Fermentation production of keratinase from Bacillus licheniformis PWD-1 and a recombinant B. subtilis FDB-29

Fermentation scale-up was studied for the production of keratinase by Bacillus licheniformis PWD-1, the parent strain, and B. subtilis FDB-29, a recombinant strain. In both strains, keratinase was induced by proteinaceous media, and repressed by carbohydrates. A seed culture of B. licheniformis PWD-1 at early age, 6-10 h, is crucial to keratinase production during fermentation, but B. subtilis FDB-29 is insensitive to the seed culture age. During the batch fermentation by both strains, the pH changed from 7.0 to 8.5 while the keratinase activity and productivity stayed at high levels. Control of pH, therefore, is not necessary. The temperature for maximum keratinase production is 37 degrees C for both strains, though B. licheniformis is thermophilic and grows best at 50 degrees C. Optimal levels of dissolved oxygen are 10% and 20% for B. licheniformis and B. subtilis respectively. A scale-up procedure using constant temperature at 37 degrees C was adopted for B. subtilis. On the other hand, a temperature-shift procedure by which an 8-h fermentation at 50 degrees C for growth followed by a shift to 37 degrees C for enzyme production was used for B. licheniformis to shorten the fermentation time and increase enzyme productivity. Production of keratinase by B. licheniformis increased by ten-fold following this new procedure. After respective optimization of fermentation conditions, keratinase production by B. licheniformis PWD-1 is approximately 40% higher than that by B. subtilis FDB-29.