Cellulase-producing Bacillus strains isolated from agricultural soils: Application in corn-residue hydrolysis and bioethanol production

This study aimed to isolate and characterize local Bacillus strains from agricultural soil samples collected in Aleppo, Syria, and to evaluate their ability to produce cellulase, which is the key enzyme responsible for the biodegradation of cellulose. Unlike studies limited to bacterial screening on model substrates, this work integrates strain selection, crude-enzyme production, corn-residue hydrolysis, and subsequent ethanol fermentation. A total of 19 bacterial strains were obtained, and three of them (BN1, BN4, and BN6, for Bacillus Number 1, 4, and 6) were selected based on their highest cellulolytic index values using carboxymethyl cellulose medium and Congo red staining. The results revealed significant differences among the strains, with BN4 exhibiting the highest enzymatic activity (7.45 U/ml) after 72 h of incubation, followed by BN6 with moderate activity, while BN1 showed the lowest activity. SDS-PAGE revealed a prominent protein band of approximately 42 kDa in the concentrated extracellular enzyme extract. When the enzymatic extract was applied to chemically pretreated corn residues (NaOH and H₂O₂), the amount of reducing sugars increased significantly, enabling higher production of bioethanol using baker’s yeast. Among the pretreatments, H₂O₂ yielded the highest bioethanol production (8.35% w). These findings indicate that local Bacillus strains, particularly BN4, have potential for converting agricultural residues into value-added products such as bioethanol. These findings may be particularly relevant to resource constrained post-war settings such as Syria, where locally available microbial resources and agricultural residues could support lower-cost biomass valorization and renewable biofuel production.