First evidence of keratinolytic activity in Simplicillium aogashimaense isolated from wool-pellet-amended soil

Keratin-rich waste such as wool and feather wastes are generated in large quantities worldwide and remain difficult to valorize due to the structural resilience of keratin, that is reinforced by disulfide bonds. Microbial degradation offers a sustainable approach for converting these wastes into value-added products. In this study, keratin-degrading fungi were isolated from garden soils amended with wool pellets used as organic fertilizer. Three fungal strains showing keratinolytic activity were selected based on halo formation on keratin-containing agar media. Among them, Simplicillium aogashimaense was chosen for detailed characterization due to its non-pathogenic status, limited representation in the literature, and the absence of previously reported proteolytic or keratinolytic activity.

Feather meal degradation by S. aogashimaense was investigated during 12 days of submerged cultivation. The strain demonstrated strong keratinolytic potential, achieving up to 80% feather meal mass reduction. Biochemical analysis of the resulting hydrolysates, including protease activity, elemental composition, amino acid profiles, ammonium and sulfur concentrations, pH dynamics, and overall biochemical profile, revealed a multiphasic degradation pattern. The initial phase (days 1-3) was characterized by rapid feather breakdown, elevated protease activity, ammonium release, and preferential liberation of surface-accessible amino acids, indicating efficient enzymatic attack on exposed keratin domains. The intermediate phase (days 4-6) during which general protease activity declines along with the fungal biomass. This period is likely to correspond to a shift from feather degradation to assimilation and intracellular metabolism. During the final phase (days 7-12), measured parameters stabilized, consistent with maximal substrate degradation and subsequent assimilation of soluble hydrolysis products by the fungus.

This study provides the first evidence that S. aogashimaense exhibits keratin-degrading capability, identifying it as a previously unrecognized keratinolytic fungal species. These findings broaden current understanding of fungal keratin degradation and highlight the potential of S. aogashimaense for sustainable bioconversion of feather waste and other keratin-rich residues. Further optimization and mechanistic investigation of its enzymatic system may support future biotechnological applications in waste valorization.