Biodegradation of hard keratins by two bacillus strains

Insights into the keratin efficient degradation mechanism mediated by Bacillus sp. CN2 based on integrating functional degradomics

BACKGROUND

Keratin, the main component of chicken feather, is the third most abundant material after cellulose and chitin. Keratin can be converted into high-value compounds and is considered a potential high-quality protein supplement; However, its recalcitrance makes its breakdown a challenge, and the mechanisms of action of keratinolytic proteases-mediated keratinous substrates degradation are not yet fully elucidated. Bacillus sp. CN2, having many protease-coding genes, is a dominant species in keratin-rich materials environments. To explore the degradation patterns of feather keratin, in this study, we investigated the characteristics of feather degradation by strain CN2 based on the functional-degradomics technology.

RESULTS

Bacillus sp. CN2 showed strong feather keratin degradation activities, which could degrade native feathers efficiently resulting in 86.70% weight loss in 24 h, along with the production of 195.05 ± 6.65 U/mL keratinases at 48 h, and the release of 0.40 mg/mL soluble proteins at 60 h. The extracellular protease consortium had wide substrate specificity and exhibited excellent biodegradability toward soluble and insoluble proteins. Importantly, analysis of the extracellular proteome revealed the presence of a highly-efficient keratin degradation system. Firstly, T3 γ-glutamyltransferase provides a reductive force to break the dense disulfide bond structure of keratin. Then S8B serine endopeptidases first hydrolyze keratin to expose more cleavage sites. Finally, keratin is degraded into small peptides under the synergistic action of proteases such as M4, S8C, and S8A. Consistent with this, high-performance liquid chromatography (HPLC) and amino acid analysis showed that the feather keratin hydrolysate contained a large number of soluble peptides and essential amino acids.

CONCLUSIONS

The specific expression of γ-glutamyltransferase and co-secretion of endopeptidase and exopeptidase by the Bacillus sp. CN2 play an important role in feather keratin degradation. This insight increases our understanding of the keratinous substrate degradation and may inspire the design of the optimal enzyme cocktails for more efficient exploration of protein resources in industrial applications.

Feather-Degrading Bacillus cereus HD1: Genomic Analysis and Its Optimization for Keratinase Production and Feather Degradation

Keratinase is an important enzyme that is used to degrade feather wastes produced by poultry industries and slaughterhouses that accumulate rapidly over time. The search for keratinase-producing microorganisms is important to potentially substitute physicochemical treatments of feather waste. In this study, the genome of Bacillus cereus HD1 and its keratinolytic prowess was investigated. The whole-genome shotgun size is 5,668,864 bp consisting of 6083 genes, 69 tRNAs, and 10 rRNAs. The genomic analyses revealed 15 potential keratinase genes and other enzymes that might assist keratin degradation, such as disulfide reductase and cysteine dioxygenase. The optimal conditions for feather degradation and keratinase production by B. cereus HD1 such as incubation time, pH, temperature, yeast extract, and glycerol concentrations were determined to be 5 days, pH 8, 37 °C, 0.05% (w/v), and 0.1% (v/v), respectively. Under optimized conditions, B. cereus HD1 exhibited feather degradation of 65%, with bacterial growth and maximum keratinase activity of 1.3 × 10¹¹ CFU/mL and 41 U/mL, respectively, after 5 days of incubation in a feather basal medium. The findings obtained from this study may facilitate further research into utilizing B. cereus HD1 as a prominent keratinolytic enzymes production host and warrant potential biotechnological applications.

