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

The flexible linker and CotG were more effective for the spore surface display of keratinase KERQ7

Feather, horn, hoof, and other keratin waste are protein-rich but limited by natural keratinase synthesis, activity, pH, and temperature stability. It is challenging to realize its large-scale application in industries. Bacillus subtilis spores are a safe, efficient, and highly resistant immobilized carrier, which can improve target proteins' resistance. In this research, KERQ7, the keratinase gene of Bacillus tequilensis strain Q7, was fused to the Bacillus subtilis genes coding for the coat proteins CotG and CotB, respectively, and displayed on the surface of B. subtilis spores. Compared with the free KERQ7, the immobilized KERQ7 showed a greater pH tolerance and heat resistance on the spore surface. The activity of CotG-KERQ7 is 1.25 times that of CotB-KERQ7, and CotG-KERQ7 is more stable. When the flexible linker peptide L3 was used to connect CotG and KERQ7, the activity was increased to 131.2 ± 3.4%, and the residual enzyme activity was still 62.5 ± 2.2% after being kept at 60 ℃ for 4 h. These findings indicate that the flexible linker and CotG were more effective for the spore surface display of keratinase to improve stress resistance and promote its wide application in feed, tanning, washing, and other industries.

An improved, optimised and robust keratin azure assay for accurate assessment of keratinase activity

Keratin, in the form of coarse sheep wool, has been identified as an undervalued natural resource, which with the appropriate tools (e.g. a keratinase biocatalyst) can be repurposed for various textile and industrial biotechnology applications. For these purposes, we describe a novel method for identifying keratinase activity through the use of α-keratin azure (KA), an anthraquinone dyed substrate. A colourimetric method monitored the keratinase activity of Proteinase K (PK), which degrades the KA substrate and releases soluble products that are observed at 595 nm. Initially, the azure dye standard, Remazol Brilliant Blue R (RBBR), was used to calibrate the assay and allowed the kinetics of the keratinase-catalysed reaction to be determined. The assay was also used to investigate substrate pre-treatment, as well as different reaction quenching/work up conditions. Milling and washing of the KA substrate provided the best reproducibility and centrifugation was the most effective method for removing unreacted starting material. This assay was then applied to investigate the reduction of the keratin disulfide bond on keratinase-catalysed degradation. This optimised, improved and robust method will enable identification of keratinases ideally suited for application in the valorisation of the α-keratin found in natural wool fibres.

Spatiotemporal dynamics of the microbial diversity on salt-preserved goatskins assessed by culturing and 16S rRNA gene amplicon sequencing

Wet-salted skin, as a special artificial high-salt environment, is rich in protein, fat, collagen and other nutrient substrates, and is a rich resource of halotolerant and halophilic microorganisms. However, knowledge gaps regarding the microbial community structure and inter taxa associations of wet-salted skin are large. In this study, the spatiotemporal dynamics and community structure of microorganisms present on wet-salted goatskins were investigated using 16S rRNA gene amplicon sequencing and culturable technique. Alpha diversity analysis based on Sobs, Chao, Ace and Shannon indices revealed that microbial diversity on the wet-salted goatskins exhibited a trend of ‘down → up → down → flat’ with time. During preservation, genera belonging to the bacteria domain such as Acinetobacter, Weissella and Streptococcus were slowly dying out, whereas those belonging to halophilic archaea such as Natrialba and Haloterrigena were gradually flourishing. Moreover, to resist high-salt stress, microorganisms on the wet-salted goatskin gradually migrated from the outside to the inside, eventually leading to the microbial diversity inside the skin being the same as or even higher than that on the skin surface. Venn diagram analysis revealed that the strains of some genera, including Psychrobacter, Salimicrobium, Salinicola, Ornithinibacillus, Halomonas, Bacillus and Chromohalobacter, were distributed throughout the interior and exterior of the wet-salted goatskin and existed during various periods. Accordingly, 45 protease-producing halophilic or halotolerant microorganisms were isolated and screened from the wet-salted goatskin using the gradient dilution plate method. Importantly, 16S rRNA genes of some bacteria exhibited less than 99.5% similarity to valid published species, indicating that they likely are novel species and have a good potential for application.

Graphical Abstract

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.

Chicken Feather Waste Valorization Into Nutritive Protein Hydrolysate: Role of Novel Thermostable Keratinase From Bacillus pacificus RSA27

Microbial keratinases exhibit a momentous role in converting keratin biowastes into exceedingly valuable protein supplements. This study reports a novel, highly stable keratinase from Bacillus pacificus RSA27 for the production of pure peptides rich in essential amino acids from chicken feathers. Purified keratinase showed a specific activity of 38.73 U/mg, 2.58-fold purification, and molecular weight of 36 kDa. Kinetic studies using a chicken feather as substrate report K_m and V_max values of 5.69 mg/ml and 142.40 μg/ml/min, respectively, suggesting significant enzyme-substrate affinity/biocatalysis. Identification and in silico structural-functional analysis of keratinase discovered the presence of distinct amino acid residues and their positions. Besides, keratinase possesses a high-affinity calcium-binding site (Asp¹²⁸, Leu¹⁶², Asn¹⁶⁴, Ile¹⁶⁶, and Val¹⁶⁸) and a catalytic triad of Asp¹¹⁹, His¹⁵¹, and Ser³⁰⁸, known attributes of serine protease (subtilisin family). Furthermore, a scale-up to 5 L fermenter revealed complete feather hydrolysis (94.5%) within 24 h with high activity (789 U/ml) and total amino acid of 153.97 μmol/ml. Finally, cytotoxicity evaluation of protein hydrolysate resulted in negligible cytotoxic effects (1.02%) on the mammalian hepatoblastoma cell line, signifying its potential biotechnological applications.

