Ammonium acetate increases the production of butanol by Clostridium beijerinckii cultures growing in sweet sorghum juice
1Ibaraki univ. agri.
A sustainable biofuel production needs cheaper feedstock and improved fermentation performance. Regarding the feedstock, sweet sorghum, Sorghum bicolor (L) Moench has been identified as a superior biofuel feedstock because of its fermentable sugar-rich biomass yield under a wide range of environmental conditions. Because biobutanol is a promising next generation biofuel, we have studied the fermentative production of butanol using sweet sorghum juice (SSJ). Here we report that ammonium acetate (AA) enhances butanol production in Clostridium beijerinckii cultures growing in SSJ. Five strains of C. beijerinckii (JCM 1390T, JCM 7828, JCM 7844, JCM 7845, and SBP2-HB) were used in this study. Strain SBP2-HB is our isolate from a upland soil sample through an enrichment culture with SSJ. Strains were grown anaerobically at 37°C in charcoal-treated, 1.3-fold diluted SSJ. Sugars and fermentation products were determined by HPLC. In the SBP2-HB cultures, the addition of 15 mM AA resulted in a 3-fold increase in butanol production and no further increase was found in the presence of 30 and 60 mM AA. Neither NH4Cl nor ammonium acetate led to this enhancement effect. The enhancement of butanol production was partly explained by an increased sugar consumption. The other four strains were examined for whether AA had the same enhancement effect or not. When the amount of AA added was fixed at 30 mM, the highest (3.3-fold increase) and the lowest (1.6-fold increase) enhancement was found with JCM 1390T and JCM 7845, respectively. The ability to produce butanol in SSJ was different in these five strains. Among them, the highest producer is SBP2-HB which produced about 110 mM butanol in SSJ supplemented with 30 mM AA. Further studies are now in progress to analyze the fermentation pathway shift caused by AA.
keywords:biobutanol,sweet sorghum,Clostridium beijerincki