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

Microbial keratinases: An overview of biochemical characterization and its eco-friendly approach for industrial applications

Keratins are insoluble, fibrous, and structural proteins that are present in the epidermis and its appendages and these include feather, hair, wool, nail, hoof, and horns. Keratins adhere epidermal cells to one another and provide protection on the skin. They are structurally stabilized by their tightly packed peptide chains and the existence of several cross-linkages by disulphide bonds, hydrogen bonding, and hydrophobic interactions. Keratin-containing materials are generated abundantly as by-products of agro-industrial processing and constitute nuisance in the environment as a result of their recalcitrance to degradation by regular proteolytic enzymes like pepsin, trypsin, and papain. The traditional physical and chemical techniques for their treatment are expensive, energy consuming, can damage some essential amino acids, and non-environmentally benign. However, degradation by a variety of microorganisms had proven to be a viable alternative means of keratin treatment. A vast variety of bacteria, fungi, and actinomycetes have been recognized as keratin degraders. They degrade keratins mainly with their keratinases, which sometimes act synergistically with other enzymes like disulfide reductases and cysteine dioxygenase for effective degradation of keratins. The microbial keratinases hydrolyze keratins into soluble proteins, peptides, and amino acids. They are utility enzymes with very diverse biotechnological applications. Biodegradation of keratin-rich wastes by microorganisms is therefore an efficient, cheap, and eco-friendly method of waste management and production of products of high biotechnological value. The present review examines the trends in the role of microorganisms for the biotechnological treatment of keratin-rich wastes.

Degradation of Keratin Biomass by Different Microorganisms

1. The main aim of this work is to develop a robust method to generate a microbial mixture which can successfully degrade poultry feathers to overcome environmental problems. 2. Four different alkaliphilic microbes were isolated and shown to degrade poultry feathers. 3. Two of the isolates were phylogenetically identified as Lysinibacillus and the others were identified as Nocardiopsis and Micrococcus. 4. The best microbial co-culture for white and black feather degradation was optimised for pH, temperature and relative population of the isolates to achieve almost 96% of degradation compared with a maximum of 31% when applying each isolate individually. 5. The maximum activity of keratinase was estimated to be 1.5 U/ml after 3 d for white feathers and 0.6 U/ml after 4 d for black feathers in a basal medium containing feather as the main carbon source. Additionally, non-denaturing polyacrylamide gel electrophoresis showed 4 and 3 protease activity bands for white and black feather, respectively. 6. This study provides a robust method to develop potential new mixtures of microorganisms that are able to degrade both white and black feathers by applying a Central Composite Design.

Bioprocess enhancement of feather degradation using alkaliphilic microbial mixture.

Isolation, Identification, Characterisation Of Bacterial Species From Keratinase Producing Microorganism

Aims: To isolate and identify feather degrading bacteria from soils collected from the feather dumping site. Study Design: Isolation and preliminary identification of bacterial isolates with keratinolytic potentials. Place and Duration of Study: Mudalawal poultry processing site, Bauchi state, Nigeria, between January 2014 to October, 2014. Methods: Soil samples from feather dumping sites were screened for bacterial growth. The Original Research Article Iruolaje et al.; JABB, 5(2): 1-9, 2016; Article no.JABB.22082 2 isolated bacteria were identified based on their morphological and biochemical characteristics and were tested for their ability to degrade whole intact feather and powdered feather samples. Results: The results showed that three (3) of the isolates belonged to the genus Bacillus which include; Bacillus licheniformis, Bacillus subtilis and Bacillus cereus, while one isolate is a Gramnegative rod, Serratia marcencens. Although B. licheniformis demonstrated higher feather degrading ability but with no statistical difference from other isolates in degrading both powdered and intact whole feathers samples. Synergy among the isolates to degrade powdered feather showed no statistical difference (p=0.317). Also, synergy among all the isolates resulted in degradation of intact feather significantly higher than that of S. marcescens, but not significantly different from those of B. licheniformis (p=0.389), B. subtilis (p=0.096) and B. cereus (p=0.096). Moreover, the keratinolytic ability of the isolates on intact whole feather was time dependent. It was also observed that the rate of degradation of powder feather samples was significantly higher than the rate of degradation of intact whole feather by all the isolates (p=0.026). Conclusion: These isolates are therefore promising organisms for the management of chicken feather waste through biotechnological processes.

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Papers

Isolation and Identification of Keratinolytic Bacteria that Exhibit Feather-degrading Potentials