Bacillus thuringiensis

whey fermentation

protease production

single-cell protein

Biological and chemical treatment

Reuse of wastewaters

Utilization of whey as a fermentation substrate offers an opportunity to produce valuable products. The current work was carried out in order to evaluate the capability of bacteria isolated from mangrove rhizosphere soil in Jazan (Kingdom of Saudi Arabia) for the production of extracellular protease using fresh whey as a substrate. The bacterial isolate with the maximum proteolytic activity was identified by biochemical and 16S rDNA techniques as Bacillus thuringiensis. The factors affecting bacterial growth and protease production were investigated. The maximum protease production was achieved with minimal medium supplemented with 50% whey, 1% skim milk, 10% NaCl, and 1% CaCl2 at pH 7.0 and temperature 37ºC. In a fermentation experiment, B. thuringiensis utilized whey as a substrate for the production of extracellular protease with a high specific activity. The protease was precipitated using ammonium sulfate, followed by dialysis to yield 9.7-fold purification with 70.8% recovery. After fermentation, there was a remarkable reduction of BOD, COD, and COD/BOD ratio. A high yield of biomass with a promising protein level was obtained. In conclusion, B. thuringiensis demonstrated a high capability for extracellular protease and single cell protein production using whey as a costeffective medium that could minimize environmental pollution.