The role of some membrane dehydrogenases in Pseudomonas fluorescens.

The membrane-associated oxidative enzymes glucose, gluconate, and malate dehydrogenases were examined in psychrotrophic Pseudomonas fluorescens. The function and activity of these enzymes was determined by measuring extracellular product formation by washed cell suspensions. Membrane dehydrogenase activities and corresponding transport activities for the substrates glucose, gluconate and malate were compared in batch cultures grown with these substrates at 30 and 5 degrees C. These activities correlated with the production or lack of extracellular oxidation products. in chemostat cultures grown at 30 and 5 degrees C, the membrane enzymes and production of their extracellular oxidation products appeared to be regulated by the available carbon concentration. The enzymes were induced and high concentrations of extracellular oxidation products were produced under conditions of nitrogen limitation (carbon excess) but not carbon limitation. The lower affinities of the three membrane enzymes for their respective substrates, when compared with the transport systems utilizing the same substrates, correlated with the observed major function of these enzymes in carbon-excess environments. The primary role of the membrane-associated oxidative enzymes, in carbon dissimilation by this psychrotrophic microorganism at low temperatures in carbon-excess environments, was strongly implicated.