Purification and Characterization of an Extracellular Lipase Produced by Aspergillus oryzae ST11 as a Potential Catalyst for an Organic Synthesis

Abstract

The lipase producing Aspergillus sp. ST11 was identified by molecular and morphological methods. The primers ITS1/ITS4 were used for amplifying the ITS region. It showed that the strain was grouped with Aspergillus oryzae and Aspergillus flavus (98 % bootstrap value). The colony morphology of Aspergillus sp. ST11 on malt extract agar and Czapek yeast agar showed a characteristic of A. oryzae. Therefore, it was identified as Aspergillus oryzae ST11. The lipase produced by the strain was purified and characterized. The purification steps involved precipitation with chilled acetone and separation by column chromatography, with HiTrap® Q HP and Toyopearl Butyl-650M, respectively. After purification, the lipase activity was increased 13 fold and with 7.9 % yield. Its molecular mass was 25 kDa. The purified lipase was stable at a pH between 5.0 - 8.0 and had optimum activity at pH 7.5. It was stable at 30 °C and had optimum activity at 37 °C. Its activity was promoted in the presence of Mg2+ but it was greatly decreased in the presence of Co2+, Cu2+, Hg2+ and Zn2+. Surfactants (Triton X-100, Tween-80, Tween-20, arabic gum, and sodium dodecyl sulfate) showed negative effects on lipase activity, while inhibitors (PMSF, EDTA, and β-mercaptoethanol) did not reduce the activity significantly. Polar solvents, such as methanol and ethanol, had much negative effect on lipase activity compared to non-polar solvents, such as hexane and isooctane. The concentrated lipase from A. oryzae ST11 was used to catalyze the transesterification and gave the highest bioconversion (90 %) after 24 h. HIGHLIGHTS Extracellular lipase produced by Aspergillus oryzae ST11 could be applied in many applications which is more flexible compared with the use of whole-cell biocatalysts High stability toward a wide range of pH and temperature obtained from this extracellular lipase The concentrated lipase shows the capability to produce the high biodiesel from natural oil GRAPHICAL ABSTRACT