Energy-independent uptake of iron from citrate by isolated outer membranes of Neisseria meningitidis.

Cyanide-poisoned Neisseria meningitidis SD1C cells rapidly took up 55Fe from iron-citrate complexes during the first 2 min, after which no further iron was accumulated. [14C]citrate was not taken up concomitantly with 55Fe by these cells. The 55Fe taken up by the poisoned cells was found in the membrane fraction after cells were broken; 70% of the radioactivity was distributed in the outer membrane, and 30% was in the inner membrane. Isolated outer membranes from iron-starved cells were as capable of iron uptake from citrate as intact cells were. As with whole cells, [14C]citrate was not taken up by isolated outer membranes. A polyacrylamide gel electrophoresis analysis of the proteins from citrate-dialyzed outer membranes after the uptake of 55Fe revealed that the radioactivity was associated with a major band of 36,500 molecular weight.

Citrate cycle and related metabolism of Listeria monocytogenes.

The growth response of Listeria monocytogenes strains A4413 and 9037-7 to carbohydrates was determined in a defined medium. Neither pyruvate, acetate, citrate, isocitrate, alpha-ketoglutarate, succinate, fumarate, nor malate supported growth. Furthermore, inclusion of any of these carbohydrates in the growth medium with glucose did not increase the growth of Listeria over that observed on glucose alone. Resting cell suspensions of strain A4413 oxidized pyruvate but not acetate, citrate, isocitrate, alpha-ketoglutarate, succinate, fumarate, or malate. Cell-free extracts of strain A4413 contained active citrate synthase, aconitate hydratase, isocitrate dehydrogenase, malate dehydrogenase, fumarate hydratase, fumarate reductase, pyruvate dehydrogenase system, and oxidases for reduced nicotinamide adenine dinucleotide and reduced nicotinamide adenine dinucleotide phosphate. The alpha-ketoglutarate oxidation system, succinate dehydrogenase, isocitrate lyase, and malate synthase were not detected. Cytochromes were not detected. The data suggest that strain A4413, under these conditions, utilizes a split noncyclic citrate pathway which has an oxidative portion (citrate synthase, aconitate hydratase, and isocitrate dehydrogenase) and a reductive portion (malate dehydrogenase, fumarate hydratase, and fumarate reductase). This pathway is probably important in biosynthesis but not for a net gain in energy.