Purification and Characterization of a Keratinase from a Feather-Degrading Fungus, Aspergillus flavus Strain K-03

Structural and enzymatic characterization of a novel metallo-serine keratinase KerJY-23

KerJY-23 was a novel keratinase from feather-degrading Ectobacillus sp. JY-23, but its enzymatic characterization and structure are still unclear. In this study, the KerJY-23 was obtained by heterologous expression in Escherichia coli BL21(DE3), and enzymatic properties indicated that KerJY-23 was optimal at 60 °C and pH 9.0 and could be promoted by divalent metal ions or reducing agents. Furthermore, KerJY-23 had a broad substrate specificity towards casein, soluble keratin, and expanded feather powder, but its in vitro degradation against chicken feathers required an additional reducing agent. Homology modeling indicated that KerJY-23 contained a highly conserved zinc-binding HELTH motif and a His-Asp-Ser catalytic triad that belonged to the typical characteristics of M4-family metallo-keratinase and serine-keratinase, respectively. Molecular docking revealed that KerJY-23 achieved a reinforced binding on feather keratin via abundant hydrogen bonding interactions. This work not only deepened understanding of the novel and interesting metallo-serine keratinase KerJY-23, but also provided a theoretical basis for realizing the efficient use of waste feather keratin.

Isolation, identification, and molecular characterization of potential keratinolytic fungus sp. from Southern Assam: relevance to poultry wastes and its biological management

Feather waste is a highly prevalent form of keratinous waste that is generated by the poultry industry. The global daily production of feather waste has been shown to approach 5 million tons, typically being disposed of through methods such as dumping, landfilling, or incineration which contribute significantly to environmental pollutions. The proper management of these keratinous wastes is crucial to avoid environmental contamination. The study was carried out to isolate the keratinolytic fungi from the poultry disposal sites of different region of North-East India to evaluate its potential in bioremediation of the feathers wastes. Out of 12 fungal strains isolated from the sites, the fungus showing the highest zone of hydrolysis on both the skim milk and keratin agar medium was selected for the study and the molecular identification of the isolate was performed through DNA sequence analysis by amplifying the internal transcribed spacer (ITS) region. The sequence results showed higher similarity (above 95%) with Aspergillus spp. and was named Aspergillus sp. Iro-1. The strain was further analyzed for its feather degrading potential which was performed in submerged conditions under optimized conditions. The study showed that the strain could effectively degrade the feathers validated through weight loss method, and the structural deformations in the feathers were visualized through scanning electron microscopy (SEM). Aspergillus sp. Iro-1 was obtained from the southern region of Assam. It would be of great importance as the implementation of this sp. can help in the bioremediation of feathers wastes in this region. This is the first study of identification of feather degrading fungus from southern part of Assam (Barak).

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.

Keratinolytic Properties of Aspergillus clavatus Promising for Biodegradation

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

One-Pot Process: Microwave-Assisted Keratin Extraction and Direct Electrospinning to Obtain Keratin-Based Bioplastic

Poultry feathers are among the most abundant and polluting keratin-rich waste biomasses. In this work, we developed a one-pot microwave-assisted process for eco-friendly keratin extraction from poultry feathers followed by a direct electrospinning (ES) of the raw extract, without further purification, to obtain keratin-based bioplastics. This microwave-assisted keratin extraction (MAE) was conducted in acetic acid 70% v/v. The effects of extraction time, solvent/feathers ratio, and heating mode (MAE vs. conventional heating) on the extraction yield were investigated. The highest keratin yield (26 ± 1% w/w with respect to initial feathers) was obtained after 5 h of MAE. Waste-derived keratin were blended with gelatin to fabricate keratin-based biodegradable and biocompatible bioplastics via ES, using 3-(Glycidyloxypropyl)trimethoxysilane (GPTMS) as a cross-linking agent. A full characterization of their thermal, mechanical, and barrier properties was performed by differential scanning calorimetry, thermogravimetric analysis, uniaxial tensile tests, and water permeability measurements. Their morphology and protein structure were investigated using scanning electron microscopy and attenuated total reflection-infrared spectroscopy. All these characterizations highlighted that the properties of the keratin-based bioplastics can be modulated by changing keratin and GPTMS concentrations. These bioplastics could be applied in areas such as bio-packaging and filtration/purification membranes.

