Abstract:

In order to improve the production of lactic acid and succinic acid by C. crenatum, the effect of sodium
bicarbonate on the yield of succinic acid and lactic acid was investigated. Sodium bicarbonate had a significant effect on
glucose consumption rate and organic acid production rate of C. crenatum under oxygen deprivation. With the addition
of 100 mmol/L of sodium bicarbonate, the glucose consumption rate increased by 130%, reaching 69.14 mmol/(L•h),
and the lactic acid accumulation showed an increase from 184.10 mmol/L to 400.92 mmol/L. When the concentration
of added sodium bicarbonate reached 200 mmol/L, the concentration of accumulated succinic acid was 128.05 mmol/L,
which indicated a 9.2-fold increase compared to no addition of sodium bicarbonate, and the total yield of lactic acid and
succinic acid was 1.9 mol/mol. Further analysis showed that sodium bicarbonate activated phosphoenolpyruvate carboxylase
(PEPC) in C. crenatum. PEPC activity increased from 0.956 U/mg to 1.242 U/mg in the presence of 100 mmol/L of sodium
bicarbonate. The flux from phosphoenolpyruvate (PEP) to oxaloacetate increased 3 times and the flux from PEP to pyruvate
decreased 18.9%. Metabolic flux analysis indicated that 96% of succinic acid was produced through the C4 pathway. The
results of this study indicate lactic acid and succinic acid can be produced by C. crenatum under oxygen deprivation even
though their proliferation is arrested.

Key words: Corynebacterium crenatum, metabolic flux analysis, succinic acid, lactic acid, sodium bicarbonate