A Newly Isolated Strain Lysobacter brunescens YQ20 and Its Performance on Wool Waste Biodegradation

Wool keratin is difficult to degrade as comparing to feathers because of its tough secondary structure. In order to develop an approach for high-value utilization of wool fiber waste by keratinolytic microorganisms, which is produced from shearing, weaving, and industrial processing of wool, screening of wool-degrading bacterium with high degradation efficiency were performed in this study. To this end, Lysobacter brunescens YQ20 was identified and characterized. The optimized conditions for wool degradation were pH 9.0 and 37°C with 20% liquid volume of Erlenmeyer flask. After fermentation, 15 essential amino acids were detected when wool fiber waste was fermented. The total amino acids produced from 1% wool per hour were 13.7 mg/L. The concentration was 8.6-fold higher than that produced by the strain Stenotrophomonas maltophilia BBE11-1, which had previously been reported to have the highest wool-degrading capacity. Our study reports the first Lysobacter strain that exhibits efficient wool degradation and yields higher concentrations of amino acids than previously reported strains. Whole-genome sequencing indicated that there were 18 keratinase-like genes in the genome of YQ20, which exhibited a long evolutionary distance from those of Bacillus. Therefore, L. brunescens YQ20 may have applications in the environmentally friendly management of wool waste as fertilizer in agriculture.

Prediction of Bioactive Peptides From Chicken Feather and Pig Hair Keratins Using In Silico Analysis Based on Fragmentomic Approach

BACKGROUND

Keratin is among the most abundant structural proteins of animal origin, however it remains broadly underutilized. <P> Objective: Bioinformatic investigation was performed to evaluate selected keratins originating from mass-produced waste products, i.e., chicken feathers and pig hair, as potential sources of bioactive peptides. <P> Methods: Pepsin, trypsin, chymotrypsin, papain, and subtilisin were used for in silico keratinolysis with the use of "Enzyme(s) action" and fragmentomic analysis of theoretical products was performed using "Profiles of potential biological activity" in BIOPEP-UWM database of bioactive peptides. Bioactivity probability calculation and toxicity prediction of the peptides obtained were estimated using PeptideRanker and ToxinPred tools, respectively. <P> Results: Our results showed that the keratins are a potential source of a variety of biopeptides, including dipeptidyl peptidase IV, angiotensin converting enzyme, prolyl endopeptidase inhibitory and antioxidative. Papain and subtilisin were found to be the most appropriate enzymes for keratin hydrolysis. This study presents possible structures of keratin-derived bioactive peptides that have not been previously described. <P> Conclusion: Our data suggest additional in vitro and in vivo studies to verify theoretical predictions and further investigate the possibility of using keratin-rich waste as a source of peptide nutraceuticals.

Inactivation of indicator microorganisms and biological hazards by standard and/or alternative processing methods in Category 2 and 3 animal by-products and derived products to be used as organic fertilisers and/or soil improvers

The European Commission requested EFSA to assess if different thermal processes achieve a 5 log10 reduction in Enterococcus faecalis or Salmonella Senftenberg (775W) and (if relevant) a 3 log10 reduction in thermoresistant viruses (e.g. Parvovirus) as well as if different chemical processes achieve a 3 log10 reduction of eggs of Ascaris sp., in eight groups of Category 2 and 3 derived products and animal by-products (ABP). These included (1) ash derived from incineration, co-incineration and combustion; (2) glycerine derived from the production of biodiesel and renewable fuels; (3) other materials derived from the production of biodiesel and renewable fuels; (4) hides and skins; (5) wool and hair; (6) feathers and down; (7) pig bristles; and (8) horns, horn products, hooves and hoof products. Data on the presence of viral hazards and on thermal and chemical inactivation of the targeted indicator microorganisms and biological hazards under relevant processing conditions were extracted via extensive literature searches. The evidence was assessed via expert knowledge elicitation. The certainty that the required log10 reductions in the most resistant indicator microorganisms or biological hazards will be achieved for each of the eight groups of materials mentioned above by the thermal and/or chemical processes was (1) 99-100% for the two processes assessed; (2) 98-100% in Category 2 ABP, at least 90-99% in Category 3 ABP; (3) 90-99% in Category 2 ABP; at least 66-90% in Category 3 ABP; (4) 10-66% and 33-66%; (5) 1-33% and 10-50%; (6) 66-90%; (7) 33-66% and 50-95%; (8) 66-95%, respectively. Data generation on the occurrence and reduction of biological hazards by thermal and/or chemical methods in these materials and on the characterisation of the usage pathways of ABP as organic fertilisers/soil improvers is recommended.

