Fungal xylanases; Characterization and Possible Biotechnological Application

Abstract

Xylanases possess tremendous importance in various industrial and agricultural sectors. Hence, the present study was conducted to explore xylanases from indigenous fungal strains, and their biotechnological applications. After initial screening of fungal strains for xylanase production and characterization of xylanases at different temperatures and pH, a total of 3 strains including A. oryzae DK5, A. niger MS34 and A. tubingensis MS80 were selected for further studies, these strains produced comparatively higher enzyme titers and showed the optimum activity at relatively high temperature i.e. 65°C. The studies on cultural conditions for xylanase production suggested the mesophilic nature of fungal strains; the growth medium of pH 8 depicted the optimum xylanase levels. Furthermore, A. oryzae DK5 and A. tubingensis MS80 possessed highest xylanase production at the substrate (beechwood xylan) conc. of 0.5% (w/v) whereas A. niger MS34 yielded the maximum titers in presence of 1% beechwood xylan. Among different carbon and nitrogen sources tested for xylanase production, the strains showed higher xylanase levels in presence of birchwood xylan, peptone and ammonium sulfate. Moreover, the data obtained from growth and xylanase production kinetic studies indicated that A. oryzae DK5 yielded more promising results. Keeping in view the importance of stability of enzymes, the crude xylanases were also studied for their stability at different temperatures and pH, and in presence of various metallic ions, EDTA, urea and organic solvents. The results showed lower enzyme stability at higher temperatures and alkaline conditions. The xylanase preparations were more stable in presence of many metallic-ions and urea. Moreover, EDTA and some of studied organic solvents increased the xylanase stability of A. oryzae DK5 and A. niger MS34 but decreased the stability of A. tubingensis MS80. xiv In order to find cheaper sources for xylanase production, studies were conducted to screen various natural conventional and novel (the halophytic plants) sources as substrates for xylanase production which suggested that the halophytic plants particularly, Phragmites karka and Typha domingensis could be used as efficient substrates for xylanase production. The crude xylanases were also checked for their potential in bioscouring of fabric which showed promising results when enzymes, were applied to fabric in combination with SDS. However, the whiteness of fabric was reduced. Also, the scanning microscopy of bioscoured fabrics depicted rough surfaces upon fabric treatment with enzyme preparation with A. oryzae DK5. However, fabric exposure to enzyme preparation from A. niger MS34 and A. tubingensis MS80 showed smooth fabric surfaces.