Screening and isolation of Bacillus isolates for Levansucrase activity and for Levan Production

Abstract

Levan, a fructan homoexopolysaccharide synthesized from sucrose, has gained significant industrial interest due to its antilipidemic, anticancer, and prebiotic properties. This study aimed to isolate and characterize high-yielding levan-producing Bacillus strains from diverse natural sources, including fermented foods, decayed fruits, sugarcane juice, and sugarcane field soils. Using sucrose-enriched media, ten Bacillus isolates were obtained, of which seven exhibited high viscosity and mucoid colony morphology on Cortezi medium, indicative of exopolysaccharide production. Among them, a single strain, Bacillus velezensis SR1, demonstrated the highest levansucrase activity (2.5 U/ml) and levan yield (1.2 g/ml) under submerged fermentation at 37°C and pH 6.5. Enzyme activity peaked at 48 hours before declining due to nutrient depletion. Structural characterization of the extracted levan using Fourier-transform infrared spectroscopy (FTIR) confirmed the presence of β-(2,6) glycosidic linkages with β-(1,2) branching, essential for its functional properties, revealing the spectral peaks observed at 3297 cm⁻¹, 1125 cm⁻¹, 1012 cm⁻¹, and 925 cm⁻¹, corresponding to O−H groups in fructose, C−O−H stretching, C−O−C stretching vibrations, and pyranose ring structures, respectively. Molecular identification via 16S rDNA sequencing revealed 99% similarity to Bacillus velezensis SR1, confirming its taxonomic identity. These findings highlight Bacillus velezensis SR1 as a promising strain for industrial levan production, offering potential applications in food, pharmaceutical, and biotechnological sectors.