Mathematical model of growth and polyhydroxybutyrate production using microbial fermentation of Bacillus subtilis

Abstract

ABSTRACTPoly-3-hydroxybutyrate (PHB) has been extensively utilized as a biodegradable plastic. The value of substrate inhibition constant (KI) was also established in shake flask cultures by varying the initial glucose concentration (20–160 g/L) in growth media. Excess carbon source adversely affected the growth of Bacillus subtilis cultures. The production kinetics of PHB was studied using batch fermentation strategy for B. subtilis culture. Batch cultivation was also performed in a 5-L stirred tank bioreactor to obtain a Biomass and PHB yield of 5.25 and 1.6 g/L, respectively. The kinetic data of biomass, PHB production, and substrate consumption was used to estimate the optimized values of the growth and product formation kinetic parameters. Optimal values of kinetic parameters (µm value of 0.325, KS value of 10.53 g/L for glucose, Y value of 0.183 g/g of glucose, KI value of 105 g/L, m value of 0.12 g/(g h), k1 of 0.36 g/g, and k2 value was 0.12 g/(g h)) and the initial values of biomass, substrate and PHB concentration (X = 0.14 g/L, S = 9.99 g/L, and P = 0.13 g/L) were utilized to obtain a modified mathematical model for PHB production. Statistical validity of the mathematical model simulations were measured using F-test. The F-test showed that the statistical validity of the model was more than 95% when compared with experimentally obtained values. This model also predicted that the production of PHB using B. subtilis cultures is mainly growth associated.