Novel serine keratinase from Caldicoprobacter algeriensis exhibiting outstanding hide dehairing abilities

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.

Study of nano-hydroxyapatite tagged alkaline protease isolated from Himalayan sub-alpine Forest soil bacteria and role in recalcitrant feather waste degradation

Purified calcium serine metalloprotease from Stenotrophomonas maltophilia strain SMPB12 exhibits highest enzyme activity at pH 9 and temperature range between 15 °C-25 °C. Enzyme supplemented with 40 μM Ca-Hap-NP (NP-protease) showed maximum elevated activity of 17.29 μmole/min/ml (1.9-fold of original protease activity). The thermostability of the enzyme was maintained for 1 h at 60 °C over an alkaline pH range 7.5-10, as compared to the NP untreated enzyme whose activity was of 8.97 μmole/min/ml. A significant loss of activity with EDTA (1.05 μmole/min/ml, 11.75 %), PMSF (0.93 μmole/min/ml, 10.46 %) and Hg2+ (3.81 μmole/min/ml, 42.49 %) was also observed. Kinetics study of NP-protease showed maximum decreases in Km (28.11 %) from 0.28 mM (NP untreated enzyme) to 0.22 mM (NP-protease) along with maximum increase in Vmax (42.88 %) from 1.25 μmole/min/ml to 1.79 μmole/min/ml at varying temperatures. The enhanced activity of NP-protease was able to efficiently degrade recalcitrant solid wastes like feather to produce value-added products like amino acids and helps in declogging recalcitrant solid wastes. The nano-enabled protease may be utilized in a smaller amount for degrading in bulk recalcitrant solid proteinaceous waste at 15 °C temperature as declogging agents providing an eco-friendly efficient process.

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

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

Complete genome sequence of Bacillus Licheniformis NWMCC0046, a candidate for the laundry industry

In this study, selected properties of protease and the complete genome sequence of Bacillus licheniformis NWMCC0046 were investigated, to discover laundry applications and other potential probiotic properties of this strain. Partial characterization of B. licheniformis NWMCC0046 showed that its protease has good activity both in alkaline environments and at low temperatures. Also, the protease is compatible with commercial detergents and can be used as a detergent additive for effective stain removal at low temperatures. The complete genome sequence of B. licheniformis NWMCC0046 is comprised of a 4,321,565 bp linear chromosome with a G + C content of 46.78% and no plasmids. It had 4504 protein-encoding genes, 81 transfer RNA (tRNA) genes, and 24 ribosomal RNA (rRNA) genes. Genomic analysis revealed genes involved in exocellular enzyme production and probiotic properties. In addition, genomic sequence analysis revealed specific genes encoding carbohydrate metabolism pathways, resistance, and cold adaptation capacity. Overall, protease properties show its potential as a detergent additive enzyme. The complete genome sequence information of B. licheniformis NWMCC0046 was obtained, and functional prediction revealed its numerous probiotic properties.

Production and characterization of a new detergent-stable keratinase expressed by Pedobacter sp. 3.14.7, a novel Antarctic psychrotolerant keratin-degrading bacterium

BACKGROUND

Antarctica is one of the harshest environments in the world. Despite this fact, it has been colonized by microorganisms, which had to develop different adaptations in order to survive. By studying their enzymes, we can harness these adaptations in order to use them in various industrial processes. Keratinases (E.C. 3.4.99.11) are characterized by their robustness in withstanding extreme conditions and, along with other enzymes, are commonly added to laundry detergents, which makes their study of industrial interest.

RESULTS

In this work, a novel keratinase producer, Pedobacter sp. 3.14.7 (MF 347939.1), isolated from Antarctic birds' nests, was identified. This psychrotolerant isolate displays a typical psychrotolerant growth pattern, with an optimal temperature of 20 °C (μmax=0.23 h^-1). After 238 h, maximum proteolytic (22.00 ± 1.17 U ml^-1) and keratinolytic (33.04 ± 1.09 U ml^-1) activities were achieved with a feather sample conversion of approximately 85%. The keratinase present in crude extract was characterized as a metalloprotease with a molecular weight of 25 kDa, stable in a wide range of pH, with an optimum pH of 7.5. Optimum temperature was 55 °C. Wash performance at 20 °C using this crude extract could remove completely blood stain from cotton cloth.

