Simultaneous production of biopesticide and alkaline proteases by Bacillus thuringiensis using sewage sludge as a raw material

Abstract

The simultaneous production of Bacillus thuringiensis (Bt) based biopesticide and proteases was studied using synthetic medium and wastewater sludge as a raw material. The studies were conducted in shake flask and computer controlled 15-L capacity fermentors. Measuring viable cell and spore counts, entomotoxicity and protease activity monitored the progress of the biopesticide production process. A higher viable cell count and spore count was observed in synthetic Soya medium, however, higher entomotoxicity and protease activity were observed in wastewater sludge medium. Thus, the wastewater sludge is a better raw material than commercial Soya medium for the biopesticides and enzyme production. The maximum entomotoxicity and protease activity observed in the fermentor was 9,332 IU/μL and 4.58 IU/mL, respectively. The proteases produced by Bt were also characterised. Two types of proteases were detected; neutral proteases with pH optimum 7.0 and alkaline proteases with pH optimum 10-11. Further, two types of alkaline proteases were detected; one having a pH and temperature optimum at 10 and 50°C while the other at 11 and 70°C. The protease thermal stability was found to increase in the presence of CaCl2, indicating the proteases were metalloproteases.