Isopropanol-butanol-ethanol (IBE) production in repeated-batch cultivation of Clostridium beijerinckii DSM 6423 immobilized on sugarcane bagasse

Abstract

The IBE mixture is a potential automotive fuel, and its production by Clostridium beijerinckii DSM 6423, the best known natural IBE producer, is hindered by low productivity and low butanol titer. To alleviate this problem, we cultivated C. beijerinckii DSM 6423 in repeated batches using sugarcane bagasse as a low-cost immobilization agent. Experiments were conducted in 250-mL bottles containing 150 mL P2 medium, glucose, and bagasse. In a fermentation with seven batch cycles (257 h) containing 7.5 g bagasse, glucose (60 g/L) conversion varied between 38% and 98%. In four of the batch cycles, IBE productivity was between 0.22 and 0.28 g/L∙h, and butanol titer reached 6.7–8.6 g/L. In contrast, in a free-cell single-batch cultivation, glucose conversion was limited to 35%, IBE production was slower (0.13 g IBE/L∙h), and butanol titer did not exceed 4.8 g/L. Despite the gains in productivity and butanol titer, further research is needed to elucidate the factors and mechanisms that caused IBE yield to decline during repeated-batch cultivation of C. beijerinckii DSM 6423.