CONCLUSION

We report a new keratinolytic bacteria from maritime Antarctica. Among its biochemical characteristics, its stability in the presence of different detergents and bleaching agents and its wash performance showed promising results regarding its potential use as a laundry detergent additive.

Genome sequence and Carbohydrate Active Enzymes (CAZymes) repertoire of the thermophilic Caldicoprobacter algeriensis TH7C1T

Background

Omics approaches are widely applied in the field of biology for the discovery of potential CAZymes including whole genome sequencing. The aim of this study was to identify protein encoding genes including CAZymes in order to understand glycans-degrading machinery in the thermophilic Caldicoprobacter algeriensis TH7C1^T strain.

Results

Caldicoprobacter algeriensis TH7C1^T is a thermophilic anaerobic bacterium belonging to the Firmicutes phylum, which grows between the temperatures of 55 °C and 75 °C. Next generation sequencing using Illumina technology was performed on the C. algeriensis strain resulting in 45 contigs with an average GC content of 44.9% and a total length of 2,535,023 bp. Genome annotation reveals 2425 protein-coding genes with 97 ORFs coding CAZymes. Many glycoside hydrolases, carbohydrate esterases and glycosyltransferases genes were found linked to genes encoding oligosaccharide transporters and transcriptional regulators; suggesting that CAZyme encoding genes are organized in clusters involved in polysaccharides degradation and transport. In depth analysis of CAZomes content in C. algeriensis genome unveiled 33 CAZyme gene clusters uncovering new enzyme combinations targeting specific substrates.

Conclusions

This study is the first targeting CAZymes repertoire of C. algeriensis, it provides insight to the high potential of identified enzymes for plant biomass degradation and their biotechnological applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-022-01818-0.

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

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

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

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

Bioinformatics based discovery of new keratinases in protease family M36

Keratinases are proteases that can catalyze the degradation of insoluble keratinous biomass. Keratinases in protease family M36 (MEROPS database) are endo-acting proteases. In total, 687 proteases are classified in family M36. In the present study, new keratinolytic enzymes were identified in protease family M36 using the bioinformatics tool Conserved Unique Peptide Patterns (CUPP). Via CUPP, M36 family members were classified into 11 groups, with CUPP group 1 containing the three currently known and sequenced family M36 keratinases (derived from the fungi Fusarium oxysporum, Microsporum canis and Onygena corvina) as well as an additional 71 uncharacterized M36 proteases. In order to assess the relevance of CUPP group 1 categorization to keratinolytic function, four uncharacterized M36 proteases and the known keratinase from F. oxysporum (in CUPP group 1) were selected for recombinant expression and keratinolytic activity assessment. The four hitherto unknown M36 proteases were from Phaeosphaeria nodorum, Aspergillus clavatus, Pseudogymnoascus pannorum and Nectria haematococca, and represent four different fungal taxonomical classes. The genes encoding the selected M36 proteases were individually expressed in Pichia pastoris and all proteases displayed keratinase activity on keratin azure. Additionally, the activity on different keratinase substrates, optimal reaction conditions and thermal stability were determined for the two most active new keratinases. The results validate the applicability of CUPP for function-based discovery of non-characterized keratinases and present new robust keratinases for potential use in keratin upgrading.

