Optimizing the production of rice straw hydrolytic cellulase under solid-state fermentation using Aspergillus terreus RS2

Abstract

Background The enzymatic hydrolysis of lignocelluloses into fermentable sugars is the key step in biorefining, and cellulases are the key enzymes. The low titer of cellulase production and their high cost remain the most significant barriers to their industrial applications. The aim of this study was the economic production of cellulase by an Egyptian fungal isolate under solid-state fermentation by using rice straw as a carbon source. Additionally, the produced enzyme can be applied in the hydrolysis of rice straw and production of free sugars that can be used in several biotechnological industries. Materials and methods The isolated fungus was identified according to its cultural and morphological features followed by 18S rDNA sequencing. Optimization of the enzyme productivity was performed by applying Plackett–Burman and Box–Behnken designs. Finally, the hydrolysis of rice straw for the production of fermentable sugars using the produced enzyme was carried out, confirmed by scanning electron microscope and thin-layer chromatography analysis. Results and conclusion The optimum cellulase activity produced by the isolated fungus Aspergillus terreus RS2 was 124.94 U/g dry substrate. It was achieved at the optimum conditions that were conducted to be as follows: 3.75 g (1.5%w/v) of rice straw moistened with 11.25 ml (1 : 3 biomass to moistening agent) of modified Mandel’s medium [1% (NH4)2SO4 was the only constituent nitrogen source] of pH 7, incubated at 30°C for 8 days. Finally, the activity of the produced enzyme in the degradation of rice straw indicated the release of reducing sugars of 343.98 mg/g dry substrate with a saccharification percentage of 34.4% recorded after 4-h hydrolysis period.