However, the duration of
butanol production increased with decreasing pH (Fig. 5A), resulting
in higher overall butanol concentrations (Fig. 4A) and yields
(Table 1). These results indicate that there is a clear advantage to
slowing down the fermentation rate to produce more butanol
and less PDO. The butanol production rate (Fig. 5A) closely mimics
the CO2 formation rate (Fig. 2A), while the PDO production rate
appears not to be correlated. This can be explained by the fact that
CO2 is an inevitable by-product on the pathway leading to butanol,
while no CO2 formation occurs when converting glycerol to PDO.