Optimization of levan biosynthesis from Bacillus siamensis using batch and continuous stirred-tank bioreactors: A response surface methodology approach

Abstract

Levan, a promising fructan polysaccharide for biopharmaceuticals, has limited large-scale production studies. This research optimized and scaled up levan biosynthesis from Bacillus siamensis in continuous stirred-tank bioreactors based on response surface methodology (RSM). Batch cultures optimized for 30 % (w/v) sucrose, pH 5.0, and 48 h incubation yielded a maximum 15.74 % (w/v) levan. The optimal batch conditions were evaluated in a continuous stirred-tank bioreactor, where dilution rates and mixing speeds were examined. At a dilution rate of 0.021 h⁻¹ and an agitation speed of 200 rpm, the maximum productivity was 17.96 % (w/v), and steady-state conditions were attained after three days of continuous fermentation. X-ray diffraction confirmed the amorphous nature of the levan, ideal for biomaterial applications. These results underline the potential of B. siamensis for high-yield levan production and provide a systematic approach for bioprocess parameter optimization, serving as a strong basis for its increased application in industrialized polysaccharide-based bioprocessing.