Comparative chemical and biological optimized saccharification pretreatment of rice straw by local fungal strains with native cbh1 gene expression

Abstract

Burning rice straw has generated harmful risks to human health and the environment. The world’s energy requirements are constantly rising due to growth and sustainable development in different countries. Rice straw represents the potential source for replacing fossil fuels as a sustainable and renewable feedstock for energy generation; it was calculated to be about 3.5 million tons annually in Egypt. This study aims to compare fungal and chemical pretreatment to improve the saccharification of rice straw for biofuel production. Rice straw and three fungal strains (two isolates, Trichoderma saturnisporum MN1-EGY (T. saturnisporum), Aspergillus niger MN2-EGY (A. niger), and standard strain Pleurotus ostreatus NRRL 3501 (P. ostreatus)) were used to achieve this purpose. A cellulolytic enzyme complex, including exoglucanase (FP-ase), endoglucanase (CMC-ase), β-glucosidase, and xylanase, was determined during all incubation periods of fungal-treated rice straw. Pretreatment of rice straw with 1.5% NaOH achieved the most efficient delignification, reducing lignin content from 18.40 to 4.40% and resulting in a weight loss of 45%. Under these conditions, a cellulase enzyme cocktail from T. saturnisporum and A. niger achieved a saccharification yield of 0.4 g glucose/g dry substrate. A. niger exhibits the highest gene expression fold of cbh1 with 0.5-folds, while T. saturnisporum showed 0.4-fold gene expression; P. ostreatus showed 0.2 folds of gene expression.