Structure, Application, and Biochemistry of Microbial Keratinases

Keratinases belong to a class of proteases that are able to degrade keratins into amino acids. Microbial keratinases play important roles in turning keratin-containing wastes into value-added products by participating in the degradation of keratin. Keratin is found in human and animal hard tissues, and its complicated structures make it resistant to degradation by common proteases. Although breaking disulfide bonds are involved in keratin degradation, keratinase is responsible for the cleavage of peptides, making it attractive in pharmaceutical and feather industries. Keratinase can serve as an important tool to convert keratin-rich wastes such as feathers from poultry industry into diverse products applicable to many fields. Despite of some progress made in isolating keratinase-producing microorganisms, structural studies of keratinases, and biochemical characterization of these enzymes, effort is still required to expand the biotechnological application of keratinase in diverse fields by identifying more keratinases, understanding the mechanism of action and constructing more active enzymes through molecular biology and protein engineering. Herein, this review covers structures, applications, biochemistry of microbial keratinases, and strategies to improve its efficiency in keratin degradation.

Molecular strategies to increase keratinase production in heterologous expression systems for industrial applications

Keratinase is an important enzyme that can degrade recalcitrant keratinous wastes to form beneficial recyclable keratin hydrolysates. Keratinase is not only important as an alternative to reduce environmental pollution caused by chemical treatments of keratinous wastes, but it also has industrial significance. Currently, the bioproduction of keratinase from native keratinolytic host is considered low, and this hampers large-scale usage of the enzyme. Straightforward approaches of cloning and expression of recombinant keratinases from native keratinolytic host are employed to elevate the amount of keratinase produced. However, this is still insufficient to compensate for the lack of its large-scale production to meet the industrial demands. Hence, this review aimed to highlight the various sources of keratinase and the strategies to increase its production in native keratinolytic hosts. Molecular strategies to increase the production of recombinant keratinase such as plasmid selection, promoter engineering, chromosomal integration, signal peptide and propeptide engineering, codon optimization, and glycoengineering were also described. These mentioned strategies have been utilized in heterologous expression hosts, namely, Escherichia coli, Bacillus sp., and Pichia pastoris, as they are most widely used for the heterologous propagations of keratinases to further intensify the production of recombinant keratinases adapted to better suit the large-scale demand for them. KEY POINTS: • Molecular strategies to enhance keratinase production in heterologous hosts. • Construction of a prominent keratinolytic host from a native strain. • Patent analysis of keratinase production shows rapid high interest in molecular field.

Enhanced nail delivery of voriconazole-loaded nanomicelles by thioglycolic acid pretreatment: A study of protein dynamics and disulfide bond rupture

This work aimed to select an effective penetration enhancer (PE) for nail pretreatment, develop voriconazole (VOR)-loaded nanomicelles, and evaluate their ability to deliver VOR to the nail. A complete analysis of nail protein dynamics, bond rupture, and microstructure was performed. Alternative methods as electron paramagnetic resonance (EPR) and the Ellman's reagent (DTNB) assay were also evaluated. Nanomicelles were produced and characterized. The PE hydrated the hooves, following the order: urea ≈ cysteine ≈ glycolic acid < thioglycolic acid (TGA) < NaOH. SEM images and methylene blue assay showed enlarged pores and roughness of porcine hooves after incubation with NaOH and TGA. EPR was demonstrated to be the most sensitive technique. DTNB assay quantified higher thiol groups for samples treated with TGA (p < 0.05). A stratigraphic analysis with Raman spectroscopy demonstrated that hooves treated with TGA presented a higher SH/SS ratio at the edges, affecting protein secondary structure. In vitro permeation studies demonstrated significant VOR permeation (29.44 ± 6.13 µg/cm²), 10-fold higher than previous studies with lipid nanoparticles. After TGA pretreatment, VOR permeation was further enhanced (3-fold). TGA pretreatment followed by VOR-loaded nanomicelles demonstrates a promising approach for onychomycosis treatment. The novel methods for protein analysis were straightforward and helpful.