Molecular Identification of Keratinase DgokerA from Deinococcus gobiensis for Feather Degradation

Keratin is a tough fibrous structural protein that is difficult to digest with pepsin and trypsin because of the presence of a large number of disulfide bonds. Keratin is widely found in agricultural waste. In recent years, especially, the development of the poultry industry has resulted in a large accumulation of feather keratin resources, which seriously pollute the environment. Keratinase can specifically attack disulfide bridges in keratin, converting them from complex to simplified forms. The keratinase thermal stability has drawn attention to various biotechnological industries. It is significant to identify keratinases and improve their thermostability from microorganism in extreme environments. In this study, the keratinases DgoKerA was identified in Deinococcus gobiensis I-0 from the Gobi desert. The amino acid sequence analysis revealed that DgoKerA was 58.68% identical to the keratinase MtaKerA from M. thermophila WR-220 and 40.94% identical to the classical BliKerA sequence from B. licheniformis PWD-1. In vitro enzyme activity analysis showed that DgoKerA exhibited an optimum temperature of 60 °C, an optimum pH of 7 and a specific enzyme activity of 51147 U/mg. DgoKerA can degrade intact feathers at 60 °C and has good potential for industrial applications. The molecular modification of DgoKerA was also carried out using site-directed mutagenesis, in which the mutant A350S enzyme activity was increased by nearly 30%, and the results provide a theoretical basis for the development and optimization of keratinase applications.

Keratinases as Versatile Enzymatic Tools for Sustainable Development

To reduce anthropological pressure on the environment, the implementation of novel technologies in present and future economies is needed for sustainable development. The food industry, with dairy and meat production in particular, has a significant environmental impact. Global poultry production is one of the fastest-growing meat producing sectors and is connected with the generation of burdensome streams of manure, offal and feather waste. In 2020, the EU alone produced around 3.2 million tonnes of poultry feather waste composed primarily of keratin, a protein biopolymer resistant to conventional proteolytic enzymes. If not managed properly, keratin waste can significantly affect ecosystems, contributing to environmental pollution, and pose a serious hazard to human and livestock health. In this article, the application of keratinolytic enzymes and microorganisms for promising novel keratin waste management methods with generation of new value-added products, such as bioactive peptides, vitamins, prion decontamination agents and biomaterials were reviewed.

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

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

The keratinolytic bacteria Bacillus cytotoxicus as a source of novel proteases and feather protein hydrolysates with antioxidant activities

BACKGROUND

Argentina's geothermal areas are niches of a rich microbial diversity. In 2020, species of Bacillus cytotoxicus were isolated for the first time from these types of pristine natural areas. Bacillus cytotoxicus strains demonstrated the capability to grow and degrade chicken feathers with the concomitant production of proteases with keratinolytic activity, enzymes that have multitude of industrial applications. The aim of this research was to study the production of the proteolytic enzymes and its characterization. Also, feather protein hydrolysates produced during fermentation were characterized.

RESULTS

Among the thermotolerant strains isolated from the Domuyo geothermal area (Neuquén province, Argentina), Bacillus cytotoxicus LT-1 and Oll-15 were selected and put through submerged cultures using feather wastes as sole carbon, nitrogen, and energy source in order to obtain proteolytic enzymes and protein hydrolysates. Complete degradation of feathers was achieved after 48 h. Zymograms demonstrated the presence of several proteolytic enzymes with an estimated molecular weight between 50 and > 120 kDa. Optimum pH and temperatures of Bacillus cytotoxicus LT-1 crude extract were 7.0 and 40 °C, meanwhile for Oll-15 were 7.0 and 50 °C. Crude extracts were inhibited by EDTA and 1,10 phenanthroline indicating the presence of metalloproteases. Feather protein hydrolysates showed an interesting antioxidant potential measured through radical-scavenging and Fe³⁺-reducing activities.

CONCLUSION

This work represents an initial approach on the study of the biotechnological potential of proteases produced by Bacillus cytotoxicus. The results demonstrated the importance of continuous search for new biocatalysts with new characteristics and enzymes to be able to cope with the demands in the market.

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.

