Culture-dependent isolation and optimization of cellulase-producing fungi from brewer’s spent grains

Abstract

The study involved isolating and optimizing cellulase-producing fungi from brewer's spent grain. Carboxylmethyl-cellulose (CMC) agar was used for the pour plate technique to screen the fungi. Based on the morphology of their colonies and other microscopic features, isolates were identified using lactophenol staining. The diameter and clear zones of colonies were evaluated to determine their hydrolysis efficiencies. The procedures used to optimize cellulase production were investigated using statistical Central Composite Design (CCD). Thirty-two microorganisms were isolated and screened for cellulolytic potential and only two (6.25%) demonstrated promising features. The prospective isolates were confirmed to be Aspergillus nidulans and Aspergillus oryzae. When prepared starch agar plates were flooded with iodine solution, A.nidulans and A.oryzae had hydrolysis efficiencies of 45.8% and 40%, respectively. A. nidulans had an optimal activity of 0.35UmL-1 at pH7 and 60°C and A. oryzae with optimal activity of 0.3UmL-1 at pH5 and 55°C. Moreover, A.nidulans had an optimal cellulase activity of 0.37UmL-1 at a temperature of 52.5°C and an incubation period of 30h, whereas A. oryzae gave up an optimal activity of 0.33UmL-1 at a temperature of 52°C and an incubation period of 26h, as a result of the influence of temperature and incubation period. The two isolates were good cellulase producers, however, the study revealed that A.nidulans produced cellulase more effectively than A. oryzae.