Keratinases Produced by Aspergillus stelliformis, Aspergillus sydowii, and Fusarium brachygibbosum Isolated from Human Hair: Yield and Activity

Twenty fungal strains belonging to 17 species and isolated from male scalp hair were tested for their capacity to hydrolyze keratinous material from chicken feather. The identification of the three most efficient species was confirmed by sequencing of the internal transcribed spacer (ITS) region of rDNA. Activities of fungal keratinases produced by Aspergillus stelliformis (strain AUMC 10920), A. sydowii (AUMC 10935), and Fusarium brachygibbosum (AUMC 10937) were 113, 120, and 130 IU mg⁻¹ enzymes, respectively. The most favorable conditions were at pH 8.0 and 50 °C. Keratinase activity was markedly inhibited by EDTA and metal ions Ca⁺², Co⁺², Ni⁺², Cu⁺², Fe⁺², Mg⁺², and Zn⁺², with differences between the fungal species. To the best of our knowledge, this is the first study on the activity of keratinase produced by A. stelliformis, A. sydowii, and F. brachygibbosum. F. brachygibbosum keratinase was the most active, but the species is not recommended because of its known phytopathogenicty. Aspergillus sydowii has many known biotechnological solutions and here we add another application of the species, as producer of keratinases. We introduce A. stelliformis as new producer of active fungal keratinases for biotechnological solutions, such as in the management of keratinous waste in poultry industry.

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.

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.

Onychomycosis Unresponsive to Antifungals: Etiology and Treatment with a New Direct Technique

Aims and Objectives:

The aim of this study was to identify the fungal agents causing onychomycosis that were unresponsive to antifungal treatment and to treat these cases by placing under-nail cushions with a mild keratolytic to clear the fungus-invaded tissue.

Materials and Methods:

Fungal agents were identified by the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) technique.

Results:

Nine patients had Aspergillus spp. (7 Aspergillus niger, 2 Aspergillus flavus); four had Candida species and one had Trichophyton rubrum. All patients were free of infection at the end of treatment.

Conclusion:

As per the results, we may state that onychomycosis that is unresponsive to treatment in immunocompetent patients seems to be mostly associated with molds. Direct application of a mild keratolytic to the fungus-invaded part, e.g., the nail plate and/or nail bed and removal of fungal elements may provide a successful treatment outcome.

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.

Purification and characterization of the thermostable protease produced by Serratia grimesii isolated from channel catfish

BACKGROUND

Microbial spoilage of fishery products accounts for significant financial losses, yearly on a global scale. Psychrotrophic spoilage bacteria often secrete extracellular enzymes to break down surrounding fish tissue, rendering the product unsuitable for human consumption. For a better understanding of bacterial spoilage due to enzymatic digestion of fish products, proteases in Serratia grimesii isolated from North American catfish fillets (Ictalurus punctatus) were investigated.

RESULTS

Mass spectrometric evidence demonstrated that S. grimesii secretes two distinct extracellular proteases and one lipase. Protease secretion displayed broad thermostability in the 30-90 °C range. The major protease-secretion (O-1) was most active under alkaline conditions and utilized manganese as a co-factor. Organic solvents significantly disrupted the efficacy of S. grimesii extracellular enzymes and, in a series of bactericidal detergents, protease activity was highest when treated with Triton X-100. Ethylenediaminetetraacetic acid (EDTA) and phenylmethylsulfonyl fluoride (PMSF) significantly inhibited the enzyme activity, while protease was moderately stable under freeze-thaw and refrigerated storage.

CONCLUSION

The influence of fish spoilage-related enzymes, depending on various factors, is discussed in this paper. This study will provide new insight into enzymatic spoilage and its control, which can be exploited to enhance food safety and the shelf-life of fishery products worldwide. © 2018 Society of Chemical Industry.

Survivability of highly pathogenic avian influenza virus (H5N1) in naturally preened duck feathers at different temperatures

Ducks are the "Trojan Horses" for Asian H5N1 avian influenza viruses (AIV) and attain carrier status without displaying overt infection. These birds help in the spread of the virus among the poultry and human population through direct or indirect contact. Preen oil is the secretion of preen gland of water birds such as ducks. In a process called preening, the water birds spread preen oil across their feather and body. Preen oil has been known to play a significant role in the accumulation of various pathogens including Highly Pathogenic Avian Influenza (HPAI) from water onto feathers. However, the studies are scarce on the role of preen oil in the survivability of HPAIV. We conducted a simulative study to analyse the effect of preen oil on the survivability of the HPAI virus (H5N1) on duck feathers. Duck feather samples along with relevant controls were spiked with the H5N1 virus at two different initial concentrations (10⁴ EID₅₀ and 10⁶ EID₅₀ ), stored at 37°C, 25°C and 10°C temperatures and tested at regular intervals for percent infectivity by egg culture method and qRT-PCR. The infectivity and viral load were significantly higher in naturally preened duck feathers in comparison to the three preen oil deficit controls at both low and high initial concentrations of virus (10⁴ EID₅₀ and 10⁶ EID₅₀ ). Maximum persistence was seen at 10°C in naturally preened duck feathers spiked with 10⁶ EID₅₀ concentration of viruses. It was also seen that depletion of preen oil from duck feathers reduced the persistence of the virus. These results demonstrate that preen oil plays a significant role in survivability and protection of HPAIV on duck feathers. This study herein will present new avenues in understanding one of the epidemiological niches of HPAIV.

