1

Arthrobacter sp. KFS-1 previously isolated from a dump site was used to produce keratinase in basal medium. The physico-chemical conditions were optimized to enhance the keratinase production, and biochemical properties of the enzyme were also evaluated. Arthrobacter sp. KFS-1 optimally produced keratinase in a basal medium that contained 1.0 g/L xylose, 2.5-5.0 g/L chicken feather; with initial pH, incubation temperature and agitation speed of 6.0, 30 °C and 200 rpm, respectively. Maximum keratinase activity of 1559.09 ± 29.57 U/mL was achieved at 96 h of fermentation; while optimal thiol concentration of 665.13 ± 38.73 μM was obtained at 144 h. Furthermore, the enzyme was optimally active at pH 8.0 and 60 °C. The enzyme activity was inhibited by ethylene diamine tetraacetic acid and 1,10-phenanthroline, but not affected by phenylmethylsulfonyl floride. In addition, the crude enzyme retained 55%, 63%, 80%, 81% and 90% of the original activity after respective pretreatment with some commercial detergents (Maq, Omo, Surf, Sunlight and Ariel). Moreso, the enzyme showed remarkable stability in the presence of reducing agents, surfactants, and organic solvents. Arthrobacter sp. KFS-1 significantly produced keratinase which exhibited excellent stability in presence of chemical agents and commercial laundry detergents; hence, suggesting its industrial application potentials especially in detergent formulation.

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.

Production of bioflocculant using feather waste as nitrogen source and its use in recycling of straw ash-washing wastewater with low-density and high pH property

Straw ash-washing wastewater is generated in the process of straw combustion power generation and potash fertilizer production. The suspended solid particles in straw ash-washing wastewater are hard to be settled down due to its low-density and high pH properties which inhibit the application of traditional chemical flocculants. Bioflocculant has good advantages in flocculating activity, biodegradability and adaptability of wastewater pH fluctuation. However, high production cost limited the large-scale applications of bioflocculant in wastewater treatment. In this study, the feasibility of using feather waste as cheap alternative nitrogen source of alkaliphilic Bacillus agaradhaerens C9 to produce bioflocculant was investigated. The results showed that strain C9 could simultaneously produce keratinase and bioflocculant, and thereby producing bioflocculant (named as BFF) using feather waste as cheap nitrogen source. The optimal fermentation conditions for enzymatic hydrolysis of feather waste and BFF production was 40 g/L feather wastes, 16 g/L glucose, 37 °C and pH 9.5, and the highest yield of 2.5 g/L was obtained. Moreover, BFF was used to flocculate straw ash-washing wastewater which exhibits low-density and high pH properties, and the highest flocculating rate of 93.1% was achieved when 6.0 mg/L BFF was added. This study reported for the first time that feather waste was used as inexpensive alternative nitrogen source for producing bioflocculant which could treat straw ash-washing wastewater, thereby promoting the resourceful utilization of feather waste and the reuse of straw ash-washing wastewater.

Response Surface Methodology for the Optimization of Keratinase Production in Culture Medium Containing Feathers by Bacillus sp. UPM-AAG1

Keratinase is a type of proteolytic enzyme with broad application in industry. The main objective of this work is the optimization of keratinase production from Bacillus sp. strain UPM-AAG1 using Plackett-Burman (PB) and central composite design (CCD) for parameters, such as pH, temperature, feather concentration, and inoculum size. The optimum points for temperature, pH, and inoculum and feather concentrations were 31.66 °C, 6.87, 5.01 (w/v), and 4.53 (w/v), respectively, with an optimum keratinase activity of 60.55 U/mL. The keratinase activity was further numerically optimized for commercial application. The best numerical solution recommended a pH of 5.84, temperature of 25 °C, inoculums’ size of 5.0 (v/v), feather concentration of 4.97 (w/v). Optimization resulted an activity of 56.218 U/mL with the desirability value of 0.968. Amino acid analysis profile revealed the presence of essential and non-essential amino acids. These properties make Bacillus sp. UPM-AAG1 a potential bacterium to be used locally for the production of keratinase from feather waste.

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

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

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

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

Proteolytic bacteria isolated from agro-waste dumpsites produced keratinolytic enzymes

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Proteolytic bacteria were isolated from agro-waste dumpsites.

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The isolates degraded intact feathers and produced keratinases in basal media.

