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

Enhancing spinach growth with a biofertilizer derived from chicken feathers using a keratinolytic bacterial consortium

This study was conducted to develop a cost-effective and environmentally friendly biofertilizer by utilizing chicken feather waste. Two bacterial strains were employed to biotransform the abundant keratin protein in feathers. The keratinolytic bacterial strains used in this study were identified as Bacillus licheniformis MW45 and Bacillus paralicheniformis MW48. The feather hydrolysate was assessed for its effectiveness as a nitrogen fertilizer with slow-release properties. The study employed a completely randomized design (CRD) with three replicates, and statistical analysis, including ANOVA followed by Tukey's test, was used to validate the differences between treatments. The test plant was spinach, and various growth parameters were observed. The growth promotion activity of the produced biofertilizer was compared with a commercially available NPK fertilizer. The results showed that the growth promotion effect of chicken feather hydrolysate was significantly higher than the control and commercially available NPK fertilizer. The feather hydrolysate displayed the highest germination percentage (48%), vigor index (1081.44), number of leaves (17), height (22.53 cm), and weight (3.493 g), compared to the chemical fertilizer's germination percentage (31%), vigor index (714.4), number of leaves (13), height (18.5 cm), and weight (1.904 g). Statistical analysis showed that the fermented chicken feather hydrolysate can be effectively applied as a slow-releasing nitrogen fertilizer in agricultural fields. The novelty of this study lies in the use of a bacterial consortium to transform chicken feathers into high efficiency biofertilizer. This production may not only supports the national economy by increasing crop yield but also contributes to a cleaner and greener Pakistan by recycling feather waste.

Enhanced Synthesis, Purification, and Characterization of a Marine Bacterial Consortium-Derived Protease Enzyme With Destaining and Keratinolytic Activity

Two marine-derived bacteria, Bacillus paralicheniformis (HR-1) and Bacillus haynesii (HR-5), were isolated from sediments and identified using 16S ribosomal RNA gene amplification and sequencing as well as biochemical analysis. The development of a bacterial consortium (HR-1 & HR-5) from these two bacteria was used to increase the production of the protease enzyme under various conditions, including fermentation media, carbon and nitrogen sources (1% w/v), different pH levels, incubation time, and the obtained enzyme, were detected using SDS-PAGE followed by purification. Bacterial consortium HR-1 & HR-5 exhibited maximum protease production (330.42 ± 4.47 U/mL) than the individual isolates HR-1 (156.32 ± 2.14 U/mL) and HR-5 (185.73 ± 5.14 U/mL) on supplementing peptone (1% w/v), 2.8% skim milk + N-broth, pH 9, and dextrose (1% w/v) after 48 h of incubation time. The purified enzyme showed increased activity at alkaline pH 9.0 and also in the presence of ions such as Ca+2, Fe+3, Mg+2, and Mn+2. The purified protease obtained from the consortium HR-1 and HR-5 shows improved efficiency for stain removal from cloth as well as high keratinolytic efficiency for poultry feather degradation, making this enzyme suitable for industrial use, particularly in the textile and tannery sectors.

Unraveling dynamics and interactions of core microorganisms in the biodegradation of keratin-based feather wastes

Waste feathers, abundant byproducts of the poultry industry, pose significant environmental challenges. Although microbial degradation has been investigated, the core microorganisms and their interactions remain underexplored. This study examined microbial community dynamics during feather degradation, using diverse feather sources and under varying temperatures. Significant divergences were observed in bacterial communities, with Firmicutes, Actinobacteria, and Acidobacteriota (56.65%, 18.13%, and 11.14%) as dominant phyla. A core microbial consortium of 51 taxa was identified, with 8 core genera from the Bacilli class, significantly enriched during degradation. Higher temperature (50 °C) accelerated degradation. Dynamics patterns showed the enrichment of and depletion of some strains. Functional prediction highlighted the mechanisms for keratin biodegradation. This study identified core microorganisms and enzymes during keratin degradation, providing evidence to microbial treatment of keratin-based waste to reduce agricultural pollution.

