Yeast extract promotes phase shift of bio-butanol fermentation by Clostridium acetobutylicum ATCC824 using cassava as substrate

When fermenting on cassava (15–25%, w/v) with Clostridium acetobutylicum ATCC824, a severe delay (18–40 h) was observed in the phase shift from acidogenesis to solventogenesis, compared to the cases of fermenting on corn. By adding yeast extract (2.5 g/L-broth) into cassava meal medium when the delay appeared, the phase shift was triggered and fermentation performances were consequently improved. Total butanol concentrations/butanol productivities, compared to those with cassava substrate alone, increased 15%/80% in traditional fermentation while 86%/79% in extractive fermentation using oleyl alcohol as the extractant, and reached the equivalent levels of those using corn substrate. Analysis of genetic transcriptional levels and measurements of free amino acids in the broth demonstrated that timely and adequate addition of yeast extract could promote phase shift by increasing transcriptional level of ctfAB to 16-fold, and indirectly enhance butanol synthesis through accelerating the accumulation of histidine and aspartic acid families.

► A severe delay of phase shift was found in fermentation using cassava substrate.
► Yeast extract added during delay period promoted initiation of solventogenesis.
► Performances of traditional and extractive runs were improved by yeast extract.
► Real-time PCR was investigated to analyze transcriptional levels of genes.
► This process can produce butanol from cassava, a cheap non-grain crop.