Improvement of Fungal Cellulase Production by Mutation and Optimization of Solid State Fermentation

Spores of Aspergillus sp. SU14 were treated repeatedly and sequentially with Co60 gamma-rays, ultraviolet irradiation, and N-methyl-N'-nitro-N-nitrosoguanidine. One selected mutant strain, Aspergillus sp. SU14-M15, produced cellulase in a yield 2.2-fold exceeding that of the wild type. Optimal conditions for the production of cellulase by the mutant fungal strain using solid-state fermentation were examined. The medium consisted of wheat-bran supplemented with 1% (w/w) urea or NH4Cl, 1% (w/w) rice starch, 2.5 mM MgCl2, and 0.05% (v/w) Tween 80. Optimal moisture content and initial pH was 50% (v/w) and 3.5, respectively, and optimal aeration area was 3/100 (inoculated wheat bran/container). The medium was inoculated with 25% 48 hr seeding culture and fermented at 35degrees C for 3 days. The resulting cellulase yield was 8.5-fold more than that of the wild type strain grown on the basal wheat bran medium.

Fungal Strain Improvement for Cellulase Production Using Repeated and Sequential Mutagenesis

A fungal strain producing a high level of cellulase was selected from 320 fungal isolates and identified as Aspergillus sp. This strain was further improved for cellulase production by sequential treatments by two repeated rounds of gamma-irradiation of Co60, ultraviolet treatment and four repeated rounds of treatment with N-methyl-N'-nitro-N-nitrosoguanidine. The best mutant strain, Aspergillus sp. XTG-4, was selected after screening and the activities of carboxymethyl cellulase, filter paper cellulase and beta-glucosidase of the cellulase were improved by 2.03-, 3.20-, and 1.80-fold, respectively, when compared to the wild type strain. After being subcultured 19 times, the enzyme production of the mutant Aspergillus sp. XTG-4s was stable.

Production of Aerial Conidia of Lecanicillium lecanii 41185 by Solid-State Fermentation for Use as a Mycoinsecticide

The production of aerial conidia of Lecanicillium lecanii 41185, a highly virulent fungus, by solid-state fermentation was studied for use as a biocontrol agent against aphids. Among several agro-industrial solid media, steamed polished rice was found to produce the highest amount of aerial conidia. The optimal conditions for aerial conidia production were determined to be a 28.5% moisture content in the rice, 25degrees C culture temperature, rice pH of 6.0, 75% ambient relative humidity, 4-dold seeding culture, 0.6% KNO3, and 12 d of culture time. The conidia yield increased from 5.7 x 10(9) conidia/g polished rice to 18.2 x 10(9) conidia/g polished rice following application of these optimized conditions.