Transcriptomics Reveals the Mechanism of Purpureocillium lilacinum GZAC18-2JMP in Degrading Keratin Material

Microbial degradation of keratin is characterized by its inherent safety, remarkable efficiency, and the production of copious degradation products. All these attributes contribute to the effective management of waste materials at high value-added and in a sustainable manner. Microbial degradation of keratin materials remains unclear, however, with variations observed in the degradation genes and pathways among different microorganisms. In this study, we sequenced the transcriptome of Purpureocillium lilacinum GZAC18-2JMP mycelia on control medium and the medium containing 1% feather powder, analyzed the differentially expressed genes, and revealed the degradation mechanism of chicken feathers by P. lilacinum GZAC18-2JMP. The results showed that the chicken feather degradation rate of P. lilacinum GZAC18-2JMP reached 64% after 216 h of incubation in the fermentation medium, reaching a peak value of 148.9 μg·mL-1 at 192 h, and the keratinase enzyme activity reached a peak value of 211 U·mL-1 at 168 h, which revealed that P. lilacinum GZAC18-2JMP had a better keratin degradation effect. A total of 1001 differentially expressed genes (DEGs) were identified from the transcriptome database, including 475 upregulated genes and 577 downregulated genes. Kyoto encyclopedia of genes and genomes (KEGG) enrichment analysis of the DEGs revealed that the metabolic pathways related to keratin degradation were mainly sulfur metabolism, ABC transporters, and amino acid metabolism. Therefore, the results of this study provide an opportunity to gain further insight into keratin degradation and promote the biotransformation of feather wastes.

Biodegradation of Keratin Waste by Bacillus velezensis HFS_F2 through Optimized Keratinase Production Medium

Enormous aggregates of keratinous wastes are produced annually by the poultry and leather industries which cause environmental degradation globally. To combat this issue, microbially synthesized extracellular proteases known as keratinase are used widely which is effective in degrading keratin found in hair and feathers. In the present work, keratinolytic bacteria were isolated from poultry farm soil and feather waste, and various cultural conditions were optimized to provide the highest enzyme production for efficient keratin waste degradation. Based on the primary and secondary screening methods, the potent keratinolytic strain (HFS_F2T) with the highest enzyme activity 32.65 ± 0.16 U/mL was genotypically characterized by 16S rRNA sequencing and was confirmed as Bacillus velezensis HFS_F2T ON556508. Through one-variable-at-a-time approach (OVAT), the keratinase production medium was optimized with sucrose (carbon source), beef extract (nitrogen source) pH-7, inoculum size (5%), and incubation at 37 °C). The degree of degradation (%DD) of keratin wastes was evaluated after 35 days of degradation in the optimized keratinase production medium devoid of feather meal under submerged fermentation conditions. Further, the deteriorated keratin wastes were visually examined and the hydrolysed bovine hair with 77.32 ± 0.32% degradation was morphologically analysed through Field Emission Scanning Electron Microscopy (FESEM) to confirm the structural disintegration of the cuticle. Therefore, the current study would be a convincing strategy for reducing the detrimental impact of pollutants from the poultry and leather industries by efficient keratin waste degradation through the production of microbial keratinase.

Molecular strategies to enhance the keratinase gene expression and its potential implications in poultry feed industry

The tons of keratin waste are produced by the poultry and meat industry which is an insoluble and protein-rich material found in hair, feathers, wool, and some epidermal wastes. These waste products could be degraded and recycled to recover protein, which can save our environment. One of the potential strategy to achieve this target is use of microbial biotreatment which is more convenient, cost-effective, and environment-friendly by formulating hydrolysate complexes that could be administered as protein supplements, bioactive peptides, or animal feed ingredients. Keratin degradation shows great promise for long-term protein and amino acid recycling. According to the MEROPS database, known keratinolytic enzymes currently belong to at least 14 different protease families, including S1, S8, S9, S10, S16, M3, M4, M14, M16, M28, M32, M36, M38, and M55. In addition to exogenous attack (proteases from families S9, S10, M14, M28, M38, and M55), the various keratinolytic enzymes also function via endo-attack (proteases from families S1, S8, S16, M4, M16, and M36). Biotechnological methods have shown great promise for enhancing keratinase expression in different strains of microbes and different protein engineering techniques in genetically modified microbes such as bacteria and some fungi to enhance keratinase production and activity. Some microbes produce specific keratinolytic enzymes that can effectively degrade keratin substrates. Keratinases have been successfully used in the leather, textile, and pharmaceutical industries. However, the production and efficiency of existing enzymes need to be optimized before they can be used more widely in other processes, such as the cost-effective pretreatment of chicken waste. These can be improved more effectively by using various biotechnological applications which could serve as the best and novel approach for recycling and degrading biomass. This paper provides practical insights about molecular strategies to enhance keratinase expression to effectively utilize various poultry wastes like feathers and feed ingredients like soybean pulp. Furthermore, it describes the future implications of engineered keratinases for environment friendly utilization of wastes and crop byproducts for their better use in the poultry feed industry.

