Bioprocess Optimization for Levan Production by Bacillus subtilis B58

Abstract

Levan is an extracellular polysaccharide composed of fructose (fructans) with wide applications in pharmaceutical and chemical industries. The objectives of this research are to develop production medium through statistical optimization of medium composition in shake flask level, and bioprocess optimization for levan production by Bacillus subtilis B58 in 16-L bioreactor. At first, growth kinetic profiles for un-optimized medium yielded a maximal cell mass of 1.94 g L-1 and maximal levan production of 13.5 g L-1. Secondly, this medium was further optimized through Fractional Factorial Design of the main components that can influence levan production; i.e. sucrose, yeast extract, K2HPO4 and MgSO4.7H2O. Further optimization was achieved by Box-Behnken design, through which the optimum new medium formulation supporting higher levan production contained (g L-1): sucrose, 130; yeast extract, 6.3 and K2HPO4, 5.0. Levan production increased up to 61.4% after the statistical optimization of medium components. Further optimization was achieved by transferring the cultivation process to 16-L bioreactor under controlled and uncontrolled pH conditions. The results showed that the uncontrolled cultivation condition was more favorable for levan production, where the maximal cell mass production in the bioreactor reached 5.05 g L-1 and the maximal levan production reached 26.65 g L-1. In conclusion, this study successfully produced levan up to 97.4% higher than that obtained in shake flask level after optimizing the production medium and the bioreactor cultivation conditions.