A Novel Thermostable Keratinase from Deinococcus geothermalis with Potential Application in Feather Degradation

Keratinase can specifically attack disulfide bridges in keratin to convert them from complex to simplified forms. Keratinase thermal stability has drawn attention to various biotechnological industries. In this study, a keratinase DgeKer was identified from a slightly thermophilic species, D. geothermalis. The in silico analysis showed that DgeKer is composed of signal peptide, N-terminal propeptide, mature domain, and C-terminal extension. DgeKer and its C-terminal extension-truncated enzyme (DgeKer-C) were cloned and expressed in E. coli. The purified DgeKer and DgeKer-C showed maximum activity at 70 °C and pH 9–The thermal stability assay (60 °C) showed that the half-life value of DgeKer and DgeKer-C were 103.45 min and 169.10 min, respectively. DgeKer and DgeKer-C were stable at the range of pH from 9 to 11 and showed good tolerance to some metal ions, surfactants and organic solvent. Furthermore, DgeKer could degrade feathers at 70 °C for 60 min. However, the medium became turbid with obvious softening of barbules after being treated with DgeKer-C, which might be due to C-terminal extension. In summary, a thermostable keratinase DgeKer with high efficiency degradation of feathers may have great potential in 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.

The tale of a versatile enzyme: Molecular insights into keratinase for its industrial dissemination

Keratinases are unique among proteolytic enzymes for their ability to degrade recalcitrant insoluble proteins, and they are of critical importance in keratin waste management. Over the past few decades, researchers have focused on discovering keratinase producers, as well as producing and characterizing keratinases. The application potential of keratinases has been investigated in the feed, fertilizer, leathering, detergent, cosmetic, and medical industries. However, the commercial availability of keratinases is still limited due to poor productivity and properties, such as thermostability, storage stability and resistance to organic reagents. Advances in molecular biotechnology have provided powerful tools for enhancing the production and functional properties of keratinase. This critical review systematically summarizes the application potential of keratinase, and in particular certain newly discovered catalytic capabilities. Furthermore, we provide comprehensive insight into mechanistic and molecular aspects of keratinases including analysis of gene sequences and protein structures. In addition, development and current advances in protein engineering of keratinases are summarized and discussed, revealing that the engineering of protein domains such as signal peptides and pro-peptides has become an important strategy to increase production of keratinases. Finally, prospects for further development are also proposed, indicating that advanced protein engineering technologies will lead to improved and additional commercial keratinases for various industrial applications.

Production and characterization of keratinase by Ochrobactrum intermedium for feather keratin utilization

A newly isolated bacterium producing 55.5 U/mL keratinase on feather meal minimal medium was identified as Ochrobactrum intermedium. Optimization of process parameters by one-variable-at-a-time (OVAT) approach (substrate concentration 0.5% w/v, inoculum size 5% w/v, pH 7.0, 200 rpm for 96 h at 40 °C) resulted in 2.1-fold increase in keratinase secretion (117 U/mL). Keratinase was optimally active at pH 9.0 and 40 °C and was stable at pH 9.0 and 60 °C for 120 min. Calcium ions enhanced keratinase activity (158%) significantly, while it was strongly inhibited by both PMSF and EDTA, indicating it to be a metallo-serine protease. Keratinase degraded native chicken feathers efficiently resulting in 97.9% weight loss along with release of 745.5 μg/mL soluble proteins and 4196.69 μg/mL amino acids. Feather hydrolysate generated by NKIS 1 exhibited significant anti-oxidant and free-radical scavenging activity (90.46%). The present study revealed that O. intermedium NKIS 1 has potential applications in the biodegradation of chicken feathers and the value-addition of poultry waste.

Biochemical characterization of a surfactant-stable keratinase purified from Proteus vulgaris EMB-14 grown on low-cost feather meal

OBJECTIVES

The bioaccumulation of keratinous wastes from poultry and dairy industries poses a danger of instability to the biosphere due to resistance to common proteolysis and as such, microbial- and enzyme-mediated biodegradation are discussed.

RESULTS

In submerged fermentation medium, Proteus vulgaris EMB-14 utilized and efficiently degraded feather, fur and scales by secreting exogenous keratinase. The keratinase was purified 14-fold as a monomeric 49 kDa by DEAE-Sephadex A-50 anion exchange and Sephadex G-100 size-exclusion chromatography. It exhibited optimum activity at pH 9.0 and 60 °C and was alkaline thermostable (pH 7.0-11.0), retaining 87% of initial activity after 1 h pre-incubation at 60 °C. The K_m and V_max of the keratinase with keratin azure were respectively 0.283 mg/mL and 0.241 U/mL/min. Activity of P. vulgaris keratinase was stimulated by Ca²⁺, Mg²⁺, Zn²⁺, Na⁺ and maintained in the presence of some denaturing agents, except β-mercaptoethanol while Cu²⁺ and Pb²⁺ showed competitive and non-competitive inhibition with K_i 6.5 mM and 17.5 mM, respectively.

