Characterization of Cellulase from Geotrichum candidum Strain Gad1 Approaching Bioethanol Production

Out of 61 fungal isolates, Geotrichum candidum GAD1 isolated from a marine algal sample belonging to the coastline of Abo Qir, Alexandria, Egypt, that was molecularly identified with accession no. MN638741 is the most potent strain producing cellulase degrading carboxymethylcellulose salt (CMC). Dox medium was optimized using OFAT design with CMC as the sole carbon source giving high productivity of cellulase enzyme with incubation period 6 days at 180 rpm, at pH 7, and 30 °C. Ammonium sulfate of fraction 50% gave the highest specific activity 209.1 U/mg and gave a single protein band (72 KDa) using SDS–PAGE. Maximum purified cellulase activity (49.78 U/mL) was reported at pH 7, 45 °C, and 10% salinity and was stable between (40–60 °C) and (pH 4.0–10.0). In addition, different inhibitors and activators were tested, and subsequently, it was reported that all tested heavy metal ions (Fe 2+ , Co 2+ , Mg 2+ , Ca 2+ , Na + , Mn 2+ , and K + ) were significantly affected, especially, Fe 2+ (10 mM) giving a double-fold increase in cellulase activity, while EDTA, petroleum ether, and n -Hexane exerted a suppression action. The kinetic V max and K m for CMC degradation were 238.09 µM/min and 0.42 mg/mL, respectively. Optimized purified cellulase approaching bioethanol production from pretreated rice straw and CMC as substrates was achieved with maximum bioethanol yield of 11.9 g g −1 and 13.2 g g −1 , respectively, and conversion efficiency by GC–MS; 90.4% and 87.4%, respectively. Conclusively, the presented cellulase profile could be applied as an efficient alternative biofuel source as renewable energy under different industrial scales.