Resumo

Keratin is an insoluble and a hard to degrade protein. Its decomposition in environment is effected by keratinases and disulfide reductases. Keratinases are well studied and have applications like detergent additive and in leather industry. Some microorganisms produce keratinases, specially the genera Bacillus. Bacillus subtilis S14 produces the keratinase KerS14, that has a strong potential in tannery since it is able to hydrolyze keratin without damaging collagen. The role of disulfide reductase in keratin degradation is still poor understood. The aims of the present work are select growth conditions for keratinases and disulfide reductase production in submerged fermentation. Culture medium composition was 1.5% feather meal and 1.05% CaCl₂ at 37 °C. The 4 liters tank was aerated at 1 vvm, but two agitations values were selected: 200 (low level) and 600 rpm (high level). For inoculum, 40 mL of 12 hours B. subtilis S14 grown in LB medium culture was utilized. The period of fermentation was 48 hours. Samples were collected and analyzed for keratinase, disulfide reductase, soluble protein and thiol formation. The pH and oxygen dissolved (pO₂) were monitored. Data show that during fermentation, pH media increases from 5.5 to 7-7.5. The pO₂ dissolved in low level agitation decreases to 0% in 6 hours after inoculum. Instead, in high level agitation, pO₂ decreases just to 90% after 6 hours and remains in this level during all fermentation. Thiol formation and soluble protein increase during fermentation, suggest feather meal degradation by both enzymatic activities. Disulfide reductase activity was observed in both fermentations with the highest activity (0.125 enzymatic units.mL^-1.h^-1) at 48 h. By the other hand, the keratinase production was highest in high level agitation, 7.2 enzymatic units.mL ^-1.h^-1 at 33 h, instead 200 rpm 5 enzymatic units.mL^-1.h^-1 at 26 h. These data concluding that keratinases and disulfide reductase are produced by B. subtilis S14 to degrade keratin in bioreactor.