Optimization of Extracellular Cellulase Production from a Locally Isolated Bacillus subtilis Strain Using Response Surface Methodology

Abstract

ABSTRACT

Agricultural residues such as rice straw represent an abundant, low-cost substrate for microbial cellulase production, yet locally isolated strains from Al-Qadisiyah Governorate remain poorly characterized. In this template study, a cellulolytic bacterium (designated Bacillus subtilis QU-27) was isolated from decomposing rice straw and its extracellular cellulase activity optimized using a Box–Behnken response surface design across three factors: pH (5.5–7.5), incubation temperature (30–50 °C), and substrate concentration (0.5–2.5% w/v carboxymethyl cellulose). Enzyme activity was quantified using the dinitrosalicylic acid (DNS) method and expressed in U/mL. The model predicted maximum cellulase activity of 18.4 ± 0.6 U/mL at pH 6.5, 45 °C, and 1.5% substrate concentration, a result confirmed experimentally within 5% of the predicted value. Analysis of variance indicated the model was statistically significant (p < 0.05) with temperature exerting the largest individual effect on yield. These illustrative findings suggest that regionally isolated Bacillus strains can be optimized into efficient cellulase producers suitable for downstream applications in biofuel production and agricultural waste valorization. As a template document, all data presented are fictitious and intended only to demonstrate the expected structure, tone, and level of detail of a QJBT original research article.