High-expression and characterization of a novel serine protease from Ornithinibacillus caprae L9T with eco-friendly applications

In the current work, a novel thermophilic serine protease gene (P3862) from Ornithinibacillus caprae L9^T was functionally expressed in Bacillus subtilis SCK6. The monomeric enzyme of about 29 kDa was purified to homogeneity with 43.91% of recovery and 2.81-folds of purification. Characterization of the purified protease revealed the optimum activity at pH 7 and 65 °C. The protease exhibited excellent activity and stability in the presence of Na⁺, Mg²⁺, Ca²⁺, ethanediol, n-hexane, Tween-20, Tween-80 and Triton X-100. P3862 displayed favorable caseinolytic activity, moderate keratinolytic activity but no collagenolytic activity. Besides, the homology model of P3862 possessed a globular configuration and characteristic of α/β hydrolase fold, and displayed stable interactions with casein, glycoprotein and keratin rather than collagen. Moreover, the crude enzyme could completely dehair goatskin within 6 h, resulting in decrease in BOD₅, COD and TSS loads by 72.86, 74.07, and 73.79%, respectively, as compared with Na₂S treatment. Biocatalytic applications revealed that it could effectively remove egg-stains from fabrics at 37 °C for 30 min with low supplementation (300 U/mL), and was able to degrade the feathers of duck and chicken. Overall, these outstanding properties make P3862 valuable in the development of environmentally friendly biotechnologies .

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.

Exoproduction and Biochemical Characterization of a Novel Serine Protease from Ornithinibacillus caprae L9T with Hide-Dehairing Activity

This study is the first report on production and characterization of the enzyme from an Ornithinibacillus species. A 4.2-fold increase in the extracellular protease (called L9^T) production from Ornithinibacillus caprae L9^T was achieved through the one-factor-at-a-time approach and response surface methodological optimization. L9^T protease exhibited a unique protein band with a mass of 25.9 kDa upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. This novel protease was active over a range of pH (4-13), temperatures (30-80°C) and salt concentrations (0-220 g/l), with the maximal activity observed at pH 7, 70°C and 20 g/l NaCl. Proteolytic activity was upgraded in the presence of Ag⁺, Ca²⁺ and Sr²⁺, but was totally suppressed by 5 mM phenylmethylsulfonyl fluoride, which suggests that this enzyme belongs to the serine protease family. L9^T protease was resistant to certain common organic solvents and surfactants; particularly, 5 mM Tween 20 and Tween 80 improved the activity by 63 and 15%, respectively. More importantly, L9^T protease was found to be effective in dehairing of goatskins, cowhides and rabbit-skins without damaging the collagen fibers. These properties confirm the feasibility of L9^T protease in industrial applications, especially in leather processing.

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.

Optimization of fermentation conditions for production of neutral metalloprotease by Bacillus subtilis SCK6 and its application in goatskin-dehairing

In this study, a high protease-producing strain was screened by spread plate method and identified by molecular biology and morphological identification. It was identified as Bacillus sp. LCB14. A neutral protease gene was cloned and heterologous expressed by B. subtilis SCK6. Then, the recombinant protease was used to dehair the goat skins. The fermentation conditions of neutral protease production by B. subtilis SCK6 were optimized. The single factor experiments, Plackett-Burma experiment, and response surface method were conducted to determine fermentation medium and culture conditions. The optimized medium contained corn meal 49 g/L, soluble starch 28 g/L, soybean meal 17 g/L, corn steep liquor powder 8 g/L, yeast extract 10 g/L, Na₂HPO₄ 2.3 g/L, KH₂PO₄ 1.9 g/L, MgSO₄ 0.5 g/L, MnCl₂ 0.1 g/L and ZnSO₄ 0.05 g/L. The optimized culture conditions were 35 °C and pH 7.0. Under the optimum conditions, the recombinant strain reached 33467.28 U/mL after 72 hr ferment. Moreover, by fed batch in 30 L fermenters, neutral protease production reached 39,440.78 U/mL and shortened fermentation time from 72 hr to 46 hr. Finally, the crude enzyme was utilized to replace sodium sulfide for dehairing of goatskins. The enzymatic dehaired pelts were white, smooth, and soft; the grain side of enzymatic dehaired pelts were clear; there was no obvious damage to the grain side of enzymatic dehaired pelts by visual observation and tactile test. Furthermore, there were no hair roots, hair follicles and other glands in enzymatic dehaired belts, and the collagen fibers of enzymatic dehaired belt were dispersed well by histological analysis.

