Clostridium carboxidivorans Fermentation of Syngas Produces Butanol and Hexanol: Medium Development and Culture Technique

Butanol and hexanol from fermentation can be blended with petroleum fuels for transportation and used in the existing fuel infrastructure.  These higher alcohols are superior fermentation products compared to the dominant biofuel, ethanol.  Clostridium carboxidivorans grown in defined medium under high CO partial pressure produced about 1 g/L of each butanol and hexanol when Cu was omitted from the medium and the concentration of Mo in the medium was increased 10X.  Mo and other trace metals are essential for growth of C. carboxidivorans.  When Cu was omitted or when Mo was increased, more carbon from syngas was fixed into products.  Clostridium strain P20, closely related to C. carboxidivorans, responded differently to Cu omission.  Mo may compete with W in enzyme active sites.  N and P were reduced in the defined medium, and MES, NaCl and Cu were omitted to reduce medium cost.  Reduction of N to 4 mM and P to 0.4 mM supported growth of C. carboxidivorans.  The present study shows that butanol and hexanol can be produced by syngas fermentation in a low cost medium.  It was also found that additional empirical factors, such as inoculum size, are important for culture maintenance and fermentation control.