Production of alkaline protease and larvicidal biopesticides by an Egyptian Bacillus sphaericus isolate

Abstract

One strain, isolated from Egyptian soil, was identified as

Bacillus sphaericus with powerful larvicidal toxicity against C. pipiens and extra-cellular production of alkaline protease (AP) in the growth medium. The pH adjustment of the growth medium between 6.0 and 7.5 resulted in the highest AP activity, peaking at pH 6.5. AP crude preparations exhibited optimum activity at pH 10 and at temperature range of 65 - 70ºC. Interestingly, the highest AP activity was observed with 3% fodder yeast, as the sole component of the medium. Moreover, optimal AP yield was attained by using strong aeration at 9:1 (air : medium) ratio. Similarly, the highest AP enzyme level was consistently achieved 3-day after aerobic growth in shake flasks at 30ºC, without significant decrease in AP yield upon extended incubation periods up to 6 days. Notably, maximum proteolytic activity was achieved with casein as a substrate followed by skim milk, gelatin and bovine serum albumin. The crude AP enzyme activity exhibited quasi-linear response with enzyme concentrations up to 0.25 mg ml-1. The isolated B. sphaericus might be employed for the economic production of important products such as biopesticides and proteolytic enzymes.