Andean soil-derived lignocellulolytic bacterial consortium as a source of novel taxa and putative plastic-active enzymes

An easy and straightforward way to engineer microbial environmental communities is by setting up liquid enrichment cultures containing a specific substrate as the sole source of carbon. Here, we analyzed twenty single-contig high-quality metagenome-assembled genomes (MAGs) retrieved from a microbial consortium (T6) that was selected by the dilution-to-stimulation approach using Andean soil as inoculum and lignocellulose as a selection pressure. Based on genomic metrics (e.g., average nucleotide and amino acid identities) and phylogenomic analyses, 15 out of 20 MAGs were found to represent novel bacterial species, with one of those (MAG_26) belonging to a novel genus closely related to Caenibius spp. (Sphingomonadaceae). Following the rules and requirements of the SeqCode, we propose the name Andeanibacterium colombiense gen. nov., sp. nov. for this taxon. A subsequent functional annotation of all MAGs revealed that MAG_7 (Pseudobacter hemicellulosilyticus sp. nov.) contains 20, 19 and 16 predicted genes from carbohydrate-active enzymes families GH43, GH2 and GH92, respectively. Its lignocellulolytic gene profile resembles that of MAG_2 (the most abundant member) and MAG_3858, both of which belong to the Sphingobacteriaceae family. Using a database that contains experimentally verified plastic-active enzymes (PAZymes), twenty-seven putative bacterial polyethylene terephthalate (PET)-active enzymes (i.e., alpha/beta-fold hydrolases) were detected in all MAGs. A maximum of five putative PETases were found in MAG_3858, and two PETases were found to be encoded by A. colombiense. In conclusion, we demonstrate that lignocellulose-enriched liquid cultures coupled with genome-resolved metagenomics are suitable approaches to unveil the hidden bacterial diversity and its polymer-degrading potential in Andean soil ecosystems.

Isolation of a novel feather-degrading Ectobacillus sp. JY-23 strain and characterization of a new keratinase in the M4 metalloprotease family

Microbial keratinases have prominent potential in biotransformation of recalcitrant keratin substrates to value-added products which has made keratinases a research focus in the past decades. In this study, an efficient feather-degrading bacterium was isolated and identified as a novel species in Ectobacillus genus and designated as Ectobacillus sp. JY-23. The degradation characteristics analysis revealed that Ectobacillus sp. JY-23 could utilize chicken feathers (0.4% w/v) as the sole nutrient source and degraded 92.95% of feathers in 72 h. A significant increase in sulfite and free sulfydryl group content detected in the feather hydrolysate (culture supernatant) indicated efficient reduction of disulfide bonds, which inferred that the degradation mechanism of isolated strain was a synergetic action of sulfitolysis and proteolysis. Moreover, abundant amino acids were also detected, among which proline and glycine were the predominant free amino acids. Then, the keratinase of Ectobacillus sp. JY-23 was mined and Y1_15990 was identified as the keratinase encoding gene of Ectobacillus sp. JY-23 and designated as kerJY-23. Escherichia coli strain overexpressing kerJY-23 degraded chicken feathers in 48 h. Finally, bioinformatics prediction of KerJY-23 demonstrated that it belonged to the M4 metalloprotease family, which was a third keratinase member in this family. KerJY-23 showed low sequence identity to the other two keratinase members, indicating the novelty of KerJY-23. Overall, this study presents a novel feather-degrading bacterium and a new keratinase in the M4 metalloprotease family with remarkable potential in feather keratin valorization.

Enhancement of feather degrading keratinase of Streptomyces swerraensis KN23, applying mutagenesis and statistical optimization to improve keratinase activity

In this study, 25 actinomyces isolates were obtained from 10 different poultry farms and tested for their keratinase activity. The isolate with the highest keratinase activity was identified through molecular identification by PCR and sequencing of the 16S rRNA gene to be Streptomyces spp. and was named Streptomyces werraensis KN23 with an accession number of OK086273 in the NCBI database. Sequential mutagenesis was then applied to this strain using UV, H2O2, and SA, resulting in several mutants. The best keratinolytic efficiency mutant was designated as SA-27 and exhibited a keratinase activity of 106.92 U/ml. To optimize the keratinase expression of mutant SA-27, the Response Surface Methodology was applied using different parameters such as incubation time, pH, carbon, and nitrogen sources. The optimized culture conditions resulted in a maximum keratinase specific activity of 129.60 U/ml. The genetic diversity of Streptomyces werraensis KN23 wild type compared with five mutants was studied using Inter-simple sequence repeat (ISSR). The highest total and polymorphic unique bands were revealed in the S. werraensis KN23 and SA-18 mutant, with 51 and 41 bands, respectively. The dendrogram based on combined molecular data grouped the Streptomyces werraensis and mutants into two clusters. Cluster I included SA-31 only, while cluster II contained two sub-clusters. Sub-cluster one included SA-27, and sub-cluster two included SA-26. The sub-cluster two divided into two sub-sub clusters. Sub-sub cluster one included SA-18, while sub-sub cluster two included one group (SA-14 and S. werraensis KN23).

