Enzymatic Regulation of Glucose Catabolism by Lactobacillus plantarum in an Aerobic Chemostat

The influence of oxygen on the metabolic regulation of glucose catabolism by Lactobacillus plantarum 8014 was examined in a chemostat (D=0.2 h⁻¹, pH 5.5). A steadystate anaerobic culture was shifted to an aerobic condition by imposing an oxygen transfer rate of 1.84 mmol L⁻¹ min⁻¹. Enzyme activities, end product concentrations, and ATP levels were determined during the resultant transition and under steady‐state aerobic conditions. During the transition, oxygen was consumed by the aerobic culture and the intracellular ATP concentration increased until hydrogen peroxide, which also increased, became inhibitory. Under the aerobic condition, the steady‐state specific rate of substrate utilization and acetate production increased. The lactate dehydrogenase, NAD‐dependent lactate dehydrogenase, acetate kinase, pyruvate oxidase, and NADH oxidase specific activities all increased under aerobic conditions. Changes in the intracellular lactate and acetate concentrations had a temporal correspondence with the changes in the aforementioned catabolic activities. Subsequent experiments using chloramphenicol to inhibit de novo protein synthesis and kinetic analysis of crude enzyme extracts suggested that these changes were due to both changes in synthesis and activity levels.