Physiology and metabolism of pathogenic neisseria: tricarboxylic acid cycle activity in Neisseria gonorrhoeae

Abstract

Tricarboxylic acid [TCA] cycle activity was examined in N. gonorrhoeae CS-7. The catabolism of glucose in N. gonorrhoeae by a combination of the Entner-Doudoroff and pentose phosphate pathways resulted in the accumulation of acetate, which was not further catabolized until the glucose was depleted or growth became limiting. Radiorespirometric studies revealed that the label in the 1 position of acetate was converted to CO2 at twice the rate of the label in the 2 position, indicating the presence of a TCA cycle. Growth on glucose markedly reduced the levels of all TCA cycle enzymes except citrate synthase (EC 4.1.3.7). Extracts of glucose-grown cells contained detectable levels of all TCA cycle enzymes except aconitase (EC 4.2.1.3), isocitrate dehydrogenase (EC 1.1.1.42), and a pyridine nucleotide-dependent malate dehydrogenase (EC 1.1.1.37). Extracts of cells capable of oxidizing acetate lacked only the pyridine nucleotide-dependent malate dehydrogenase. Instead of this enzyme, a particulate pyridine nucleotide-independent malate oxidase (EC 1.1.3.3) was present. This enzyme required FAD for activity and may be associated with the electron transport chain. Radiorespirometric studies utilizing labeled glutamate demonstrated that a portion of the TCA cycle functioned during glucose catabolism. In spite of the presence of all TCA cycle enzymes, N. gonorrhoeae CS-7 was unable to grow in medium supplemented with cycle intermediates.