Novel bacterial taxa in a minimal lignocellulolytic consortium and their potential for lignin and plastics transformation

The understanding and manipulation of microbial communities toward the conversion of lignocellulose and plastics are topics of interest in microbial ecology and biotechnology. In this study, the polymer-degrading capability of a minimal lignocellulolytic microbial consortium (MELMC) was explored by genome-resolved metagenomics. The MELMC was mostly composed (>90%) of three bacterial members (Pseudomonas protegens; Pristimantibacillus lignocellulolyticus gen. nov., sp. nov; and Ochrobactrum gambitense sp. nov) recognized by their high-quality metagenome-assembled genomes (MAGs). Functional annotation of these MAGs revealed that Pr. lignocellulolyticus could be involved in cellulose and xylan deconstruction, whereas Ps. protegens could catabolize lignin-derived chemical compounds. The capacity of the MELMC to transform synthetic plastics was assessed by two strategies: (i) annotation of MAGs against databases containing plastic-transforming enzymes; and (ii) predicting enzymatic activity based on chemical structural similarities between lignin- and plastics-derived chemical compounds, using Simplified Molecular-Input Line-Entry System and Tanimoto coefficients. Enzymes involved in the depolymerization of polyurethane and polybutylene adipate terephthalate were found to be encoded by Ps. protegens, which could catabolize phthalates and terephthalic acid. The axenic culture of Ps. protegens grew on polyhydroxyalkanoate (PHA) nanoparticles and might be a suitable species for the industrial production of PHAs in the context of lignin and plastic upcycling.

Genome-wide analysis of Keratinibaculum paraultunense strain KD-1 T and its key genes and metabolic pathways involved in the anaerobic degradation of feather keratin

Keratinibaculum paraultunense strain KD-1 ^T (= JCM 18769 ^T = DSM 26752 ^T) is a strictly anaerobic rod-shaped bacterium. Under optimal conditions, feather keratin can be completely degraded by strain KD-1 within 24 h. Genomic sequencing showed that the genome was a single circular chromosome consisting of 2,307,997 base pairs (bp), with an average G + C content of 29.8% and no plasmids. A total of 2308 genes were annotated, accounting for 88.87% of the genomic sequence, and 1495 genes were functionally annotated. Among these, genes Kpa0144, Kpa0540, and Kpa0541 encoding the thioredoxin family members were identified, and may encode the potential disulfide reductases, with redox activity for protein disulfide bonds. Two potential keratinase-encoding genes, Kpa1675 and Kpa2139, were also identified, and corresponded to the ability of strain KD-1 to hydrolyze keratin. Strain KD-1 encoded genes involved in the heterotrophic metabolic pathways of 14 amino acids and various carbohydrates. The metabolic pathways for amino acid and carbohydrate metabolism were mapped in strain KD-1 based on KEGG annotations. The complete genome of strain KD-1 provided fundamental data for the further investigation of its physiology and genetics.

Bacillus amyloliquefaciens CU33 fermented feather meal-soybean meal product improves the intestinal morphology to promote the growth performance of broilers

This study is aimed to select optimum keratin degradation ability from Bacillus strains for feather meal-soybean meal fermentation, and favorably water content for the strain during fermentation of feather meal-soybean meal, and finally investigate the effects of the fermented feather meal-soybean meal product (FFSMP) on growth performance, carcass trait, clinical blood biochemistry, and intestinal morphology of broilers. Thirty-six bacteria strains from soil, sewage pool, and feather waste were screened and selected Bacillus subtilis var. natto N21 (N21), B. subtilis CU14 (CU14), and B. amyloliquefaciens CU33 (CU33) with better keratinase activity and feather-degrading rate. The result of trial 1 showed that the FFSMP produced by CU33 had the optimum physiochemical characterizations, amino acid composition and feeding performance for broilers. Hence the effects of water content (45, 50, 55, and 60%) on FFMSP fermentation of CU33 were investigated in trial 2. Result showed that pH value, counts of Bacillus-like bacteria, γ-PGA, viscosity, surfactin yield and odor all significantly increased according to the water content (P < 0.05). The protease activity reached significantly highest in the 55% and 60% water content groups (P < 0.01). The broilers performance of 55% and 60% water content group were significantly higher than control group (P < 0.05) in weight gain (WG), feed intake (b) at 0 to 21-d-old and the WG, feed conversion ratio (FCR), and production efficiency factor at 0 to 35-d-old, and could reach the similar growth performance as fish meal group (P > 0.05). The fermentation groups significantly decreased urea nitrogen (P < 0.05) and increased creatinine (P < 0.05) in the blood. The fermentation groups also significantly decreased the crypt depth in the duodenum (P < 0.05) and increased villus height to crypt depth ratio of the duodenum (P < 0.05). In conclusion, CU33 shows the best degradation rate for feather and keratinase activity, and the FFSMP with a water content of 50% to 60% during fermentation is suggested. Diets supplemented with 5% FFSMP can promote the growth of broilers by improving the morphology of the duodenum and achieve the feeding effect of high-quality fish meal.

