Butanol fermentation.

This review provides an overview on bacterial butanol production and recent developments concerning strain improvement, newly built butanol production plants, and the importance of alternative substrates, especially lignocellulosic hydrolysates. The butanol fermentation using solventogenic clostridial strains, particularly Clostridium acetobutylicum, is a very old industrial process (acetone-butanol-ethanol-ABE fermentation). The genome of this organism has been sequenced and analysed, leading to important improvements in rational strain construction. As the traditional ABE fermentation process is economically unfavourable, novel butanol production strains are being developed. In this review, some newly engineered solvent-producing Clostridium strains are described and strains of which sequences are available are compared with C. acetobutylicum. Furthermore, the past and present of commercial butanol fermentation are presented, including active plants and companies. Finally, the use of biomass as substrate for butanol production is discussed. Some advances concerning processing of biomass in a biorefinery are highlighted, which would allow lowering the price of the butanol fermentation process at industrial scale.