CO2 PRODUCTION, O-2 CONSUMPTION AND ISOCITRATE DEHYDROGENASE IN THE MARINE BACTERIUM VIBRIO NATRIEGENS

The respiratory metabolism of the marine bacterium Vibrio natriegens g rowing in batch cultures with acetate and pyruvate as carbon sources w as studied. In particular, the relationship of the activity of the enz yme isocitrate dehydrogenase (IDH) to physiological CO2 production and O-2 consumption was examined. Gas measurements were performed by a ne w type of respirometer that combined O-2 detection by a Pb-O fuel cell and CO2 detection by infrared absorption. Two different respiratory p atterns 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 charact erized by a higher O-2 consumption, lower CO2 production, lower respir atory quotient and lower IDH activity than on pyruvate. In both cultur e media, the in vitro IDH activity remained elevated after the in vivo CO2 production had decreased when the carbon source was exhausted. Th e range of the respiratory quotient obtained in the acetate cultures s uggests that the acetate is partitioned between the Krebs cycle and th e glyoxylate bypass in the proportions of 1:4 to 1:2. In the pyruvate cultures, the range of the respiratory quotients indicates that, in th e course of the different growth phases, the partitioning of the carbo n source between the Krebs cycle and the anaplerotic pathways is varia ble.