Perspectives on Converting Keratin-Containing Wastes Into Biofertilizers for Sustainable Agriculture

Keratin-containing wastes become pollution to the environment if they are not treated properly. On the other hand, these wastes can be converted into value-added products applicable to many fields. Organic fertilizers and biofertilizers are important for sustainable agriculture by providing nutrients to enhance the growth speed of the plant and production. Keratin-containing wastes, therefore, will be an important resource to produce organic fertilizers. Many microorganisms exhibit capabilities to degrade keratins making them attractive to convert keratin-containing wastes into valuable products. In this review, the progress in microbial degradation of keratins is summarized. In addition, perspectives in converting keratin into bio- and organic fertilizers for agriculture are described. With proper treatment, feather wastes which are rich in keratin can be converted into high-value fertilizers to serve as nutrients for plants, reduce environmental pressure and improve the quality of the soil for sustainable agriculture.

Chryseobacterium aquifrigidense FANN1 Produced Detergent-Stable Metallokeratinase and Amino Acids Through the Abasement of Chicken Feathers

Microbial keratinases’ versatility in the beneficiation of keratinous waste biomass into high-value products prompts their application in diverse spheres hence, advancing green technology and the bioeconomy. Consequently, a feather-degrading Chryseobacterium aquifrigidense FANN1 (NCBI: MW169027) was used to produce keratinase, and its biochemical properties were determined. The optimization of physicochemical parameters and analysis of the free amino acid constituents of the feather hydrolysate were also carried out. FANN1 showed a maximum keratinase yield of 1,664.55 ± 42.43 U/mL after 72 h, at optimal process conditions that included initial medium pH, incubation temperature, inoculum size, and chicken feather concentration of 8, 30°C, 4% (v/v), and 15 (g/L), respectively. Analysis of degradation product showed 50.32% and 23.25% as the protein value and total free amino acids, respectively, with a relatively high abundance of arginine (2.25%) and serine (2.03%). FANN1 keratinase was optimally active at pH 8.0 and relatively moderate to high temperature (40–50°C). EDTA and 1,10-phenanthroline inhibited the keratinase activity, and that suggests a metallo-keratinase. The enzyme showed remarkable stability in the presence of chemical agents, with residual activity 141 ± 10.38%, 98 ± 0.43%, 111 ± 1.73%, 124 ± 0.87%, 104 ± 3.89%, 107 ± 7.79%, and 112 ± 0.86% against DTT, H₂O₂, DMSO, acetonitrile, triton X-100, tween-80, and SDS, respectively. The residual activity of FANN1 keratinase was enhanced by Sunlight (129%), Ariel (116%), MAQ (151%), and Surf (143%) compared to the control after 60 min preincubation. Likewise, the enzyme was remarkably stable in the presence Fe³⁺ (120 ± 5.06%), Ca²⁺ (100 ± 10.33%), Na⁺ (122 ± 2.95%), Al³⁺ (106 ± 10.33%); while Co²⁺ (68 ± 8.22%) and Fe²⁺ (51 ± 8.43%) elicited the most repressive effect on keratinase activity. The findings suggest that C. aquifrigidense FANN1 is a potential candidate for keratinous wastes bio-recycling, and the associated keratinase has a good prospect for application in detergent formulation.

Engineering complex communities by directed evolution

Directed evolution has been used for decades to engineer biological systems at or below the organismal level. Above the organismal level, a small number of studies have attempted to artificially select microbial ecosystems, with uneven and generally modest success. Our theoretical understanding of artificial ecosystem selection is limited, particularly for large assemblages of asexual organisms, and we know little about designing efficient methods to direct their evolution. Here, we have developed a flexible modelling framework that allows us to systematically probe any arbitrary selection strategy on any arbitrary set of communities and selected functions. By artificially selecting hundreds of in silico microbial metacommunities under identical conditions, we first show that the main breeding methods used to date, which do not necessarily let communities reach their ecological equilibrium, are outperformed by a simple screen of sufficiently mature communities. We then identify a range of alternative directed evolution strategies that, particularly when applied in combination, are well suited for the top-down engineering of large, diverse and stable microbial consortia. Our results emphasize that directed evolution allows an ecological structure-function landscape to be navigated in search of dynamically stable and ecologically resilient communities with desired quantitative attributes.

