Engineering microorganisms to produce a variety of biofuels and commodity chemicals from sugars is a promising technology, but those products are often toxic to the cells at industrial levels and subsequently lower the titer and productivity. Efflux pumps are a natural mechanism for alleviating toxicity by secreting fuels and inhibitory chemicals from the cell. Recently, C. tyrobutyricum, a super-butyrate producer with butyrate and acetate as two major fermentation products, has been engineered to produce butanol as the main product by overexpressing the bifunctional aldehyde/alcohol dehydrogenase gene adhE2. However, the toxicity of butanol to the cells remains a challenge to the fermentation process. In this study, we overexpressed endogenous efflux pump gene AcrB in butanol-producing C. tyrobutyricum mutants and investigated its effect on alleviating butanol toxicity in those mutants. Mutants overexpressing AcrB showed improved butanol tolerance and higher butanol production in batch fermentation.
