Purification and biochemical characterization of two keratinases from Bacillus amyloliquefaciens S13 isolated from marine brown alga Zonaria tournefortii with potential keratin-biodegradation and hide-unhairing activities

Abstract

The current paper reports the purification and biochemical characterization of two extracellular keratinolytic enzymes, with moderate elastolytic activity, from Bacillus amyloliquefaciens strain S13 newly isolated from the brown alga Zonaria tournefortii. The enzymes were purified to homogeneity by precipitation with (NH4)2SO4-dialysis, followed by size exclusion HPLC column, and submitted to biochemical characterization assays. The findings revealed that the pure enzymes designated KERZT-A and B were monomers with molecular masses of 28 and 47 kDa, respectively. Their identified NH2-terminal amino acid displayed high homologies with those of Bacillus keratinases. While KERZT-A was optimally active at pH 6.5 and 50 °C, KERZT-B showed optimum activity at pH 8 and 60 °C. Both enzymes were completely inhibited by phenylmethanesulfonyl fluoride (PMSF) and diiodopropyl fluorophosphates (DFP), which suggests their belonging to the serine keratinases family. Interestingly, KERZT-A displayed higher levels of hydrolysis, substrate specificity, and catalytic efficiency than KERUS from Brevibacillus brevis strain US575, NUE 12 MG (commercial enzyme), and KERZT-B unhairing keratinases. Above all, the findings indicated that KERZT-A and B enzymes seems to be an effective and an eco-friendly alternative to the conventional chemicals used for the feather keratin-biodegradation and for the unhairing of hides or skins in the leather processing industry.