Ex situ product recovery and strain engineering of Clostridium acetobutylicum for enhanced production of butanol

To reduce butanol toxicity, adsorptive fermentation has been extensively studied. In this study, SP850 was systematically selected as an optimal adsorbent showing high butanol selectivity. In the flask culture involving in situ butanol recovery fermentation using Clostridium acetobutylicum ATCC 824 and the adsorbent, production of acetone, butanol, and ethanol (ABE) increased by 46.8%. An acid crash, however, occurred in the ex situ recovery fermentation using SP850. This problem was solved by homologous expression of the adhE1 gene in the ATCC 824 strain. During the ex situ recovery fermentation by the adhE-overexpressing strain, 34.2 g/L of ABE was produced from 132.8 g/L of glucose. In the 146-h continuous mode of ex situ fermentation, the strain produced 205.6 g/L of ABE (146.9 g/L of butanol) from 605.3 g/L of glucose. Our results indicate that proper selection of an adsorbent and strain engineering for the ex situ recovery fermentation is effective at enhancing butanol fermentation.