CONCLUSION

This purified P. vulgaris keratinase could be surveyed for the biotechnological transformation of bioorganic keratinous wastes into valuable products such as soluble peptides, cosmetics and biodegradable thermoplastics.

Proteolytic bacteria isolated from agro-waste dumpsites produced keratinolytic enzymes

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Proteolytic bacteria were isolated from agro-waste dumpsites.

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

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Feather degradation generated high concentration of free thiol containing groups.

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

•

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

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

Bacillus cytotoxicus Isolated from a Pristine Natural Geothermal Area Reveals High Keratinolytic Activity

Geothermal areas are the niches of a rich microbial diversity that is not only part of the intangible patrimony of a country but also the source of many microbial species with potential biotechnological applications. Particularly, microbial species in geothermal areas in Argentina have been scarcely explored regarding their possible biotechnological uses. The purpose of this work was to explore the proteolytic and keratinolytic enzymatic potential of microorganisms that inhabit in the Domuyo geothermal area in the Neuquén Province. To this end, we did enrichment cultures from two high-temperature natural samples in mineral media only supplemented with whole chicken feathers. After the isolation and the phylogenetic and morphologic characterization of different colonies, we obtained a collection of Bacillus cytotoxicus isolates, a species with no previous report of keratinolytic activity and only reported in rehydrated meals connected with food poisoning outbreaks. Its natural habitat has been unknown up to now. We characterized the proteolytic and keratinolytic capacities of the B. cytotoxicus isolates in different conditions, which proved to be remarkably high compared with those of other similar species. Thus, our work represents the first report of the isolation as well as the keratinolytic capacity characterization of strains of B. cytotixicus obtained from a natural environment.

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

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

Recombinant expression and biochemical characterization of a novel keratinase BsKER71 from feather degrading bacterium Bacillus subtilis S1-4

Bacillus subtilis S1-4, isolated from chicken feather could efficiently degrade feathers by secreting several extracellular proteases. In order to get insight into the individual protease involved in keratin hydrolysis, a keratinase designed as BsKER71 was cloned and expressed in Bacillus subtilis WB600. In silico analysis revealed that BsKER71 protein contained a mature protein of 36.1 kDa. Further, purified BsKER71 could hydrolyze a variety of natural proteins, such as fibrous protein, collagen protein, casein, keratin and bovine serum albumin. In addition, this keratinase exhibited high enzyme activity in a wide range of pH and optimal pH of 10.0 and 9.0 in the hydrolysis of casein and keratin, respectively. Similarly, the optimal temperature was 55 °C and 50 °C for the hydrolysis of above two substrates, respectively. The hydrolytic activity was significantly inhibited by phenylmethanesulfonyl fluoride (PMSF), indicating the presence of serine residue in the active site. Moreover, ethylenediaminetetraacetic acid (EDTA) and phenanthroline moderately inhibited the hydrolytic activity. The catalytic activity was stimulated by Mg²⁺ and Ca²⁺, but greatly inhibited by Cu²⁺. Furthermore, several chemicals exhibited different effects on the hydrolysis of casein and keratin by BsKER71. These results provided a better understanding of BsKER71 from feather degrading bacterium B. subtilis S1-4.