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.

Use and treatment of chicken feathers as a natural adsorbent for the removal of copper in aqueous solution

PURPOSE

Copper is a heavy metal that causes considerable deterioration to human health and ecosystems, so their elimination in water bodies is of great interest. Present investigation shows the efficiency of chicken feather as a natural adsorbent and its subsequent degradation in order to have an integral treatment and avoid the unconscious disposition.

METHODS

Optimal conditions of adsorption process were determined using the Response Surface Methodology (RSM)-Box-Behnken design (BBD) with three variables (pH, temperature and adsorbent dose). After that, the optimal conditions were used to analize the adsorption isotherms by Langmuir, Freundlich and Temkin models; also thermodynamics parameters Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were obtained. Finally, the biodegradation of the residue denominated "adsorbent-adsorbate" complex was evaluated through monitoring the soluble protein production, keratinolytic activity, ninhydrin positive products, sulfhydryl groups, and gravimetrically analysis.

RESULTS

The optimum conditions for the adsorption were 30°C and pH 3, the Langmuir model was better described the adsorption process at 30°C, while at 40°C was Temkin model. The chicken feather turned out a natural adsorbent competitive with respect to others used in the removal of copper in liquid systems; obtaining qmax of 7.84 and 11.48 mg/g at 30 and 40°C, respectively; it was also a favorable and spontaneous process. Finally the adsorbent used was degraded by a keratinolytic consortium.

CONCLUSIONS

In this study, chicken feather was used as a low cost adsorbent for copper efficiently and with the feasibility that the adsorbent can be biodegraded and release the metal.

Comparative Genomics Analysis of Keratin-Degrading Chryseobacterium Species Reveals Their Keratinolytic Potential for Secondary Metabolite Production

A promising keratin-degrading strain from the genus Chryseobacterium (Chryseobacterium sp. KMC2) was investigated using comparative genomic tools against three publicly available reference genomes to reveal the keratinolytic potential for biosynthesis of valuable secondary metabolites. Genomic features and metabolic potential of four species were compared, showing genomic differences but similar functional categories. Eleven different secondary metabolite gene clusters of interest were mined from the four genomes successfully, including five common ones shared across all genomes. Among the common metabolites, we identified gene clusters involved in biosynthesis of flexirubin-type pigment, microviridin, and siderophore, showing remarkable conservation across the four genomes. Unique secondary metabolite gene clusters were also discovered, for example, ladderane from Chryseobacterium sp. KMC2. Additionally, this study provides a more comprehensive understanding of the potential metabolic pathways of keratin utilization in Chryseobacterium sp. KMC2, with the involvement of amino acid metabolism, TCA cycle, glycolysis/gluconeogenesis, propanoate metabolism, and sulfate reduction. This work uncovers the biosynthesis of secondary metabolite gene clusters from four keratinolytic Chryseobacterium species and shades lights on the keratinolytic potential of Chryseobacterium sp. KMC2 from a genome-mining perspective, can provide alternatives to valorize keratinous materials into high-value bioactive natural products.

Metagenomic analysis of a keratin-degrading bacterial consortium provides insight into the keratinolytic mechanisms

Keratin is an insoluble fibrous protein from natural environments, which can be recycled to value-added products by keratinolytic microorganisms. A microbial consortium with efficient keratinolytic activity was previously enriched from soil, but the genetic basis behind its remarkable degradation properties was not investigated yet. To identify the metabolic pathways involved in keratinolysis and clarify the observed synergy among community members, shotgun metagenomic sequencing was performed to reconstruct metagenome-assembled genomes. More than 90% genera of the enriched bacterial consortium were affiliated to Chryseobacterium, Stenotrophomonas, and Pseudomonas. Metabolic potential and putative keratinases were predicted from the metagenomic annotation, providing the genetic basis of keratin degradation. Furthermore, metabolic pathways associated with keratinolytic processes such as amino acid metabolism, disulfide reduction and urea cycle were investigated from seven high-quality metagenome-assembled genomes, revealing the potential metabolic cooperation related to keratin degradation. This knowledge deepens the understanding of microbial keratinolytic mechanisms at play in a complex community, pinpointing the significance of synergistic interactions, which could be further used to optimize industrial keratin degradation processes.

