(191ag) Investigating Clostridium Carboxidivorans P7 Metabolisms during Syngas Fermentations

Clostridium Carboxidivorans P7 is a model microorganism for industrial syngas fermentation. This study used ¹³C tracers to delineate functional pathways and to profile metabolic responses to syngas substrates as well as mass transfer. Labeling of P7 proteinogenic amino acids suggests: deficient biosynthesis capability for some key amino acids (such as phenylalanine and leucine); active Re-citrate synthase to complete the TCA pathway (but no citramalate synthase detected); bicarbonate utilization via pyruvate:ferredoxin oxidoreductase and anaplerotic pathways. To investigate the effect of syngas mass transfer on cell metabolism, inverse dynamic labeling was performed in continuous-flow-stirred-tank reactors (i.e., P7 culture was prepared in a ¹³C-medium then fed with unlabeled syngas feedstock). In tested conditions, P7 metabolized CO/CO₂ after 5-hour acclimation and the key metabolite Acetyl-CoA was labeled at the speed of 0.010~0.016 hour^-1 (flow rates ranging from 10mL/min to 20mL/min). Mass transfer was proved to be more influential on energy metabolism (cofactor generation) than carbon flux. However, syngas substrates showed strikingly slower rates percolating through central pathways, which demonstrate different sensitivity to substrates mass transfer conditions. Decrease of syngas flow rates from 20mL/min to 1 mL/min would not significantly hamper gaseous carbon utilization rates, but high flowrate facilitates NAD(P)H generation and increases ratio of ethanol in fermentation products.