Cloning and expression of a thermostable keratinase gene from Thermoactinomyces sp. YT06 in Escherichia coli and characterization of purified recombinant enzymes

The feather-degrading strain Thermoactinomyces sp. YT06 secretes an extracellular keratinolytic protease (KERTYT); however, the gene encoding this protease remains unknown. The kerT1 gene (1170 bp) encoding keratinase was cloned and expressed in Escherichia coli BL21(DE3). Purified recombinant keratinase (rKERTYT) was achieved at a yield of 39.16% and 65.27-fold purification with a specific activity of 1325 U/mg. It was shown that rKERTYT has many similarities to the native enzyme (KERTYT) by characterization of rKERTYT. The molecular weight of rKERTYT secreted by recombinant E. coli was approximately 28 kDa. The optimal temperature and the pH values of rKERTYT were 65 °C and 8.5, respectively, and the protein remained stable from 50 to 60 °C and pH 6-11. The keratinase was strongly inhibited by phenyl methane sulfonyl fluoride (PMSF), suggesting that it belongs to the serine protease family. It was significantly activated by Mn²⁺ and β-mercaptoethanol (β-Me). rKERTYT showed stability and retained over 80% activity with the existence of organic solvents such as acetone, methylbenzene and dimethyl sulfoxide. These findings indicated that rKERTYT will be a promising candidate for the enzymatic processing of keratinous wastes.

Identification of a novel protease from the thermophilic Anoxybacillus kamchatkensis M1V and its application as laundry detergent additive

A thermostable extracellular alkaline protease (called SAPA) was produced (4600 U/mL) by Anoxybacillus kamchatkensis M1V, purified to homogeneity, and biochemically characterized. SAPA is a monomer with a molecular mass of 28 kDa estimated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), Native-PAGE, casein-zymography, and size exclusion using high performance liquid chromatography (HPLC). The sequence of its NH₂-terminal amino-acid residues showed high homology with those of Bacillus proteases. The SAPA irreversible inhibition by diiodopropyl fluorophosphates (DFP) and phenylmethanesulfonyl fluoride (PMSF) confirmed its belonging to the serine proteases family. Optimal activity of SAPA was at pH 11 and 70 °C. The sapA gene was cloned and expressed in the extracellular fraction of E. coli. The highest sequence identity value (95%) of SAPA was obtained with peptidase S8 from Bacillus subtilis WT 168, but with 16 amino-acids of difference. The biochemical characteristics of the purified recombinant extracellular enzyme (called rSAPA) were analogous to those of native SAPA. Interestingly, rSAPA exhibit a degree of hydrolysis that were 1.24 and 2.6 than SAPB from Bacillus pumilus CBS and subtilisin A from Bacillus licheniformis, respectively. Furthermore, rSAPA showed a high detergent compatibility and an outstanding stain removal capacity compared to commercial enzymes: savinase™ 16L, type EX and alcalase™ Ultra 2.5 L.

Purification, biochemical, and molecular characterization of a novel extracellular thermostable and alkaline α-amylase from Tepidimonas fonticaldi strain HB23

The present study investigated the purification, biochemical, and molecular characterization of a novel thermostable α-amylase (TfAmy48) from Tepidimonas fonticaldi strain HB23. MALDI-TOF/MS analysis indicated that the purified enzyme is a monomer with a molecular mass of 48,138.10 Da. The results from amino-acid sequence analysis revealed high homology between the 25 NH₂-terminal residues of TfAmy48 and those of Gammaproteobacteria α-amylases. The optimum pH and temperature values for α-amylase activity were pH 8 and 80 °C, respectively. Thin-layer chromatography (TLC) analysis showed that the final hydrolyzed products of the enzyme from soluble potato starch were maltopentaose, maltose, and maltotriose, which indicate that TfAmy48 possessed an endo-acting pattern. Compared to Termamyl®300 L, TfAmy48 showed extreme stability and tolerance towards organic solvents and excellent compatibility with some commercial laundry detergents. These proprieties make TfAmy48 enzyme a potential candidate as a cleaning bioadditive in detergent composition. The Tfamy48 gene encoding TfAmy48 was cloned, sequenced, and heterologously-expressed in the extracellular fraction of Escherichia coli strain BL21(DE3)pLysS. The biochemical properties of the extracellular purified recombinant enzyme (rTfAmy48) were similar to those of native one. The highest sequence identity value (97%) was obtained with PsAmy1 α-amylase from Pseudomonas sp. strain KFCC10818, with only 16 amino-acid (aa) residues of difference.

