Effect of redox potential regulation on succinic acid production by Actinobacillus succinogenes

Abstract

The effects of redox potential used as a control parameter on the process of succinic acid production in batch cultures of Actinobacillus succinogenes NJ113 have been investigated. In batch fermentation, cell growth and metabolite distribution were changed with redox potential levels in the range of −100 to −450 mV. From the results, the ORP level of −350 mV was preferable, which resulted in high succinic acid yield (1.28 mol mol⁻¹), high succinic acid productivity (1.18 g L⁻¹ h⁻¹) and high mole ratio of succinic acid to acetic acid (2.02). The mechanism of redox potential regulation was discussed by metabolic flux analysis and the ratio of NADH/NAD⁺. We expected that redox potential can be used as a valuable parameter to monitor and control much more anaerobic fermentation production.

Appendix

Metabolic reactions:

$$ \begin{gathered} \left( {{\text{r}}_{ 1} } \right){\text{ Glucose}} + {\text{ATP}} = {\text{G6P}} + {\text{ADP}} \hfill \\ \left( {{\text{r}}_{ 2} } \right){\text{ G6P}} = {\text{F6P}} \hfill \\ \left( {{\text{r}}_{ 3} } \right){\text{ F6P}} + {\text{ATP}} = {\text{FBP}} + {\text{ADP}} \hfill \\ \left( {{\text{r}}_{ 4} } \right){\text{ FBP}} = 2 {\text{GAP}} \hfill \\ \left( {{\text{r}}_{ 5} } \right){\text{ GAP}} + {\text{ADP}} + {\text{NAD}}^{ + } = {\text{PEP}} + {\text{ATP}} + {\text{NADH}} + {\text{H}}_{ 2} {\text{O}} \hfill \\ \left( {{\text{r}}_{ 6} } \right){\text{ PEP}} + {\text{ADP}} = {\text{PYR}} + {\text{ATP}} \hfill \\ \left( {{\text{r}}_{ 7} } \right){\text{ PYR}} + {\text{CoA}} + {\text{NAD}}^{ + } = {\text{ACA}} + {\text{CO}}_{{ 2 }} + {\text{NADH}} \hfill \\ \left( {{\text{r}}_{ 8} } \right){\text{ ACA}} + {\text{Pi}} = {\text{CoA}} + {\text{Ac}} - {\text{P}} \hfill \\ \left( {{\text{r}}_{ 9} } \right){\text{ Ac}} - {\text{P}} + {\text{ADP}} = {\text{Acetate}} + {\text{ATP}} \hfill \\ \left( {{\text{r}}_{ 10} } \right){\text{ PYR}} + {\text{NADH}} = {\text{Lactate}} + {\text{NAD}}^{ + } \hfill \\ \left( {{\text{r}}_{ 1 1} } \right){\text{ PYR}} + {\text{CoA}} = {\text{Formate}} + {\text{ACA}} \hfill \\ \left( {{\text{r}}_{ 1 2} } \right){\text{ ACA}} + 2 {\text{NADH}} = {\text{Ethanol}} + {\text{CoA}} + 2 {\text{NAD}}^{ + } \hfill \\ \left( {{\text{r}}_{ 1 3} } \right){\text{ PEP}} + {\text{CO}}_{ 2} + {\text{ADP}} = {\text{OAA}} + {\text{ATP}} \hfill \\ \left( {{\text{r}}_{ 1 4} } \right){\text{ OAA}} + {\text{NADH}} = {\text{MAL}} + {\text{NAD}}^{ + } \hfill \\ \left( {{\text{r}}_{ 1 5} } \right){\text{ MAL}} = {\text{FUM}} + {\text{H}}_{ 2} {\text{O}} \hfill \\ \left( {{\text{r}}_{ 1 6} } \right){\text{ FUM}} + {\text{NADH}} = {\text{Succinate}} + {\text{NAD}}^{ + } \hfill \\ \left( {{\text{r}}_{ 1 7} } \right){\text{ G6P}} + {\text{H}}_{ 2} {\text{O}} + 2 {\text{NADP}} = {\text{RL5P}} + {\text{CO}}_{ 2} + 2 {\text{NADPH}} \hfill \\ \left( {{\text{r}}_{ 1 8} } \right){\text{ RL5P}} = {\text{X5P}} \hfill \\ \left( {{\text{r}}_{ 1 9} } \right){\text{ RL5P}} = {\text{R5P}} \hfill \\ \left( {{\text{r}}_{ 20} } \right){\text{ R5P}} + {\text{X5P}} = {\text{S7P}} + {\text{GAP}} \hfill \\ \left( {{\text{r}}_{ 2 1} } \right){\text{ S7P}} + {\text{GAP}} = {\text{E4P}} + {\text{F6P}} \hfill \\ \left( {{\text{r}}_{ 2 2} } \right){\text{ X5P}} + {\text{E4P}} = {\text{F6P}} + {\text{GAP}} \hfill \\ \left( {{\text{r}}_{ 2 3} } \right){\text{ ATP}} = {\text{ADP}} + {\text{Pi}} \hfill \\ \end{gathered} $$

(r_BM) 0.0102 G6P + 0.0032 F6P +0.0364 GAP + 0.0131 PEP + 0.0685 PYR + 0.0746 ACA + 0.0372 OAA + 0.0154 R5P + 0.0077 E4P + 1.1640 ATP + 0.3334 NADPH = Biomass + 1.1640 ADP + 0.3334 NADP.