Metabolic flux analysis on succinic acid production from crude glycerol by Actinobacillus succinogenes

Abstract

Conversion of the surplus crude glycerol from biodiesel industry to succinic acid (SA), a commodity biochemical for bioplastic production is an interesting approach to increase economic value of this by-product. In this study, the optimization of crude glycerol and MgCO3 concentrations for succinic acid production by Actinobacillus succinogenes in batch fermentation was studied in a laboratory-scale bioreactor.The maximum succinic acid concentration and production yield were 14.44 ± 0.11 g/L and 1.58 ± 0.12 gSA/ginitial Gly using 1% (w/v) crude glycerol as the carbon source supplemented with 10 g/L of MgCO3 to increase dissolved CO2 in the system. Metabolic flux analysis (MFA) on the SA production was analyzed using MetaFluxNet program to evaluate the impact of initial crude glycerol concentrations and MgCO3 supplementation. Phosphoenolpyruvate (PEP) to oxaloacetate node was identified as an objective function. The high crude glycerol concentration was found to result in low succinic acid production due to the presence of minor chemical components such as sodium chloride in the crude glycerol which affected PEP carboxykinase and pyruvate kinase, targeting on the energy balance of the cells. The addition of MgCO3 was suggested to promote succinic acid production. The crude glycerol was converted to succinic acid mainly through C4 pathway compared to C3 pathway under all conditions. Besides, acetic acid is an indicator that shows the divergence from succinic acid production under all conditions. The work demonstrates insights on developing an efficient SA production process from crude glycerol by this potent microbe.