Bioethanol production by Saccharomyces cerevisiae using maize cobs saccharified by cellulases of Podoscypha bolleana and Podoscypha petalodes

This study aimed to optimize cellulase production from locally selected lignocellulosic substrates (maize cobs, cypress, and eucalyptus) and bioethanol production from saccharified maize cobs using Saccharomyces cerevisiae under solid-state fermentation. Fungal samples were collected from Karura Forest in Kenya, based on morphological variations. Ten fungi were selected and tested for cellulase production, with two positive species identified as Podoscypha bolleana km05 and Podoscypha petalodes km06. PCR amplification of isolates' DNA using ITS4 R and ITS86 F primers along with phylogenetic analysis was conducted for accurate identification. The crude enzyme harvested was used to determine cellulase activity. Higher activities were recorded on untreated and pretreated maize cobs compared to other substrates. On untreated maize cobs, P. bolleana km05 yielded higher β-glucosidase on the 12th day (646.8 ± 21.0 IU/ml) and endoglucanase on the 9th day (2.63 ± 0.1 IU/ml). P. petalodes km06 yielded higher FPase (1.38 ± 0.03 IU/ml) and exoglucanase (0.78 ± 0.03 IU/ml) on the 3rd day of incubation. However, on pretreated maize cobs, P. bolleana km05 recorded higher FPase (1.51 ± 0.01 IU/ml) with 0.1 M HCl at 60°C for 1 h. Whereas, higher yields of endoglucanase (2.97 ± 0.2 IU/ml) and β-glucosidase (511.1 ± 10.1 IU/ml) were produced by P. bolleana km05. P. petalodes km06 recorded higher exoglucanase (0.74 ± 0.08 IU/ml) with 0.1 M HCl at 121°C. Cellulase of P. petalodes km06 yielded higher fermentable sugars with an 8 % substrate concentration (10.63 ± 0.70 mg/ml) at 72 h during saccharification. Cellulase of P. bolleana km05 produced higher bioethanol (37.30 ± 0.72 mg/ml) on maize cobs with a 20 % substrate loading at 96 h during fermentation. The supremacy of maize cobs as the most viable for producing cellulase and bioethanol is established. • Cellulase enzyme activities, saccharification and bioethanol production were investigated under SSF conditions. • Substrate treatments, incubation times and substrate loading concentrations were optimized. • A significant difference was observed when the substrate was subjected to acid pretreatment. • Maize cobs are found to be the most viable substrate for producing cellulases for saccharification and bioethanol production. • Fungal isolates from decaying biomass are a good source of cellulases