Simultaneous production of proteases and antioxidant compounds from agro-industrial by-products

The use of processes for simultaneous production of bioproducts as enzymes and bioactive compounds is an interesting alternative to reduce environmental impacts. Thus, the aim of this study was to produce simultaneously, using the biorefinery concept, both proteases and bioactive compounds with antioxidant activity from Bacillus sp. P45 cultivation by using different by-products. The integrated process developed in this study enabled to obtain enzymes with proteolytic and keratinolytic properties in a process with alternate substrates from agro-industrial by-products (feather meal, residual feather meal and biomass), thus, creating an interesting alternative to managing them. The residual biomass provided the highest protease activity (1306.6U/mL) and the reused feather meal reached the highest keratinolytic activity (89U/mL), both at 32h of cultivation. Moreover, hydrolysates produced in cultivation using feather meal and residual biomass had high antioxidant activity, they have great potential as natural antioxidants.

Microbial decomposition of keratin in nature-a new hypothesis of industrial relevance

Discovery of keratin-degrading enzymes from fungi and bacteria has primarily focused on finding one protease with efficient keratinase activity. Recently, an investigation was conducted of all keratinases secreted from a fungus known to grow on keratinaceous materials, such as feather, horn, and hooves. The study demonstrated that a minimum of three keratinases is needed to break down keratin, an endo-acting, an exo-acting, and an oligopeptide-acting keratinase. Further, several studies have documented that disruption of sulfur bridges of the keratin structure acts synergistically with the keratinases to loosen the molecular structure, thus giving the enzymes access to their substrate, the protein structure. With such complexity, it is relevant to compare microbial keratin decomposition with the microbial decomposition of well-studied polymers such as cellulose and chitin. Interestingly, it was recently shown that the specialized enzymes, lytic polysaccharide monoxygenases (LPMOs), shown to be important for breaking the recalcitrance of cellulose and chitin, are also found in keratin-degrading fungi. A holistic view of the complex molecular self-assembling structure of keratin and knowledge about enzymatic and boosting factors needed for keratin breakdown have been used to formulate a hypothesis for mode of action of the LPMOs in keratin decomposition and for a model for degradation of keratin in nature. Testing such hypotheses and models still needs to be done. Even now, the hypothesis can serve as an inspiration for designing industrial processes for keratin decomposition for conversion of unexploited waste streams, chicken feather, and pig bristles into bioaccessible animal feed.

Extracellular peptidases from Deinococcus radiodurans

The extremophile Deinococcus radiodurans wild type R1 produces peptidases (metallo- and serine-) in TGY medium and in the media supplemented with human hair (HMY) and chicken feathers (FMY). Enzymatic screening on agar plates revealed peptidase activity. In TGY medium metallopeptidases were detected corresponding to a molecular mass range of 300-85 kDa (gelatinases); 280-130 (caseinases) and a 300 and a 170 kDa (keratinases); and a gelatinolytic serine peptidase (75 kDa). In HMY medium after 144 h, D. radiodurans produced keratinase (290 U/ml), gelatinase (619 U/ml) and sulfite (26 µg/ml). TGY medium produced higher proteolytic activity: 950 U/ml of gelatinolytic (24 h); 470 U/ml of keratinolytic (24 h) and 110 U/ml of caseinolytic (72 h). In the FMY medium, we found gelatinolytic (317 U/ml), keratinolytic (43 U/ml) and caseinolytic (85 U/ml) activities. The sulfite had a maximum release at 48 h (8.1 µg/ml). Enzymography analysis revealed that the keratinases degraded keratin after 24 h of reaction. The addition of sodium sulfite (1.0 %) improved the keratin degradation. Environmental Scanning Electron microscopy revealed alterations such as damage and holes in the hair fiber cuticle after D. radiodurans growth. This work presents for the first time D. radiodurans as a new keratinolytic microorganism.