studied the enzyme levels in
C. acetobutylicum DSM 1732 at phosphate limited chemostats performed
at pH 4.3 and 6. At pH 4.3 predominantly solvents were
produced and high activity of the coenzyme A-transferase with
acetate or butyrate was measured as compared to pH 6, where
mostly acids were formed. Overall activities of in vitro enzymes
correlated well with the formation of the corresponding acids or
solvents. Hüsemann and Papoutsakis (1989a,b) extensively elucidated
the mechanism of solvent formation by looking at in vitro
and in vivo enzyme activities and the limitation of these enzymes
in continuous cultures of C. acetobutylicum ATCC 824 under various
bioreactor conditions. They found that gassing acidogenic culture
with carbon monoxide pulsing with butyrate or glucose resulted
in an increase in activities of acetaldehyde dehydrogenase (AYHD)
and butyraldehyde dehydrogenase (BYHD), with a parallel increase
in specific rates of ethanol and butanol formation. In pure acidogenic
glucose-grown cultures (pH 6) BYDH activity and butanol
formation were unobserved. Vasconcelos et al. (1994) and Girbal
et al. (1995) made a similar observation that for glucose-grown
cultures at pH 6.5 only acids and small amounts of ethanol are
formed but when the substrate is a mixture of glucose and glycerol
then high ethanol and butanol dehydrogenase activities are
detected resulting in alcohol production.