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.

Azo dying of α-keratin material improves microbial keratinase screening and standardization

Microbial conversion through enzymatic reactions has received a lot of attention as a cost-effective and environmentally friendly way to recover amino acids and short peptides from keratin materials. However, accurate assessment of microbial keratinase activity is not straightforward, and current available methods lack sensitivity and standardization. Here, we suggest an optimized Azokeratin assay, with substrate generated directly from azo-dyed raw keratin material. We introduced supernatant filtration in the protocol for optimal stopping of keratinase reactions instead of the widely used trichloroacetic acid (TCA), as it generated biases and impacted the sensitivity. We furthermore suggest a method for standardization of keratinase activity signals using proteinase K, a well-known keratinase, as a reference enabling reproducibility between studies. Lastly, we evaluated our developed method with several bacterial isolates through benchmarking against a commercial assay (Keratin Azure). Under different setups, the Azokeratin method was more sensitive than commonly used Keratin Azure-based assays (3-fold). We argue that this method could be applied with any type of keratin substrate, enabling more robust and sensitive results which can be used for further comparison with other studies, thus representing an important progress within the field of microbial keratin degradation.

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.

Biochemical characterisation and application of keratinase from Bacillus thuringiensis MT1 to enable valorisation of hair wastes through biosynthesis of vitamin B-complex

This study reports on the exploitation of keratinous hydrolysate by keratinase enzymes to produce vitamin B-complex. Toward this end, keratinase enzyme was produced by Bacillus thuringiensis strain MT1, newly isolated from cattle-yard utilising donkey hairs. Scanning electron microscope (SEM) and Fourier transform infrared spectrophotometer (FTIR) analyses demonstrated hairs disintegration and the disruption of the disulphide bonds of the keratin structure, respectively. The biochemical characterisation of the produced enzyme exhibited optimal activity of 422 U/ml at 50 °C and pH 9 with a molecular mass of 80 kDa. The enzyme activity was entirely deactivated by Ethylenediaminetetraacetic acid (EDTA), implying the existence of a metallokeratinase group. Donkey hairs were thus treated with metallokeratinase, emancipating eight essential and eight more non-essential amino acids, which were identified employing amino acid analyser. These amino acids were subsequently utilised by Saccharomyces cerevisiae strain ATCC 64712, at different concentrations, to produce vitamin B-complex. High-performance liquid chromatography (HPLC) analysis revealed the synthesis of vitamins B1, B2, and B12 at various levels associated with concentrations of supplemented amino acids. This report thus highlights the feasible application of keratinase enzyme as an eco-friendly approach to managing hair waste, and concurrently promotes the implementation of hair-based hydrolysate in vitamin B-complex biosynthesis.

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.

Improving the Performance of Feather Keratin/Polyvinyl Alcohol/Tris(hydroxymethyl)Aminomethane Nanocomposite Films by Incorporating Graphene Oxide or Graphene

In this study, feather keratin/polyvinyl alcohol/tris(hydroxymethyl)aminomethane (FK/PVA/Tris) bionanocomposite films containing graphene oxide (GO) (0.5, 1, 2, and 3 wt%) or graphene (0.5, 1, 2, and 3 wt%) were prepared using a solvent casting method. The scanning electron microscopy results indicated that the dispersion of GO throughout the film matrix was better than that of graphene. The successful formation of new hydrogen bonds between the film matrix and GO was confirmed through the use of Fourier-transform infrared spectroscopy. The tensile strength, elastic modulus, and initial degradation temperature of the films increased, whereas the total soluble mass, water vapor permeability, oxygen permeability, and light transmittance decreased following GO or graphene incorporation. In summary, nanoblending is an effective method to promote the application of FK/PVA/Tris-based blend films in the packaging field.

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

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

Community-intrinsic properties enhance keratin degradation from bacterial consortia

