In the absence of significant product,
substrate or other inhibition, decreasing fermentation pH resulted
in slower fermentations, higher butanol and lower PDO yields. The
rate of PDO production fluctuated in a multimodal manner, unlike
the production rate of CO2 and butanol, suggesting that PDO production
is regulated and further that its regulation may serve to
function in redox homeostasis and allow C. pasteurianum to behave
non-biphasic. In batch culture, process pH can be used as a tool to
control the product profile at the expense of fermentation time.