Purification and characterization of extracellular dextranase from a novel producer, Hypocrea lixii F1002, and its use in oligodextran production

Abstract

Fungi were isolated from natural soil samples and screened for extracellular dextranase synthesis. The strain F1002 was identified as Hypocrea lixii using a standard internal transcribed spacer ribosomal DNA analysis and was selected for extracellular dextranase synthesis. The enzyme was purified via ammonium sulfate precipitation and Sepharose 6B chromatography, which resulted in an 8.3-fold increase in the specific activity and a 10.73% recovery. This enzyme is a monomeric protein with a molecular mass of 62kDa, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme, which was identified as an endodextranase, had an optimum pH of 5.0 and an optimum temperature of 25°C. The dextranase activity was enhanced by Mg2+, Al3+, and especially Zn2+ at a low concentration, which improved its activity to 124.22%. The enzyme has a very high hydrolytic affinity toward high-molecular weight dextrans. Setting the concentrations of the H. lixii F1002 dextranase (2.31U/mL) and dextrans (6%), as well as the reaction time (45min), allowed the dextranase to hydrolyze dextrans of controlled molecular weights (20–70kDa). Three types of oligodextrans with different molecular weights (namely, 69,376, 38,251, and 21,364Da) were obtained, with a total yield of 80.32%.