Although organic matter may accumulate sometimes (e.g. lignocellulose in peat bog), most natural biodegradation processes are completed until full mineralization. Such transformations are often achieved by the concerted action of communities of interacting microbes, involving different species each performing specific tasks. These interactions can give rise to novel "community-intrinsic" properties, through e.g. activation of so-called "silent genetic pathways" or synergistic interplay between microbial activities and functions. Here we studied the microbial community-based degradation of keratin, a recalcitrant biological material, by four soil isolates, which have previously been shown to display synergistic interactions during biofilm formation; Stenotrophomonas rhizophila, Xanthomonas retroflexus, Microbacterium oxydans and Paenibacillus amylolyticus. We observed enhanced keratin weight loss in cultures with X. retroflexus, both in dual and four-species co-cultures, as compared to expected keratin degradation by X. retroflexus alone. Additional community intrinsic properties included accelerated keratin degradation rates and increased biofilm formation on keratin particles. Comparison of secretome profiles of X. retroflexus mono-cultures to co-cultures revealed that certain proteases (e.g. serine protease S08) were significantly more abundant in mono-cultures, whereas co-cultures had an increased abundance of proteins related to maintaining the redox environment, e.g. glutathione peroxidase. Hence, one of the mechanisms related to the community intrinsic properties, leading to enhanced degradation from co-cultures, might be related to a switch from sulfitolytic to proteolytic functions between mono- and co-cultures, respectively.

Construction of Simplified Microbial Consortia to Degrade Recalcitrant Materials Based on Enrichment and Dilution-to-Extinction Cultures

The capacity of microbes to degrade recalcitrant materials has been extensively explored for environmental remediation and industrial production. Significant achievements have been made with single strains, but focus is now going toward the use of microbial consortia owning to their functional stability and efficiency. However, assembly of simplified microbial consortia (SMC) from complex environmental communities is still far from trivial due to large diversity and the effect of biotic interactions. Here we propose a strategy, based on enrichment and dilution-to-extinction cultures, to construct SMC with reduced diversity for degradation of keratinous materials. Serial dilutions were performed on a keratinolytic microbial consortium pre-enriched from a soil sample, monitoring the dilution effect on community growth and enzymatic activities. An appropriate dilution regime (10-9) was selected to construct a SMC library from the enriched microbial consortium. Further sequencing analysis and keratinolytic activity assays demonstrated that obtained SMC displayed actual reduced microbial diversity, together with various taxonomic composition, and biodegradation capabilities. More importantly, several SMC possessed equivalent levels of keratinolytic efficiency compared to the initial consortium, showing that simplification can be achieved without loss of function and efficiency. This methodology is also applicable to other types of recalcitrant material degradation involving microbial consortia, thus considerably broadening its application scope.

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.

Improving Thermal, Mechanical, and Barrier Properties of Feather Keratin/Polyvinyl Alcohol/Tris(hydroxymethyl)aminomethane Nanocomposite Films by Incorporating Sodium Montmorillonite and TiO₂

In this study, feather keratin/polyvinyl alcohol/tris(hydroxymethyl)aminomethane (FK/PVA/Tris) bionanocomposite films containing two types of nanoparticles, namely one-dimensional sodium montmorillonite (MMT) clay platelets (0.5, 1, 3, and 5 wt%) and three-dimensional TiO₂ nanospheres (0.5, 1, 3, and 5 wt%), are prepared using solvent casting method. X-ray diffraction studies confirm the completely exfoliated structure of FK/PVA/Tris/MMT nanocomposites. The successful formation of new hydrogen bonds between the hydroxyl groups of the film matrix and the nanofillers is confirmed by Fourier transform infrared spectroscopy. The tensile strength, elongation at break, and initial degradation temperature of the films are enhanced after MMT and TiO₂ incorporation. The water vapor permeability, oxygen permeability, and light transmittance decrease with increase in TiO₂ and MMT contents. In summary, nanoblending is an effective method to promote the application of FK/PVA/Tris blend films in the packaging field.

Improving the Water Resistance and Mechanical Properties of Feather Keratin/Polyvinyl Alcohol/Tris(Hydroxymethyl)Aminomethane Blend Films by Cross-Linking with Transglutaminase, CaCl₂, and Genipin

The high moisture sensitivity of feather keratin/polyvinyl alcohol/tris(hydroxymethyl)aminomethane (FK/PVA/Tris) blend films hinders their application in the packaging field. Thus, in order to improve the water resistance and mechanical properties of such blend films, we attempted cross-linking the blend film with cross-linking agents such as transglutaminase (TG), CaCl₂, and genipin. Obvious differences in the morphology of the blended films were observed by scanning electron microscopy before and after cross-linking, indicating that cross-linking can inhibit the phase separation of the blend film. Conformational changes in the blend films after cross-linking were detected by Fourier transform infrared spectroscopy. Importantly, from examination of the total soluble mass, contact angle measurements, and water vapor permeability tests, it was apparent that cross-linking greatly improved the water resistance of the blend films, in addition to enhancing the mechanical properties (i.e., tensile strength and elongation at break). However, cross-linking was also found to reduce the oxygen barrier properties of the blend films. Therefore, cross-linking appears to be an effective method for promoting the application of FK/PVA/Tris blend films in the packaging field.