Statistical optimization of kojic acid production by a UV-induced mutant strain of Aspergillus terreus

ABSTRACT The ability of four Aspergillus strains for biosynthesis of kojic acid was evaluated among which Aspergillus terreus represented the highest level (2.21 g/L) of kojic acid production. Improvement kojic acid production ability of A. terreus by random mutagenesis using different exposure time to ultraviolet light (5-40 min) was then performed to obtain a suitable mutant of kojic acid production (designated as C5-10, 7.63 g/L). Thereafter, design of experiment protocol was employed to find medium components (glucose, yeast extract, KH2PO4 (NH4)2SO4, and pH) influences on kojic acid production by the C5-10 mutant. A 25-1 fractional factorial design augmented to central composite design showed that glucose, yeast extract, and KH2PO4 were the most considerable factors within the tested levels (p < 0.05). The optimum medium composition for the kojic acid production by the C5-10 mutant was found to be glucose, 98.4 g/L; yeast extract, 1.0 g/L; and KH2PO4, 10.3 mM which was theoretically able to produce 120.2 g/L of kojic acid based on the obtained response surface model for medium optimization. Using these medium compositions an experimental maximum Kojic acid production (109.0 ± 10 g/L) was acquired which verified the efficiency of the applied method.

Enhanced alkaline cellulases production by the thermohalophilic Aspergillus terreus AUMC 10138 mutated by physical and chemical mutagens using corn stover as substrate

Abstract A thermohalophilic fungus, Aspergillus terreus AUMC 10138, isolated from the Wadi El-Natrun soda lakes in northern Egypt was exposed successively to gamma and UV-radiation (physical mutagens) and ethyl methan-sulfonate (EMS; chemical mutagen) to enhance alkaline cellulase production under solid state fermentation (SSF) conditions. The effects of different carbon sources, initial moisture, incubation temperature, initial pH, incubation period, inoculum levels and different concentrations of NaCl on production of alkaline filter paper activity (FPase), carboxymethyl cellulase (CMCase) and β-glucosidase by the wild-type and mutant strains of A. terreus were evaluated under SSF. The optimum conditions for maximum production of FPase, CMCase and β-glucosidase were found to be the corn stover: moisture ratio of 1:3(w/v), temperature 45 °C, pH range, 9.0–11.0, and fermentation for 4, 4 and 7 day, respectively. Inoculum levels of 30% for β-glucosidase and 40% for FPase, CMCase gave the higher cellulase production by the wild-type and mutant strains, respectively. Higher production of all three enzymes was obtained at a 5% NaCl. Under the optimized conditions, the mutant strain A. terreus M-17 produced FPase (729 U/g), CMCase (1,783 U/g), and β-glucosidase (342 U/g), which is, 1.85, 1.97 and 2.31-fold higher than the wild-type strain. Our results confirmed that mutant strain M-17 could be a promising alkaline cellulase enzyme producer employing lignocellulosics especially corn stover.

Comparación de los efectos provocados por el calor y la irradiación sobre Aspergillus parasiticus / Comparison of effects resulting from the application of physical treatments to Aspergillus parasiticus

El propósito de este trabajo fue estudiar la inhibición de la produción de aflatoxinas asociadas al crecimiento del hongo Aspergillus parasiticus NRRL 2999, mediante el empleo de radiaciones ionizantes. El hongo fue cultivado en arroz de tipo comercial en condiciones de temperatura y humedad ideales para la producción de toxinas. Los cultivos así obtenidos fueron irradiados con dosis de 1,5 kGy* (2D10) al cabo de distintos tiempos de desarrollo, observándose que la máxima inhibición de la producción de toxinas se alcanzaba al irradiar cultivos de 20 horas de desarrollo. Asimismo, se estudió el efecto del calor y su combinación con la irradiación sobre la producción de aflatoxinas, la cual fue seguida a lo largo de 11 días de desarrollo de los cultivos. El contenido de toxinas de los distintos cultivos se dosó por dilución a estinción en cromatografía de capa delgada. Los resultados obtenidos mostraron que, tanto un calentamiento de 15 min a 55-C, como la irradiación de los cultivos con una dosis de 1,5kGy, disminuyen el contenido de toxinas, siendo este último processo el más efectivo. Más aún, la combinación de estos dos agentes físicos, irradiando los cultivos inmediatamente después de ser sometidos al calentamiento, reduce los niveles de toxinas por debajo de los límites de detección sugeridos por las organizaciones mundiales de la salud