Keratin Degradation by Penicillium purpurogenum and Aspergillus niger Isolated from Nigerian Soils Polluted with Tannery Wastes
Background: Keratinophilic fungi are a group of fungi that colonize various keratinous substrates and degrade them to components of low molecular weight. Keratinized tissues include feathers, beaks of birds, horns, hooves, skins, hair, fur, wool, nails and claws of animals. Tannery soils are very rich in keratinous materials such as fur, wool and hair that are by-products of the tanning industry where hides and skins are processed. Keratinase producing fungi, Aspergillus niger and Penicillium purpurogenum were isolated from soils containing tannery wastes in Jos, Plateau State Nigeria.
Materials and Methods: Skim milk casein agar was employed to assay for extra cellular protease as an indication for keratinase production. The species had maximum proteolytic and keratinase activities in a Submerged Fermentation (SmF) using liquid basal medium supplemented with skim milk, chicken feathers and human hair as carbon and nitrogen sources. Effects of incubation temperature on protease and keratinase enzyme activity were also determined.
Results: The Spectrophotometric assay of the proteolytic and keratinolytic activity showed that P. purpurogenum had the highest activity (13.5 U/ml) on chicken feathers. This was followed by human hair with activity of 12 U/ml. The least activity of 11.9 U/ml was observed in skim milk medium. Similar results were recorded for A. niger with highest activity of 11.8 U/ml on chicken feathers. This was followed by human hair with activity of 10.6 U/ml while skim milk agar had the least activity of 10.0 U/ml. It was observed that incubation temperature had effects on the enzyme activity, with an optimum temperature of 37°C for both protease and keratinase.
Conclusion: These non-dermatophytic keratinolytic fungi may have potential use in biotechnological processes involving keratin hydrolysis. The results of this work reiterated that keratinolytic activity is relatively widespread among common fungi and may have an important role in keratin degradation in the natural environment. P. purpurogenum and A. niger bio-degraded skim milk casein, human hair and chicken feather in Submerged Fermentation (SmF). They had the greatest activity on chicken feathers indicating that they could be employed in waste and environmental pollution management. In Nigeria, poultry feathers, animal hair and other keratin sources including tannery wastes do not find suitable applications. Practical use of keratinase producing microorganisms such as the ones used in this study is being explored in applied microbiology where there is great need for active degraders for the management of keratin containing wastes.
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