Secretory expression and purification of Bacillus licheniformis keratinase in insect cells

The keratinase (kerA) gene from Bacillus licheniformis PWD-1 was expressed and purified in insect cells. First, the sequence encoding Ker-His-Flag was designed based on the amino acid sequence of the protein and peptide and codon optimization in order to ensure the high expression in insect cells. In the next step, the synthetic DNA was inserted into the pUC57 vector and then sub-cloned in the pFastBac™-1 donor vector by BamHI/HindIII restriction sites. The constructed vector was transformed to E. coli DH10Bac™ cell to generate recombinant bacmid carrying Ker-His-Flag. Recombinant viruses were produced by infecting insect Spodoptera frugiperda (Sf9) cells with bacmid DNA and used for proteins production. Target proteins were purified from the cell supernatants by Ni²⁺-NTA affinity chromatography and evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and western blot. The purified product contained two peptides with molecular weights of 38 kDa and 30 kDa and had an optimal pH and temperature at 8.0 and 45°C for keratinolytic activity, respectively. The final product had a specific activity of about 635 U/mg. In summary, we have demonstrated that the open reading frame containing recombinant Ker-His-Flag was expressed and secreted by leader peptide of mellittin from Apis mellitera in insect cells and affinity purification through 8His-Flag tag. It presents an alternative technology for producing keratinases. To our knowledge, it was the first report on the expression of functional keratinase from Bacillus licheniformis in insect cells system.

The feather-degrading bacterial community in two soils as revealed by a specific primer targeting serine-type keratinolytic proteases

Feather waste represents a huge resource of protein, but is underutilized due to its recalcitrant nature. Feather-degrading bacteria can biologically degrade feathers and have great potential for industries. In this study, we first designed a primer set (BC) suitable for exploring the diversity of the keratinolytic bacterial community with denatured gradient gel electrophoresis (DGGE). With the BC primer set, the difference in the keratinolytic bacterial community between a feather-dumping (FD) soil and a non feather-dumping (NFD) soil and the influence of feather addition (enrichment culture) on the keratinolytic bacterial community were investigated. DGGE and sequencing showed that keratinolytic bacteria in these soils belong to 2 phyla (Actinobacteria and Proteobacteria) and 9 genera (Micromonospora, Verrucosispora, Actinopolymorpha, Knoellia, Hyalangium, Stigmatella, Archangium, Cystobacter, and Luteimonas). Feather addition decreased the species richness of the keratinolytic bacteria in FD soil, but greatly increased the diversity, species richness and abundance in NFD soil. Moreover, feather addition to NFD soil induced some keratinolytic bacteria that were absent in all of the other soils. Collectively, these data indicate that keratinolytic bacteria are diverse in both FD and NFD soil, and some novel keratinolytic bacteria taxa might be revealed by using the BC primer set.

From feathers to syngas - technologies and devices

The poultry waste produced by industrial slaughterhouses typically contains not only feathers, but also a mixture of animal entrails, nails, blood, beaks and whole carcasses. Economical utilisation of this mixture, varying strongly in composition and moisture content, is, in general, difficult. We demonstrate that this awkward material can be successfully used for gasification in a simple, fixed-bed gasifier. The method of gasification, which we developed, enables control of the gasification process and ensures its stability in the operational regime of a working poultry processing plant. The installation, which has been working in Poland for 2 years, utilises 2 tons of feathers per hour and produces syngas of stable composition and fairly high quality. The syngas is burnt in the combustion chamber adjacent to the gasifier. Heat is recuperated in a boiler producing 3.5 tons per hour of technological steam continuously used for the operation of the slaughterhouse. The whole process complies with the stringent emission standards. In the paper we present the end-use device for feather utilisation and describe the underlying gasification and syngas combustion processes. Key elements of the whole installation are briefly discussed. The environmental impacts of the installation are summarized.