The effect of carbon dioxide availability on succinic acid production with biofilms of Actinobacillus succinogenes

Carbon dioxide serves as a co-substrate in succinic acid (SA) production by Actinobacillus succinogenes making it an important consideration in fermentation optimisation. In the current study, the availability of CO2 to the cell, as the dissolved CO2 concentration in the fermentation broth (Cc02), is shown to define three distinct steady-state regimes. At Cm, values between 8.4mM (36.8% saturation) and saturation (22.8 mM), there is no evidence of CO2 limiting SA productivity and flux to SA is constant. As Cco(2) is decreased, an upper Cco, threshold (36.8% saturation; 8.4 mM) is reached where metabolic flux distributions remain constant but SA productivity and substrate uptake start to decline with decreasing Cco(2) levels. A further decrease in Cco(2) leads to a lower Cco(2) threshold (17.1% saturation, 3.9 mM) where SA productivity continues to decrease with a concomitant shift in carbon flux away from SA towards C-3 fermentative pathways including ethanol. Since SA production is not limited at relatively low Cco(2) values (36.8% saturation), adequate CO2 supply to the ferrnenter can be achieved without requiring major CO2 sparging schemes which is favourable from an industrial processing perspective. (C) 2016 Elsevier B.V. All rights reserved.