Degradation of feather waste by Aspergillus niger keratinases: Comparison of submerged and solid-state fermentation

The isolation of native and/or the production of genetically modified enzyme-producing microorganisms may have substantial impacts on industrial processes. In this work twenty-eight Aspergillus niger mutants were screened for peptidases and keratinases production on a basal medium containing chicken feathers (1%). Four strains were selected after preliminary assays: 3T5B8, 9D40, 9D80, and 11D40. The keratinase production was higher when the A. niger strains were cultivated in a solid-state condition rather than a submerged condition: the keratinolytic activity of 3T5B8 strain was 7 times greater when cultivated by solid-state fermentation (SSF). A. niger 3T5B8 had the highest keratinase activity (172.7 U/ml) after seven days at pH 5.0 from solid-state fermentation, whereas the lowest activity was given by A. niger 9D40 after four days (21.3 U/ml) from submerged fermentation. Zymography of culture supernatant showed multiple bands migrating at 40-130, 14-130, displaying activity towards keratin and gelatin substrates, respectively. This is the first study to report production of high molecular mass peptidases using a feather-degrading Aspergillus. Peptidases from strains 3T5B8, 9D40, 9D80, and 11D40 were inhibited by PMSF, except the approximately 40-kDa peptidase, which was inhibited by phenanthroline, indicating the presence of serine and metallopeptidases. The results therefore suggest that the isolates are promising keratinase producers for biotechnological purposes.