A general inhibition kinetics model for ethanol production using a novel carbon source: sodium gluconate

In this study, sodium gluconate was applied as a novel carbon source for the fuel ethanol production using an engineered Escherichia coli strain KO11 in batch fermentations. Ethanol and acetic acid were produced as two major products as well as small amount of lactic acid during the fermentation. Compared to the conventional carbon source glucose, the bioconversion of sodium gluconate possessed two distinct advantages: faster utilization rate of sodium gluconate (1.66 g/L per h) compared to glucose (0.996 g/L per h) and no requirement for pH control during fermentation. A general inhibition model including both substrate and products inhibitory effects was proposed, which adequately simulated batch fermentation kinetics at various concentrations of sodium gluconate. All of the products showed inhibitory effects on cell growth. The order of the inhibitory strength of all products and substrate was for the first time clarified in this study. Acetic acid was the most inhibitory product mitigating the cell growth, followed by ethanol and lactic acid. Sodium gluconate stimulated cell growth when its concentration was below 16 g/L, while it inhibited the cell growth when the concentration was above this concentration. It completely inhibited the cell growth when the concentration was 325 g/L. The high value of both the coefficient of determination (R (2)) and the adjusted R (2) verified the good fit of the model. This paper provides key insights into further engineering these strains to improve ethanol production.