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Feather degradation generated high concentration of free thiol containing groups.

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The remarkable thiol concentrations suggest keratinous waste valorisation potential of these bacteria.

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The isolates were identified through 16S rDNA sequence as Bacillus spp. and Arthrobacter sp.

Microbial bioconversion of carbonoclastic materials is an efficient tool for the exploitation and valorization of underutilized agro-industrial wastes. The agro-industrial sector accumulates tones of keratinous wastes biomass which may be valorized into high value products. Consequently, the keratinolytic potentials of some bacteria isolated from terrestrial milieu was evaluated. Soil samples were collected from dumpsites, keratinase producing bacteria were isolated. Bacterial species were identified through 16S rRNA gene sequences. The keratinase activity was assessed in relation to thiol formation, percentage feather degradation and quantitation of keratinase produced. Keratinolytic bacteria were identified as Bacillus spp. (accession numbers: MG214989 – MG214992, MG214997, MG214998, MG215000, MG215002–MG215005) and Arthrobacter sp. (accession numbers; MG215001). The degree of chicken feather degradation ranged from 61.5 ± 0.71 % to 85.0 ± 1.41 %. Similarly, the activity of keratinase, total protein and thiol group ranged from 198.18 ± 15.43–731.83 ± 14.14 U/mL; 0.09 ± 0.01–0.87 ± 0.05 mg/mL; and 0.69 ± 0.12–2.89 ± 0.11 mM respectively. Notably, Bacillus sp. Nnolim-K1 displayed the best keratinolytic potential with extracellular keratinase activity and feather degradation of 731.83 ± 14.14 U/mL and 85.0 ± 1.41 % respectively, and that is an indication of a potential relevance biotechnologically.

Biotransformation of keratin waste to amino acids and active peptides based on cell-free catalysis

BACKGROUND

Keratin is the primary constituent of the vertebrate epidermis and epidermal appendages, as well as the main waste product generated during poultry processing from feathers, hair, scales, nails, etc. Keratin is generally hard, stubborn and difficult to hydrolyze; however, it is also inexpensive and contains more than 85% protein. Currently, tens of millions of tons of keratin waste are produced each year worldwide; however, no effective methods for the recovery of keratin waste have been reported thus far, making such research urgent. Keratinase has been reported to be useful for keratin waste recovery; however, nearly all keratinases are unable to hydrolyze keratin after they are detached from living cell systems. This may be due to low keratinase activity and lack of synergistic factors.

RESULTS

Herein, the keratinase gene from Bacillus licheniformis BBE11-1 was successfully expressed in Bacillus subtilis WB600, allowing for improved activity of the recombinant keratinase KerZ1 to 45.14 KU/mL via promoter substitution and screening of the ribosome-binding sites. Further, real-time control of temperature, pH, dissolved oxygen, and feed strategy allowed the activity of KerZ1 to reach 426.60 KU/mL in a 15-L fermenter, accounting for a 3552-fold increase compared to the wild-type keratinase (120.1 U/mL). Most importantly, we proposed a method based on the synergistic action of keratinase KerZ1 and sodium sulfite, to hydrolyze feathers into amino acids. In specific, 100 g/L of feather waste can be successfully converted into 56.6% amino acids within 12 h, while supporting the production of dozens of bioactive peptides.

CONCLUSIONS

The activity of recombinant keratinase can be greatly enhanced via transcription and translational regulation in Bacillus subtilis. The synergistic action of keratinase and sulfite can rapidly degrade feather waste and produce amino acids and polypeptides.

Bacillus sp. FPF-1 Produced Keratinase with High Potential for Chicken Feather Degradation

