Utilization of Monosaccharide and Mixed Sugars by Clostridium Acetobutylicum
|Keywords||Clostridium acetobutylicum ATCC824 glucose xylose mixed sugar pH control|
Due to energy shortages and climate change in past decades, more intensive researches have been carried out on the conversion of abundant lignocellulosic biomass to sustainable biofuels and chemicals such as ethanol and butanol. Many countries, including Brazil, European countries, USA, and China have embraced the use of biofuels as an attempt to lessen dependence on petroleum and reduce air pollution and mitigate climate change.D-glucose, L-arabinose, D-mannose, D-xylose are saccharification products of lignocellulose and also important carbon sources for industrial fermentation. These sugars were evaluated for Acetone-butanol-ethanol (ABE) fermentation by Clostridium acetobutylicum ATCC824. The utilization efficacy of the five reducing sugars for the fermentation was in the order of D-glucose, L-arabinose, D-mannose, D-xylose.D-xylose is the second most abundant component in the lignocellulosic hydrolysate. Since carbon catabolite repression (CCR), microorganisms tend to consume the mixed sugars sequentially. We found that adding CaCO3or NaOH, could increase D-xylose consumption, when it was the only carbon source.Addition of1.0g/L butyric acid reduced the excessive accumulation of organic acids, increased the cell growth and enhanced solvent production. The concentration of ABE was12.84g/LIn order to test the utilization of mixed sugar by C. acetobutylicum ATCC824, media containing D-glucose and D-xylose at different ratios (1:2,1:5,1.5:1,2:1) were then evaluated for the ABE fermentation. When pH was controlled and glucose: xylose was1:5, a256.9%increase in xylose utilization and263.7%rise in solvent production were observed. When the ratio was1:2, xylose utilization rose from7.5%to81%, and solvent production increased by48%. These results may provide optimized conditions for further increasing the efficiency of lignocellulosic hydrolysate fermentation.