Xylanase production by a newly isolated Aspergillus foetidus strain and its characterization

Xylanase production by a newly isolated Aspergillus foetidus MTCC 4898 was studied using submerged fermentation under shaking. The maximum xylanase yield (210 U/ml) was obtained with negligible cellulase activity at 30 °C using 1% birchwood xylan as substrate in 3 days of cultivation. The strain was able to produce extracellular xylanases on birchwood xylan as well as on cellulose rich substrates also with very poor cellulase production (<0.1 FPU/ml). The partially purified enzyme recovered by ammonium sulphate fractionation showed maximum activity at 50 °C and at pH 5.3. The enzyme was highly stable at 40 °C but retained 36% of its activity at 50 °C after 3 h. The presence of KCl, CaCl2, glycerol, xylan and trehalose significantly improved thermostability at 50 and 60 °C. Zymogram analysis indicated three isoenzymes. The enzyme preparation was completely stable at freezing temperature for up to 6 months and reasonably stable at refrigeration temperatures for more than 2 weeks.