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.

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.

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.

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.

Citrobacter diversus-derived keratinases and their potential application as detergent-compatible cloth-cleaning agents

Currently, poultry farming is one of the sectors that have a significant impact on the global economy. In recent years, there has been an increase in the production of broilers, inflicting this segment of the industry to generate tons of keratin due to huge disposal of chicken feathers. This points to the need to degrade these chicken feathers, as they have emerged as a major threat to the environment. Thus, in this study we aimed to identify keratinases that are produced by the bacterium Citrobacter diversus and further investigate the biochemical characteristics of these keratin-degrading enzymes. In a submerged medium, the bacterium was capable of degrading chicken feathers almost completely after 36 h of fermentation. We found a maximum caseinolytic activity at pH 9-10.5 and 50-55 °C, and keratinolytic activity at pH 8.5-9.5 and 50 °C. Thus, given its stability at higher temperatures, upon incubation of this enzyme extract for 1 h at 50 °C, it showed approximately 50% of the keratinolytic and 100% of the caseinolytic activity. Further, under pH stability for 48 h at 4 °C, the enzyme extract maintained greater residual activity in the pH range 6-8. Caseinolytic activity was inhibited by EDTA and PMSF, whereas the keratinolytic activity was inhibited only by EDTA. Additionally, due to its alkaline activity and detergent compatibility, this enzyme extract could improve washing performance when added to a commercial detergent formulation. Using application tests, we could demonstrate a potential use of this bacterial enzyme extract as an additive in detergents to remove egg stains from cloth.

Efficient Keratinolysis of Poultry Feather Waste by the Halotolerant Keratinase from Salicola Marasensis

Sustainable development in the bio-treatment of large-scale biomass bulks requires high performance enzymes adapted to extreme conditions. An extracellular keratinolytic extract was obtained from the culture broth of a halotolerant strain of Salicola marasensis. Keratin hydrolyzing activity of the concentrated enzyme extract was observed on a 100 mg of pretreated feather waste. The concentrated enzyme was able to hydrolyze the poultry feathers by 25% after 12 h incubation. The bio-waste material was optimally hydrolyzed at pH 9 and temperature of 40 °C. Among reductants, 1,4-dithiothreitol, L-cysteine, 2-mercaptoethanol, glutathione, and sodium sulfate showed the most remarkable effect on the bio-waste keratinolysis, while the tested surfactants and urea had no significant effect on the keratinolytic activity. Hexane and hexadecane indicated strong effect on keratinase activity and bio-treatment in the presence of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) as a hydrophobic ionic liquid resulted in a maximal of 80% extraction yield of soluble proteins from feathers. Considering the stability of the extracellular keratinolytic content in [BMIM][PF₆], the observed keratinase activity was noteworthy suggesting that the secreted enzyme may contribute to the bioconversion of feather wastes.

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.

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.

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.

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%.

Chitin extraction from shrimp waste by liquid fermentation using an alkaline protease-producing strain, Brevibacillus parabrevis

In this study, an extracellular protease, but no chitinolytic enzyme-producing strain, Brevibacillus parabrevis TKU046, has been isolated and analyzed for the deproteinization testing of shrimp waste by liquid fermentation. Deproteinization assays of shrimp waste with this microbe showed 95% protein removal after 4 days fermentation. The efficiency of chitin extraction by B. parabrevis TKU046 on wastes of three shrimp species were also investigated in which the highest deproteinization was found on cooked tiger shrimp shell. Infrared spectra (IR) of the obtained chitin displayed characteristic profiles for chitin. The culture supernatant released after fermentation greatly exhibited growth enhancing effect on Lactobacillus rhamnosus. In addition, B. parabrevis TKU046 protease was isolated and determined the characteristics. The molecular mass of B. parabrevis TKU046 protease was determined as 32 kDa and 34 kDa, respectively, by SDS-PAGE and HPLC. Overall, the findings provide strong support for the potential candidacy of this enzyme as an effective and eco-friendly alternative to the conventional chemicals used for the deproteinization of shrimp heads in the chitin processing industry, as well as the production of prebiotics to be used in the nutraceutical industry.

Microbial Keratinases: Enzymes with Promising Biotechnological Applications

Keratin is a complex and structurally stable protein found in human and animal hard tissues, such as feathers, wool, hair, hoof and nails. Some of these, like feathers and wool, represent one of the main sources of protein-rich waste with significant potential to be transformed into value-added products such as feed, fertilizers or bioenergy. A major limitation impeding valorization of keratinous substrates is their recalcitrant structure and resistance to hydrolysis by common proteases. However, specialized keratinolytic enzymes produced by some microorganisms can efficiently degrade these substrates. Keratinases have already found a purpose in pharmaceutical, textile and leather industries. However, their wider implementation in other processes, such as cost-effective (pre)treatment of poultry waste, still requires optimization of production and performance of the available enzymes. Here we present a comprehensive review covering molecular properties and characteristics of keratinases, their classification, traditional and novel approaches in discovery of novel enzymes, production, characterization, improvement and biotechnological applications.