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Factors Affecting the Pathways of Glucose Catabolism and the Tricarboxylic Acid Cycle in Pseudomonas natriegens

Department of Bacteriology, University of Georgia, Athens, Georgia

ABSTRACT

Less than 50% of theoretical oxygen uptake was observed when glucose was dissimilated by resting cells of Pseudomonas natriegens. Low oxygen uptakes were also observed when a variety of other substrates were dissimilated. When uniformly labeled glucose-¹⁴C was used as substrate, 56% of the label was shown to accumulate in these resting cells. This material consisted, in part, of a polysaccharide which, although it did not give typical glycogen reactions, yielded glucose after its hydrolysis. Resting cells previously cultivated on media containing glucose completely catabolized glucose and formed a large amount of pyruvate within 30 min. Resting cells cultivated in the absence of glucose catabolized glucose more slowly and produced little pyruvate. Pyruvate disappeared after further incubation. In this latter case, experimental results suggested (i) that pyruvate was converted to other acidic products (e.g., acetate and lactate) and (ii) that pyruvate was further catabolized via the tricarboxylic acid cycle. Growth on glucose repressed the level of key enzymes of the tricarboxylic acid cycle and of lactic dehydrogenase. Growth on glycerol stimulated the level of these enzymes. A low level of isocitratase, but not malate synthetase, was noted in extracts of glucose-grown cells. Isocitric dehydrogenase was shown to require nicotinamide adenine dinucleotide phosphate (NADP) as cofactor. Previous experiments have shown that reduced NADP (NADPH₂) cannot be readily oxidized and that pyridine nucleotide transhydrogenase could not be detected in extracts. It was concluded that acetate, lactate, and pyruvate accumulate under growing conditions when P. natriegens is cultivated on glucose (i) because of a rapid initial catabolism of glucose via an aerobic glycolytic pathway and (ii) because of a sluggishly functioning tricarboxylic acid cycle due to the accumulation of NADPH₂ and to repressed levels of key enzymes.