A deficiency of citrate synthase results in constitutive expression of the glyoxylate pathway in Arthrobacter pyridinolis.

Previous studies of Arthrobacter pyridinolis indicated that during the first half of the growth cycle on D-fructose, the organism utilizes a respiration-coupled transport system and exhibits glyoxylate pathway activity; during the second half of the growth cycle, a phosphoenolypyruvate:D-fructose phosphotransferase system is used for transport and no glyoxylate pathway activity is found [Pelliccione et al. (1979) Eur. J. Biochem. 95, 69--75]. A citrate-synthase-deficient mutant had the following properties: (a) high constitutive levels of glyoxylate pathway enzymes on various substrates, while such levels were only found in the wild type when it was grown on acetate; (b) acetyl-CoA levels much higher than in the wild type grown on several different substrates, whereas other metabolite levels were similar in the two strains; and (c) under conditions for induction of the phosphotransferase system, the wild type exhibited at least twice as much phosphotransferase activity as the mutant strain. A mutant lacking acetyl-CoA synthetase exhibited no induction of the glyoxylate pathway in the presence of acetate, although acetate uptake was normal. The results indicate a role for acetyl-CoA as inducer of the glyoxylate pathway. They further suggest a possible role, perhaps indirect, in repression of the phosphotransferase system.