Elucidation of enzyme control mechanisms using macroscopic measurements in a mixed substrate fermentation system

Abstract

The objective of this work was to relate macroscopically measurable on-line fermentation parameters such as dissolved oxygen, off-gas oxygen and carbon dioxide, and cell mass, to the controlled production of key intracellular enzymes under carbon limited conditions. Both batch and perturbed batch aerobic fermentations were performed using two different strains of Escherichia coli, with glucose and lactose as the sole carbon sources. The two strains differed from each other only in the lac operon region of their genome. The parent strain, E. coli 3000, was inducible for the enzyme beta-galactosidase. The other strain, E. coli 3300, was a constitutive mutant in the production of beta-galactosidase. In all experiments, off-line assays of sugars and beta-galactosidase activity were performed. It was observed that there is a clear relationship between the macroscopic on-line measurements, dissolved oxygen tension, carbon dioxide evolution rate and oxygen uptake rate, and the microscopic control phenomena of catabolite repression, catabolite inhibition, and inducer repression.