Chicken feathers are predominantly composed of keratin; hence, valorizing the wastes becomes an imperative. In view of this, we isolated keratinase-producing bacteria and identified them through the 16S rDNA sequence. The process condition for keratinase activity was optimized, and electron micrography of the degradation timelines was determined. Keratinolytic bacteria were isolated and identified as Bacillus sp. FPF-1, Chryseobacterium sp. FPF-8, Brevibacillus sp. Nnolim-K2, Brevibacillus sp. FPF-12 and Brevibacillus sp. FSS-1; and their respective nucleotide sequences were deposited in GenBank, with the accession numbers MG214993, MG214994, MG214995, MG214996 and MG214999. The degree of feather degradation and keratinase concentration among the isolates ranged from 62.5 ± 2.12 to 86.0 ± 1.41(%) and 214.55 ± 5.14 to 440.01 ± 20.57 (U/mL), respectively. In the same vein, 0.1% (w/v) xylose, 0.5% (w/v) chicken feather, an initial fermentation pH of 5.0, fermentation temperature of 25 °C and an agitation speed of 150 rpm, respectively, served as the optimal physicochemical conditions for keratinase activity by Bacillus sp. FPF-1. The time course showed that Bacillus sp. FPF-1 yielded a keratinase concentration of 1698.18 ± 53.99(U/mL) at 120 h. The electron microscopic imaging showed completely structural dismemberment of intact chicken feather. Bacillus sp. FPF-1 holds great potential in the valorization of recalcitrant keratinous biomass from the agro sector into useful products.

Efficient keratinase expression via promoter engineering strategies for degradation of feather wastes

Keratinases are promising alternatives over ordinary proteases in several industrial applications due to their unique properties compared with their counterparts in the protease categories. However, their large-scale industrial application is limited by the low expression and poor fermentation efficiency of keratinase. Here, we demonstrate that the expression level of keratinase can be improved by constructing a more efficient enzyme expression system hereby enables the highest production titer as regarding recombinant keratinase production to date. Specially, ten promoters were evaluated and the aprE promoter exhibits a significant promotion of keratinase (kerBv) titer from 165 U/mL to 2605 U/mL in Bacillus subtilis. The batch fermentation mode resulted in a maximum keratinase activity of 7176 U/mL at 36 h in a 5-L fermenter. Furthermore, the extracellular keratinase activity attained up to 16,860 U/mL via fed-batch fermentation within 30 h. The combination of keratinase with l-cysteine brings about 66.4 % degree of degradation of feather. Our work provides a new insight into the development of efficient keratinase fermentation processes with B. subtilis cell factory.

Fusarium oxysporum and Aspergillus sp. as Keratinase Producers Using Swine Hair From Agroindustrial Residues

Technological processes mediated by microorganisms and enzymes are promising alternatives for treatment of recalcitrant residues. Keratinases hydrolyze keratin, the primary component of some wastes generated in many industrial activities. The present study was designed to evaluate strategies for obtaining keratinases produced by fungi using submerged fermentation and two residues as substrates, chicken feathers and swine hair. Two fungi isolated from feather residues showed potential for keratinase production, Fusarium oxysporum and Aspergillus sp. These were subjected to submerged fermentation using chicken feathers and swine hair prepared in three conditions (microbial concentration reduction, sterilization and hydrogen peroxide). The residual mass was quantified and tested for keratinase production. The most potent enzymatic extract was used in the precipitation technique with salts and organic solvents. The best results of enzymatic activity were obtained using F. oxysporum, on the 6thday of fermentation, obtaining 243.25 U mL^–1 using sterilized swine hair as the substrate. Aspergillus sp. showed the highest keratinolytic activity on the 9thday, 113.50 U mL^–1 using feathers as the substrate. The highest degradation percentage was 59.20% (w/w) in swine hair and the precipitation technique, with relative activities close to 50%. The results are promising for the application of residues and microorganisms in biotechnological processes of economic and environmental interest.

Two novel S1 peptidases from Amycolatopsis keratinophila subsp. keratinophila D2T degrading keratinous slaughterhouse by-products

Two proteases, named C- and T-like proteases, respectively, were purified from the culture supernatant of Amycolatopsis keratinophila subsp. keratinophila D2^T grown on a keratinous slaughterhouse by-product of pig bristles and nails as sole nitrogen and carbon source. The two proteases belong to peptidase family S1 as identified by mass spectrometric peptide mapping, have low mutual sequence identity (25.8%) and differ in substrate specificity. T-like protease showed maximum activity at 40 °C and pH 8-9, and C-like protease at 60 °C and pH 8-10. Peptides released from the keratinous by-product were identified by mass spectrometry and indicated P1 specificity for arginine and lysine of T-like and alanine, valine and isoleucine of C-like protease as also supported by the activity of the two proteases towards synthetic peptide and amino acid substrates. The specific activities of the C- and T-like proteases and proteinase K on keratin azure and azokeratin were comparable. However, C- and T-like proteases showed 5-10-fold higher keratin/casein (K/C) activity ratios than that of another S1 and two keratin-degrading S8 peptidases used for comparison. The findings support that the range of peptidase families considered to contain keratinases should be expanded to include S1 peptidases. Furthermore, the results indicated the quite thermostable C-like protease to be a promising candidate for use in industrial degradation of keratinous slaughterhouse by-products.

