Inhibition of proteases during fermentation improves xylanase production by alkali tolerantAspergillus fumigatus ARl

Abstract

An alkali-tolerantAspergillus fumigatus ARl produced a high level of xylanase (228 U/ml) at 42 h of submerged fermentation at pH 9.0. During later culture periods, xylanase activity declined considerably and reached 45 U/ml at 90 h. This trend is because of proteolytic degradation of xylanases sinceA. fumigatus co-produced multiple proteases with high activity (120–159 U/ml) during submerged fermentation. Xylanase and protease were found to be active over a wide range of pH from 5.5 to 9.0. In contrast, protease lost its activity completely in the presence of CuSO₄ (25 mM) while xylanase remained active. The selective inhibition of proteases by the addition of CuSO₄ to the culture medium prevented proteolytic degradation of xylanase and improved the production of xylanase by 3-fold.