Study of the intracellular xylanolytic activity of the phytopathogenic fungus Sporisorium reilianum

The present study demonstrates that Sporisorium reilianum, a phytopathogenic fungus of corn, produces intracellular xylanolytic activity during submerged fermentation. Production reached its highest levels in a medium containing glucose, corn hemicellulose and yeast extract. An intracellular xylanase was purified by a process that included precipitation with ammonium sulfate, ion exchange chromatography and gel filtration. Optimal pH and temperature values were 5.0 and 60 °C, respectively. The enzyme showed activity through a broad pH range. The molecular weights of pure xylanase were 36 and 37 kDa, determined by SDS PAGE and gel filtration, respectively. K_m and V_max were 0.160 mg/mL and 1.564 μmol/min/mg, respectively, on a substrate of birchwood xylan. SDS, EDTA, β-Mercaptoethanol, Tween 80, Triton and Mn²⁺ and Ca²⁺ strongly inhibited activity. The purified enzyme hydrolyzed xylan, releasing xylotriose and xylobiose. Sequence protein analysis showed 95% similarity with the theoretical protein encoded by the sr14403 gene of S. reilianum, which encodes a putative endo-β-1,4-xylanase. The enzyme is an isoform of the extracellular xylanase SRXL1 of this basidiomycete.