Progress in Microbial Degradation of Feather Waste

Feathers are a major by-product of the poultry industry. They are mainly composed of keratins which have wide applications in different fields. Due to the increasing production of feathers from poultry industries, the untreated feathers could become pollutants because of their resistance to protease degradation. Feathers are rich in amino acids, which makes them a valuable source for fertilizer and animal feeds. Numerous bacteria and fungi exhibited capabilities to degrade chicken feathers by secreting enzymes such as keratinases, and accumulated evidence shows that feather-containing wastes can be converted into value-added products. This review summarizes recent progress in microbial degradation of feathers, structures of keratinases, feather application, and microorganisms that are able to secrete keratinase. In addition, the enzymes critical for keratin degradation and their mechanism of action are discussed. We also proposed the strategy that can be utilized for feather degradation. Based on the accumulated studies, microbial degradation of feathers has great potential to convert them into various products such as biofertilizer and animal feeds.

Removal of chromium from wastewater by swine hair residues applied as a putative biofilter

Swine production chain generates residues with potential application in environmental processes. This study aimed at the use of swine hair as a potential biofilter for hexavalent chromium (Cr(VI)) removal from wastewater of tannery industry. The hair was pretreated using H₂O₂ in alkaline medium, and statistical analysis was carried out to evaluate the hair degradation, as well the Cr(VI) removal by the potential pretreated biofilter. The results showed 99% of Cr(VI) removal in 105 min of treatment in large pH range (1-10). Treated and untreated effluents were submitted to cytotoxicity study using vegetable and animal cells, demonstrating a significant reduction on toxicity to both cells. Therefore, swine hair demonstrated to be a promising residue for heavy metal removal on the perspective of an environmentally friendly technique.

Effective biodegradation of chicken feather waste by co-cultivation of keratinase producing strains

BACKGROUND

Chicken feather, a byproduct of poultry-processing industries, are considered a potential high-quality protein supplement owing to their crude protein content of more than 85%. Nonetheless, chicken feathers have been classified as waste because of the lack of effective recycling methods. In our previous studies, Bacillus licheniformis BBE11-1 and Stenotrophomonas maltophilia BBE11-1 have been shown to have feather-degrading capabilities in the qualitative phase. To efficiently recycle chicken feather waste, in this study, we investigated the characteristics of feather degradation by B. licheniformis BBE11-1 and S. maltophilia BBE11-1. In addition, in an analysis of the respective advantages of the two degradation systems, cocultivation was found to improve the efficiency of chicken feather waste degradation.

RESULTS

B. licheniformis BBE11-1 and S. maltophilia BBE11-1 were used to degrade 50 g/L chicken feather waste in batches, and the degradation rates were 35.4% and 22.8% in 96 h, respectively. The degradation rate of the coculture system reached 55.2% because of higher keratinase and protease activities. Furthermore, cocultivation was conducted in a 3 L fermenter by integrating dissolved oxygen control and a two-stage temperature control strategy. Thus, the degradation rate was greatly increased to 81.8%, and the conversion rate was 70.0% in 48 h. The hydrolysates exhibited antioxidant activity and contained large quantities of amino acids (895.89 mg/L) and soluble peptides.

CONCLUSIONS

Cocultivation of B. licheniformis BBE11-1 and S. maltophilia BBE11-1 can efficiently degrade 50 g/L chicken feather waste and produce large amounts of amino acids and antioxidant substances at a conversion rate of 70.0%.

