Study of Bacillus sp. culture conditions to promote production of unhairing proteases

ABSTRACT

The substitution of chemical depilatory agents in the leather industry by proteolytic enzymes produced by Bacillus species has an important economical and environmental impact. In previous assays, a Bacillus sp. showing a promising depilatory activity was isolated. In this paper, a culture medium that stimulated the synthesis and segregation of depilatory proteases, was selected. The influence of pH, oxygen supply rate (KLaC*), and inoculum age was evaluated on cell growth and protease production. Assays were carried out in lab bioreactors (1.2-1.4 l) at 37 degrees C. Five different media that differed in carbon and nitrogen sources were tested. pH ranged from 4.0 to 8.5. KLaC* varied between 40 and 470 mmol/lh. The best medium culture for protease production contained: nutrient broth (Britania) 8 g/l, yeast extract (Britania) 3 g/l, and mineral salts. Protease production was more effective at pH of 6.7, KLaC* of 360 mmol/lh, and inoculum age of 12 hours. These experimental conditions led to the following results: maximum proteolytic activity 2700 U/ml, overall volumetric protease productivity 300 u/ml-h, average specific growth rate 0.62 h-1, and average specific protease production rate 2.50 x 10(5) U/gh.