Metabolic flux analysis elucidates the importance of the acid-formation pathways in regulating solvent production by Clostridium acetobutylicum

Metabolic flux analysis was used to investigate the roles of the acid formation pathways in Clostridium acetobutylicum. The acid formation pathways were revealed to serve different roles in wildtype fermentations than previously expected. Specifically, enzymes known to catalyze butyrate formation were found to uptake butyrate without concomitant production of acetone. This role was further corroborated by flux analysis of a recombinant strain overexpressing the butyrate formation enzymes. Analysis of wildtype fermentation data also revealed an important role for the acetate formation enzymes, namely the cycling of carbon between acetate and acetylCoA during the stationary phase. Next, metabolic flux analysis was used to compare the patterns of activity in two butyrate kinase deficient strains of C. acetobutylicum. The strain developed by gene inactivation, PJC4BK, exhibited a shift in acid formation fluxes toward acetate while the strain developed by antisense RNA strategies, 824(pRD4), did not exhibit such a shift. However, both strains exhibited altered solvent formation patterns. PJC4BK exhibited a strong transient enhancement of solvent formation fluxes. In contrast, 824(pRD4) exhibited relatively lower levels of solvent formation fluxes, although fluxes were sustained over a longer period of time.