An integrated strategy for the effective production of bristle protein hydrolysate by the keratinolytic filamentous bacterium Amycolatopsis keratiniphila D2

In a conventional microorganism-mediated biological process for degradation of keratinous waste material the production of keratin-specific proteases (i.e., keratinases) and the hydrolysis of keratin-rich residual biomass both take place during the same stage of the bioprocess and, as a consequence, occur simultaneously under suboptimal conditions. In the present study the keratinolytic actinomycete Amycolatopsis keratiniphila D2 was successfully employed to biodegrade thermally pretreated porcine bristles at high solids loading (16% w/v) via a novel cultivation methodology. Indeed, the two-stage submerged fermentation process developed in this work enabled to efficiently recover, in a single unit operation, about 73% of the protein material contained in the keratinous biowaste structure, resulting in an overall accumulation of 89.3 g·L^-1 protein-rich hydrolysate and a productivity of 427 mg crude soluble proteins per litre per hour. The obtained protein hydrolysate powder displayed a 2.2-fold increase in its in vitro pepsin digestibility (95%) with respect to the non-hydrolysed pretreated substrate (43%). In addition, the chromatogram obtained by size-exclusion chromatography analysis of the final product indicated that, among the identified fractions, those consisting of small peptides and free amino acids were the most abundantly present inside the analysed sample. Given these facts it is possible to conclude that the soluble proteins, peptides and free amino acids recovered through the newly designed two-stage bioextraction process could represent a viable alternative source of protein in animal feed formulation.

Bioconversion of Chicken Feather Meal by Aspergillus niger: Simultaneous Enzymes Production Using a Cost-Effective Feedstock Under Solid State Fermentation

This study reported for the first time the simultaneous production of hydrolytic enzymes by Aspergillus niger under solid state fermentation using chicken feather meal as substrate. The effect of some culture parameters for production of protease, lipase, phytase and keratinase enzymes was evaluated using a central composite rotatable design. The results obtained demonstrated that the independent variables initial moisture of the culture medium and incubation temperature presented as highly significant on the enzymes production. The production of protease and lipase followed a similar profile, in which the highest values of enzymatic activities were detected after 48 h of fermentation. The conduction of the fermentative process using an initial moisture of 50%, 30 °C as incubation temperature and supplementation of the feather meal with 15% wheat bran resulted in higher yields of protease (> 300 U g^-1) and lipase (> 90 U g^-1) after 48 h and satisfactory values of phytase activity (> 70 U g^-1) after 72 h. No significant effects of the independent variables on keratinase production were observed. However, under the selected conditions for the other enzymes, keratinase production reached values higher than 13 U g^-1 after 72 h fermentation. Thus, our work contributed to the proposal of an alternative process for the simultaneous production of proteases, lipases, phytases and keratinases in a single and simplified process using chicken feather meal.

Combining Pro-peptide Engineering and Multisite Saturation Mutagenesis To Improve the Catalytic Potential of Keratinase

Keratinases are becoming biotechnologically important since they have shown potential in hydrolysis of recalcitrant keratins with highly rigid and strongly cross-linked structures. However, the large-scale application of keratinases has been limited by the inefficient expression level and low enzyme activity. In this work, we employed pro-peptide engineering and saturation mutagenesis to construct excellent keratinase variants with improved activities. It turned out that amino acid substitutions at the pro-peptide cleavage site (P1) could accelerate the release of active mature enzymes, resulting in a 3-fold activity increase. Eighteen sites of the pro-peptide area were targeted for codon mutagenesis, and a multisite saturation mutagenesis library of the six potential sites was generated, achieving a significant improvement of keratinase activity from 179 to 1114 units/mL. Also, the mutants exhibited alterant catalytic properties. Finally, fermentation for keratinase production in a 15 L fermenter was carried out, and the enzyme activity reached up to over 3000 units/mL. Our results demonstrated that pro-peptide engineering played a crucial role in high expression and engineering of proteases. This study provides a universal route toward improvement of industrial enzymes that were first synthesized as precursors in the form of pre-pro-protein.

Enrichment and characterization of an environmental microbial consortium displaying efficient keratinolytic activity

Keratin refers to a group of insoluble and recalcitrant protein materials. Slaughterhouses produce large amount of keratinous byproducts, which are either disposed or poorly valorized through costly thermochemical processes for animal feed formulation. Learning from nature, keratinolytic microbial consortia stand as a cost-efficient and environmental friendly way to valorize this recalcitrant resource. Directed selection was applied to enrich soil-born microbial consortia, using sequential batch cultivations in keratin medium, while measuring enzymes activity and monitoring consortia compositions via 16S rRNA gene amplicon sequencing. A promising microbial consortium KMCG6, featuring mainly members of Bacteroidetes and Proteobacteria, was obtained. It possessed keratinolytic activity with <25% residual substrate remaining, which also displayed a high degradation reproducibility level after long-term cryopreservation. This work represents an advance in the field of α-keratin degradation with potential for practical applications.