Cloning, expression, and characterization of an alkaline protease, AprV, from Vibrio sp. DA1-1

A novel alkaline protease (named AprV) gene from Vibrio sp. DA1-1 was cloned and expressed in Escherichia coli BL21 (DE3) pLysS. The sequence analysis showed the highest homology of 68% with the characterized protease from Alkalimonas collagenimarina AC40^T. The recombinant AprV was purified with the molecular weight of 28 kDa. The optimum temperature and pH were determined to be 55 °C and 10.0, respectively. The enzyme activity was slightly enhanced by Ca²⁺, Mg²⁺, Zn²⁺, Ba²⁺, and, however, was highly inhibited by Sn²⁺ and EDTA. The AprV was stable in the presence of some surfactants and oxidizing agents, such as 1% Tween 20-80, 1% JFC-2, and 5% JFC-2. Casein was found to be the ideal substrate with specific activity of 1139 U/mg. Moreover, we found that AprV (10,000 U), together with commercial detergent, could completely remove the blood on the cotton. Furthermore, AprV also demonstrated dehairing activity on goat and bull skin. These results indicated that the alkaline protease AprV might be a potential candidate for applications in the detergent and leather industries.

Microbial Keratinases: Enzymes with Promising Biotechnological Applications

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

Biochemical characterization of a novel thermostable chitinase from Hydrogenophilus hirschii strain KB-DZ44

An extracellular acido-thermostable endo-chitinase (called ChiA-Hh59) from thermophilic Hydrogenophilus hirschii strain KB-DZ44, was purified and characterized. The maximum chitinase activity recorded after 36-h of incubation at 60°C was 3000U/ml. Pure enzyme was obtained after heat and acidic treatment, precipitation by ammonium sulphate and acetone, respectively, followed by sequential column chromatographies on Sephacryl S-200 and Mono Q-Sepharose. Based on Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS) analysis, the purified enzyme is a monomer with a molecular mass of 59103.12-Da. The 22 residue NH₂-terminal sequence of the enzyme showed high homology with family-18 bacterial chitinases. The optimum pH and temperature values for chitinase activity were pH 5.0 and 85°C, respectively. The pure enzyme was completely inhibited by p-chloromercuribenzoic acid (p-CMB) and N-ethylmaleimide (NEM). The obtained results suggest that ChiA-Hh59 might be an endo-chitinase. The studied chitinase exhibited high activity towards colloidal chitin, chitin azure, glycol chitin, while it did not hydrolyse chitibiose and amylose. Its K_m and k_cat values were 0.298mg colloidal chitin/ml and 14400s^-1, respectively. Its catalytic efficiency was higher than those of chitodextrinase and ChiA-65. Additionally, Thin-layer chromatography (TLC) analysis from chitin-oligosaccharides showed that ChiA-Hh59 acted as an endo-splitting enzyme. In conclusion, this chitinase may have great potential for the enzymatic degradation of chitin.

Development of a keratinase activity assay using recombinant chicken feather keratin substrates

Poultry feathers consist mainly of the protein keratin, which is rich in β-pleated sheets and consequently resistant to proteolysis. Although many keratinases have been identified, the reasons for their substrate specificity towards β-keratin remain unclear due to difficulties in preparing a soluble feather keratin substrate for use in activity assays. In the present study, we overexpressed Gallus gallus chromosomes 2 and 27 β-keratin-encoding genes in Escherichia coli, purified denatured recombinant proteins by Ni²⁺ affinity chromatography, and refolded by stepwise dialysis to yield soluble keratins. To assess the keratinolytic activity, we compared the proteolytic activity of crude extracts from the feather- degrading bacterium Fervidobacterium islandicum AW-1 with proteinase K, trypsin, and papain using purified recombinant keratin and casein as substrates. All tested proteases showed strong proteolytic activities for casein, whereas only F. islandicum AW-1 crude extracts and proteinase K exhibited pronounced keratinolytic activity for the recombinant keratin. Moreover, LC-MS/MS analysis of keratin hydrolysates allowed us to predict the P1 sites of keratinolytic enzymes in the F. islandicum AW-1 extracts, thereby qualifying and quantifying the extent of keratinolysis. The soluble keratin-based assay has clear therapeutic and industrial potential for the development of a high-throughput screening system for proteases hydrolyzing disease-related protein aggregates, as well as mechanically resilient keratin-based polymers.

