Development of Bacillus subtilis self-inducible expression system for keratinase production using piggery wastewater

•Piggery wastewater (PW) could be used as potent nutrient source for enzyme synthesis.•The utilization of PW supplemented with LB medium favoured the keratinase production.•Highest yield of 968 U/mL was achieved with the manP-deleted PT513(DMT1-mKerP). Piggery wastewater (PW) from pig farms generally consists of a high concentration of organic components which is recognized as one of the main causes of water pollution. PW could be a potential nutrient source in bacterial fermentation for cells growth and valuable biocompounds synthesis, thus minimizing the generation of wastewater effluent. Keratinase is a proteolytic enzyme that can effectively degrade keratin into peptides or amino acids, which has been extensively applied in the animal feed, fertilizers, detergents, and leather industries. This study was aimed to establish two self-inducible T7 expression systems in Bacillus subtilis for the expression of keratinase and investigate the feasibility of PW as a nutrient source for the keratinase production by recombinant B. subtilis. The manP-deleted PT513(DMT1-mKerP) bacterial strain was found to facilitate keratinase expression in medium with only PW and 50L50W (50% LB and 50% PW) medium through the T7 system regulated by manP promoter whereby the yield of 501 ± 34 U/mL and 968 ± 74 U/mL, respectively were achieved. The findings demonstrated that the self-inducible T7 expression strain PT513(DMT1-mKerP) was favorable for keratinase production with the utilization of wastewater as a nutrient source in the cultivation medium.