CO2 production, O-2 consumption and isocitrate dehydrogenase in the marine bacterium Vibrio natriegens

The respiratory metabolism of the marine bacterium Vibrio natriegens growing in batch cultures with acetate and pyruvate as carbon sources was studied. In particular, the relationship of the activity of the enzyme isocitrate dehydrogenase (IDH) to physiological CO2 production and O-2 consumption was examined. Gas measurements were performed by a new type of respirometer that combined O-2 detection by a Pb-O fuel cell and CO2 detection by infrared absorption. Two different respiratory patterns were observed. On pyruvate, CO2 production and O-2 consumption rates paralleled each other during the exponential and the stationary phases. On acetate, they did not. Growth based on acetate was characterized by a higher O-2 consumption, lower CO2 production, lower respiratory quotient and lower IDH activity than on pyruvate. In both culture media, the in vitro IDH activity remained elevated after the in vivo CO2 production had decreased when the carbon source was exhausted. The range of the respiratory quotient obtained in the acetate cultures suggests that the acetate is partitioned between the Krebs cycle and the glyoxylate bypass in the proportions of 1:4 to 1:2. In the pyruvate cultures, the range of the respiratory quotients indicates that, in the course of the different growth phases, the partitioning of the carbon source between the Krebs cycle and the anaplerotic pathways is variable.