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

Dehairing is a high pollution process in leather industry. Conventionally, the lime-sulfide mediated chemical process for dehairing would lead to the discharge of pollutants and corrosion of industrial equipment. Concerning these problems, keratinase has become a promising candidate for dehairing process in recent years. In this study, a keratinase-producing bacterium was isolated from sheepfold soil and identified as Brevibacillus parabrevis CGMCC 10798 based on the biochemical characteristics and molecular identification. The keratinase was purified to electrophoretic homogeneity with 17.19% of recovery, 13.18 folds of purification and an estimated molecular weight of 28kDa. The enzyme exhibited high keratinase activity and no collagenase activity. Besides, the keratinase showed optimal activity at 60°C and pH 8.0. The enzyme activity could be significantly increased in the presence of Na⁺ and Ca²⁺. And it was inhibited by EDTA, and PMSF, which indicated that the keratinase belongs to serine-metallo protease. The enzyme could remain stable in the presence of surfactants. Especially, 5mM Tween 40 and Triton 100 could improve the activity by 11% and 30%, respectively. Moreover, B. parabrevis keratinase could completely dehair goat wool within 7h, which indicated its application potential in leather industry.

Effect of Substrate on Identification of Microbial Communities in Poultry Carcass Composting and Microorganisms Associated with Poultry Carcass Decomposition

Three composting systems, which consisted of different ratios of chicken manure, sawdust, and poultry carcasses, were used to investigate the effect of substrate on the identification of microbial communities and microorganisms associated with poultry carcass decomposition by characterizing the microbial communities and physicochemical parameters. The physicochemical and Miseq Illumina sequencing results showed the composition of substrate had a significant effect on the identification and metabolic capabilities of microbial communities in decomposting process. Poultry carcasses might be the potential driver for the identification of bacterial communities in poultry carcass composting, whereas the initial C/N ratio may mainly contribute to the diversity of fungal communities and the similar dominant microbial communities in treatments. Poultry carcasses and initial C/N ratio could respectively affect the composition and abundance of microorganisms associated with the decomposition of poultry carcasses. Understanding the potential composting driver could allow development of an efficient carcass degradation system.

Biochemical and molecular characterization of new keratinoytic protease from Actinomadura viridilutea DZ50

A new extracellular thermostable keratinolytic protease, designated KERDZ, was purified and characterized from a thermophilic actinomycetes Actinomadura viridilutea DZ50 isolated from Algerian fishing port. The isolate exhibited high keratinase production when grown in chicken-feather meal media (18,000U/ml) after 96-h of incubation at 45°C. The enzyme was purified by ammonium sulfate precipitation (35-55%)-dialysis and heat treatment (30min at 75°C) followed by UNO S-1 FPLC cation exchange chromatography and size exclusion HPLC column. The biochemical characterizations carried on include physico-chemical determination and spectroscopic analysis. The MALDI-TOF/MS analysis revealed that the purified enzyme was a monomer with a molecular mass of 19536.10-Da. The sequence of the 25 N-terminal residues of KERDZ showed high homology with those of actinomycetes keratinases. Optimal activity was achieved at pH 11 and 80°C. KERDZ was completely inhibited by PMSF and DFP suggested its belonging to the serine keratinase family. KERDZ displayed higher levels of hydrolysis and catalytic efficiency than bacterial keratinases (KERAK-29, Actinase E, and KERAB) and subtilisins (subtilisin Carlsberg and subtilisin Novo). The kerDZ gene encoding KERDZ was isolated and its DNA sequence was determined. These properties make KERDZ a potential, promising and eco-friendly alternative to the conventional chemicals used for industrial applications.