A capnophilic rumen bacterium Mannheimia succiniciproducens produces succinic acid as a major fermentation end product under CO2-rich anaerobic condition. Since succinic acid is produced by carboxylation of C3 compounds during the fermentation, intracellular CO2 availability is important for efficient succinic acid formation. Here, we investigated the metabolic responses of M. succiniciproducens to the different dissolved CO2 concentrations (0-260 mM). Cell growth was severely suppressed when the dissolved CO2 concentration was below 8.74 mM. On the other hand, cell growth and succinic acid production increased proportionally as the dissolved CO2 concentration increased from 8.74 to 141 mM. The yields of biomass and succinic acid on glucose obtained at the dissolved CO2 concentration of 141 mM were 1.49 and 1.52 times higher, respectively, than those obtained at the dissolved CO2 concentration of 8.74 mM. It was also found that the additional CO2 source provided in the form of NaHCO3, MgCO3, or CaCO3 had positive effects 1 on cell growth and succinic acid production. However, growth inhibition was observed when excessive bicarbonate salts were added. By the comparison of the activities of key enzymes, it was found that PEP carboxylation by PEP carboxykinase (PckA) is the most important for succinic acid production as well as the growth of M. succiniciproducens by providing additional ATP.