Natural paucity of anaplerotic enzymes: basis for dependence of Arthrobacter pyridinolis on L-malate for growth

Abstract

Previous work has shown that in Arthrobacter pyridinolis the transport systems for glucose and several amino acids are respiration coupled, with malate oxidation occurring concomitantly with transport. The requisite malate has to be supplied exogenously, so that growth on glucose or certain amino acids only occurs if malate is also present in the medium. These and other data suggested that A. pyridinolis might be deficient in anaplerotic enzymes, which maintain intracellular levels of dicarboxylic acids. A comparative study was undertaken of anaplerotic enzymes in A. pyridinolis and in a closely related species, A. crystallopoietes, which has respiration-coupled transport of glucose but can grow on glucose without added malate. The paucity of anaplerotic enzymes in A. pyridinolis and its probable relationship to the malate requirement for growth on glucose were documented as follows: (i) A. crystallopoietes, but not A. pyridinolis, possesses phosphoenolpyruvate carboxylase activity, and neither species contains pyruvate carboxylase; (ii) both A. pyridinolis and A. crystallopoietes possess glyoxylate pathways that are induced by acetate but not by hexoses; (iii) isocitrate lyase-deficient mutants of A. pyridinolis fail to grow on rhamnose and fructose as well as acetate; and (iv) mutants of A. crystallopoietes that require malate for growth on glucose are deficient in phosphoenolpyruvate carboxylase.