Improvements of Metabolites Tolerance in Clostridium acetobutylicum by Micronutrient Zinc Supplementation

Micronutrient zinc is of great importance for acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum. The effect of zinc supplementation on toxic metabolites (formic, acetic, butyric acid and butanol) tolerance during ABE fermentation was investigated under various stress-shock conditions without pH control. Great improvements on cell growth, glucose utilization and butanol production were achieved. In the presence of 0.45 g/L formic acid, zinc contributed to 11.28 g/L butanol produced from 55.24 g/L glucose compared to only 5.27 g/L butanol from 29.49 g/L glucose in the control without zinc supplementation. More importantly, relatively higher levels of 7.5 g/L acetic acid, 5.5 g/L butyric acid and 18 g/L butanol could be tolerated by C. acetobutylicum with zinc supplementation while no fermentation was observed under the same stress-shock condition respectively, suggesting that the acids and butanol tolerance in C. acetobutylicum could be significantly facilitated by pleiotropic regulation of micronutrient zinc. Thus, this paper provides an efficient bioprocess engineering strategy for improving stress tolerance in Clostridium species.