Comprehensive insights into microbial keratinases and their implication in various biotechnological and industrial sectors: A review.

The world’s increasing population and shortage of food and feed is creating an urgently for us to look for new protein sources from waste products like keratinous waste. Poor management of these wastes has made them one of the major recalcitrant pollutants in nature. Microbial keratinases offers an economic and eco-friendly alternative for degrading and recycling keratinous waste into valuable byproducts. Diverse groups of microorganisms viz., bacteria, fungi and actinomycetes have the ability to degrade recalcitrant keratin by producing keratinase enzyme. Microbial keratinases exhibits great diversity in its biochemical properties with respect to activity and stability in various pH and temperature ranges as well as in the range of recalcitrant proteins it degrades like those present in feathers, hairs, nails, hooves etc. Owing to diverse properties and multifarious biotechnological implications, keratinases can be considered as promising biocatalysts for preparation of animal nutrients, protein supplements, leather processing, fiber modification, detergent formulation, feather meal processing for feed and fertilizer, the pharmaceutical, cosmetic and biomedical industries, and waste management. This review article presents an overview of keratin structure and composition, mechanism of microbial keratinolysis, diversity of keratinolytic microorganisms, and their potential applications in various fields.

Versatility and commercial status of microbial keratinases: a review

Production and characterization of a novel thermo- and detergent stable keratinase from Bacillus sp. NKSP-7 with perceptible applications in leather processing and laundry industries

Microbial and enzymatic degradation of keratin waste is more preferred over various conventional approaches which are costly and not environmentally suitable. Diverse niches are auspicious for the discovery of new microorganisms. To discover novel keratinolytic bacteria, 60 isolates from different poultry dumping sites were initially screened, and among these found a potent keratinolytic isolate (NKSP-7) that displayed higher feather-degrading ability. The selected isolate was identified as Bacillus sp. NKSP-7 based on 16S rDNA sequencing as well as physiochemical and morphological characteristics. The strain NKSP-7 showed complete hydrolysis of native chicken feathers (10 g/L) in nutrient medium after 24 h of incubation at 37 °C under agitation (150 rev/min) and produced thermostable extracellular keratinase. The crude enzyme displayed maximal keratinolytic activity (34.7 U/mL) in phosphate buffer of pH 7.0, and at 60 °C using keratin azure as a substrate. Keratinolytic enzyme showed stability at 20–65 °C for 4 h over the pH range of 5.5–8.0. No obvious inhibitory influence was perceived by cations, organic solvents, EDTA, and detergents. Whereas, enzyme activity was enhanced by adding β-mercaptoethanol, Na+, Cd2+, and Mn2+. All these notable features of keratinase make it a promising candidate for various industrial applications especially for dehairing process in leather industry, bioconversion of poultry waste, and in detergents formulations.

Keratinolytic enzyme-mediated biodegradation of recalcitrant poultry feathers waste by newly isolated Bacillus sp. NKSP-7 under submerged fermentation.

Background: The enzymatic degradation of keratin-rich wastes by a keratinolytic microorganism is a preferable and eco-friendly biotechnological alternative for the valorization of these compounds. Despite their recalcitrant behavior, hydrolysis of these wastes can be efficiently done by microbial proteolytic enzyme known as keratinase. Objective: In the present study, a potent keratinolytic bacterial strain with a great potential of feathers’ degradation was isolated and identified by 16S rDNA sequencing as Bacillus sp. NDS-10. Results: After optimization, high-yield of extracellular keratinase (92 U mL−1) and bioconversion of feathers (97%) were achieved in M9 medium (pH 7.0) containing 0.8% (w/v) native chicken feathers after 20 h incubation at 45 °C. The crude keratinase exhibited maximal activity at pH 7.0–8.0 (Tris-Cl buffer) and 65 °C; and showed great stability over a range of pH (6.0–10.0) and temperature (20-60°C) for 6 h. No inhibitory influence was observed with various chemical modulators, commercial detergents and salt but phenylmethanesulfonyl fluoride (PMSF) completely repressed the keratinolytic activity of enzyme. The enzyme effectively dehaired goat hide after 6 h without any damage and completely removed the blood-stain after 5 min incubation. Conclusion: These favorable features indicated that this keratinolytic enzyme seems to be an efficient and eco-friendly candidate for keratin-waste management, detergents formulations and hide-depilation application.

Keratinolytic Enzyme from a Thermotolerant Isolate Bacillus sp. NDS-10: An Efficient Green Biocatalyst for Poultry Waste Management, Laundry and Hide-dehairing Applications

A large amount of feather waste is generated from the poultry industry. This waste containing a considerable amount of keratin can be utilized by microorganisms thus leading to its environmentally safe disposal. The objective of the study was to isolate and identify a feather degrading bacterium from poultry farm soil, optimize the cultural conditions and partial purification of keratinase enzyme using ammonium sulphate precipitation, followed by exploring the applications. The study was carried out by collecting soil samples, enrichment using an appropriate enrichment medium, followed by screening, identification and then optimizing cultural conditions. The isolated keratinolytic bacterium carried out complete degradation of the feather waste within 4 weeks and was found to be of Bacillus sp. by biochemical identification. The bacterium presented optimum growth at pH 6.8 and a temperature of 37 oC. The keratinase enzyme activity was found to be 8.80U/ml/min for isolate P and 13.60U/ml/min for isolate W. The study shows the potential of the feather degrading isolate to carry out environmentally safe disposal of poultry waste and also to produce amino acids from a cheap raw material.

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G. M. Bilakhia

Papers

Screening and Characterisation of Keratinase Enzyme Obtained From Keratin Degrading Microorganism Isolated From Sanjan Poultry Waste Dumping Soil