Warner S. Wegener

Propionate oxidation in Escherichia coli

An investigation was undertaken to determine the principal pathway of propionate oxidation in Escherichia coli E-26. Studies in a number of systems have established that propionate may be metabolized by several different pathways. Since these pathways may be differentiated by the pattern of14CO2 evolution from specifically labelled carbon atoms of propionate, a radiorespirometric experiment was performed in which propionate-adapted E. coli E-26 was used. Under these conditions, both the rate and final cumulative percentage of14CO2 was greatest for 1-14C-propionate, intermediate for 2-14C-propionate, and least for 3-14C-propionate. The observed labelling pattern is consistent with oxidation of propionate to acetate via lactate.

Propionate metabolism: III. Studies on the significance of the α-hydroxyglutarate pathway☆

The characteristics of Escherichia coli E-26 and a derived mutant E-26V during adaptation to propionate have been examined. When transferred from a glucose citrate medium to a mineral salts medium containing propiouate as the sole source of carbon, E-26V initiated growth more quickly and formed a higher activity of α-hydroxyglutarate synthase than did the parent strain. Moreover, in E-26V, the formation of α-hydroxyglutarate synthase immediately preceded growth on propionate, whereas in E-26, enzyme activity was not detected until the mid to late exponential growth phase. In contrast, isocitrate lyase formation immediately preceded growth initiation in both the parent and mutant cultures. It is proposed that the α-hydroxyglutarate pathway is metabolically significant during growth of E. coli E-26V on propionate by providing an auxiliary mechanism for the formation of C4 acids. Such intermediates are essential for the formation of adaptive enzymes involved in the oxidation of propionate to acetate.

Propionate metabolism: V. The physiological significance of isocitrate lyase during growth of E. coli on propionate☆

Abstract The role of isocitrate lyase during growth on propionate was investigated using three strains (E-26, K-12, and W) of Escherichia coli . The activity of this enzyme during growth on propionate varied with respect to the strain employed, the concentration of propionate added to the mineral salts culture medium, and the phase of growth at which cells were harvested. The growth behavior of E-26 and of K-12 mutants indicates that in these strains of E. coli , the formation of C 4 acids from propionate can be accomplished either by the phosphoenolpyruvate (PEP) carboxylase pathway or by the glyoxylate bypass. In the early phase of growth, pyruvate formed from the oxidation of propionate is metabolized primarily via the PEP carboxylase pathway. In such cultures, the activity of isocitrate lyase and malate synthase is low. As growth proceeds, there occurs a shift in metabolism, such that the carboxylase pathway is inhibited and the decarboxylation of pyruvate to form acetyl-CoA is stimulated. In such cultures, the formation of the enzymes of glyoxylate bypass is derepressed. In contrast to E-26 and K-12, the formation of isocitrate lyase is not derepressed in E. coli W cultured on propionate.

Selection 0f mutants constitutive for several glyoxylatecondensing enzymes during growth on valeric acid

Abstract An investigation was undertaken to assess the formation of several glyoxylate condensing enzymes during growth on a series of short-chain fatty acids. When Escherichia coli was grown on acetate, high malate synthase and low β- n -propylmalate synthase activities were observed. Cells grown on either propionate or butyrate possessed high malate synthase activity, and in addition formed low levels of α-hydroxyglutarate, β-ethylmalate and β- n -propylmalate synthase activity. In contrast, growth on valerate effected high activity of all these glyoxylate condensing enzymes. Evidence is presented that valerate does not act to induce or derepress enzyme formation, but rather acts to select a mutant population which is constitutive for the formation of these enzymes. Such mutants also are able to grow with a much shorter lag on propionate, butyrate, valerate, caproate and heptanoate. The possible relationship between formation of these enzymes and growth on short-chain fatty acids is discussed.

An isotopic method for assaying the condensation of glyoxylate with acetyl-CoA and other short-chain fatty acid acyl-CoA derivatives

1. 1. An isotopic method has been described for assaying the malate synthetase reaction. This procedure is based on measuring the disappearance of 1-C14-glyoxylate as a function of acetyl-CoA. 2. 2. This assay is applicable for the determination of α-hydroxyglutarate, β-ethylmalate, and β-n-propylmalate synthetase activity. 3. 3. The method deseribed is specific and sensitive to changes in glyoxylate concentration of less than 0.001 μmole. 4. 4. This assay provides a sensitive and rapid procedure which can be used for investigating the enzymic condensations of glyoxylate with other short-ehain fatty acid acyl-CoA derivatives.

Propionate metabolism: IV. Significance of carboxylation reactions during adaptation to propionate☆

Abstract The data presented are concerned with factors regulating adaptation of Escherichia coli to growth on propionate. A mutant strain of E. coli E-26 was employed; this mutant grows on acetate and on a number of other substrates, but is unable to initiate growth when propionate is the sole source of carbon. The mutant possesses a functional tricarboxylic acid cycle and glyoxylate bypass; is able to oxidize propionate to acetate; but is unable to effect sufficient formation of C 4 acids required for initiation of growth on propionate. This deficiency can be overcome by the addition of either succinate or HCO 3 − to propionate media. It is proposed that the mutant is deficient in one or more carboxylation reactions, since such cells possess a markedly decreased capacity to incorporate 14 CO 2 into cell material. It is further suggested that carboxylation reactions are most active during initiation of growth on propionate and decline as growth proceeds.

Propionate metabolism: II. Factors regulating adaptation of Escherichia coli to propionate

Abstract Factors regulating adaptation of Escherichia coli to propionate have been examined. Evidence is presented that growth on propionate, in contrast to butyrate and valerate, involves adaptation rather than mutation-selection. The long lag preceding adaptation to this substrate is significantly reduced by the addition of limiting concentrations of C 4 acids to the medium. This C 4 acid effect is partially met by addition of HCO − 3 or vitamin B 12 to the medium, and suggests that this organism may possess a deficiency in the functioning of the propionyl-CoA carboxylase pathway. Evidence is presented that growth per se in the presence of propionate results in induction of enzymes which enable the cell to utilize propionate as the sole source of carbon. The metabolic pathway induced under such conditions appears to involve oxidation of propionate to acetate and CO 2 .