Purification, biochemical characterization and antifungal activity of a novel Aspergillus tubingensis glucose oxidase steady on broad range of pH and temperatures

Abstract

This study was carried out to evaluate the in vitro and in vivo antifungal efficiency of Aspergillus tubingensis CTM 507 glucose oxidase (GOD) against plant pathogenic fungi. GOD displayed a wide inhibitory spectrum toward different fungi at a concentration of 20 AU. The GOD had a strong inhibitor effect on mycelia growth and spore germination of Pythium ultimum. Interestingly, the GOD exhibited a potent in vivo antifungal effect against P. ultimum responsible for potato plants disease. The antifungal GOD was purified 13-fold with 27 % yield and a specific activity of 3435 U/mg. The relative molecular mass of the GOD was 180 kDa by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The GOD activity was optimum at pH 4.5 and 60 °C. It was found to be stable over a large pH range (3–9). It also displayed a marked thermostability with a 50-min half-life at 65 °C. The 10 residues of the N-terminal sequence of the purified GOD (S–K–G–S–A–V–T–T–P–D) showed no homology to the other reported GOD, identifying a novel GOD. FTIR spectroscopic analysis revealed the presence of C–O and C=O groups corresponding to a d-glucono-lactone. The findings indicated that GOD is the first A. tubingensis-produced fungicide ever reported to exhibit such promising biological properties. It could become a natural alternative to synthetic fungicides to control certain important plant microbial diseases.