Biochemistry of filamentous fungi. IV. The significance of the tricarboxylic acid cycle in the oxidation of acetate by Penicillium chrysogenum

Metabolic flux distributions in Penicillium chrysogenum during fed-batch cultivations

Based on a review of the Penicillium chrysogenum biochemistry a stoichiometric model has been set up. The model considers 61 internal fluxes and there are 49 intracellular metabolites which are assumed to be in pseudo-steady state. In addition to the intracellular fluxes the model considers the uptake of 21 amino acids. From the stoichiometric model the maximum theoretical yield of penicillin V is calculated to 0.43 mol/mol glucose. If biosynthesis of cysteine is by direct sulfhydrylation rather than by transsulfuration, the maximum theoretical yield is about 20% higher, i.e., 0.50 mol/mol glucose. The theoretical yield decreases substantially if alpha-aminoadipate is converted to 6-oxo-piperidine-2-carboxylic acid (OPC). If only 40% of the alpha-aminoadipate is recycled, the maximum theoretical yield is 0.31 mol/mol glucose. The uptake rates of glucose, lactate, gamma-aminobutyrate, and 21 amino acids were measured during fed-batch cultivations. The rates of formation of penicillin V, delta-(L-alpha)-aminoadipyl-L-cysteinyl-D-valine (ACV), OPC, and the pool of isopenicillin N, 6-APA, and 8-HPA were also measured. Finally the synthesis rates of the biomass constituents RNA/DNA, protein, lipid, carbohydrate, and amino carbohydrate were measured. From these measured rates and the stoichiometric model the metabolic fluxes through the different intracellular pathways are calculated. The calculations show that penicillin formation is accompanied by a large flux through the pentose phosphate (PP) pathway due to a large requirement for nicotinamide-adenine dinucleotide phosphate (NADPH) used in the biosynthesis of cysteine. If cysteine is added to the medium, the flux through the PP pathway decreases. From the stoichiometric model Y(xATP) is calculated to 87 mmol adenosine triphosphate (ATP)/g dry weight (DW), and from the flux calculations m(ATP) is found to 3 mmol ATP/g DW/h. (c) 1995 John Wiley & Sons, Inc.

Dipicolinic acid synthesis in Penicillium citreo-viride

Hodson, Phillip H. (University of Texas, Austin), and J. W. Foster. Dipicolinic acid synthesis in Penicillium citreo-viride. J. Bacteriol. 91:562-569. 1966.-Dipicolinic acid (DPA) accumulation in culture filtrates of the mold Penicillium citreo-viride was studied in surface and submerged cultures. Good DPA yields were obtained in suspensions of washed, submerged mycelium in the presence of a carbon and a nitrogen source but in the absence of other minerals essential for growth. Fumaric acid was the only other acid formed in significant amounts. Glucose and glycerol were superior to various salts of organic acids as carbon sources, and certain amino acids were excellent nitrogen sources. l-Leucine, l-norvaline, l-tyrosine, and l-histidine were superior to urea, NH(4)Cl, or NaNO(3) as nitrogen precursors for DPA production. d-Norvaline was useless for DPA production. Glycerol-2-C(14) and -1-C(14), C(14)O(2), and l-leucine-C(14), l-tyrosine-C(14), and l-histidine-C(14) were tested as precursors in conjunction with suitable carbon and nitrogen sources. The DPA was decarboxylated chemically, and the distribution of C(14) was determined in the pyridine-C and in the carboxyl-C. The data are consistent with Martin and Foster's suggestion for bacteria that the DPA molecule is formed by a condensation of C(3) plus C(4) precursors, the resulting 2-keto, 6-aminopimelic acid derivate undergoing ring closure to form a heterocyclic precursor of DPA. The C(14)O(2) experiments indicate that oxaloacetate is formed by beta-carboxylation of pyruvate, this in turn probably becoming aspartic acid beta-semialdehyde, the C(4) compound which condenses with a second pyruvate. The enhancement of DPA formation by l-norvaline, l-leucine, and l-histidine is not ascribable to their functioning either as a source of nitrogen or carbon. l-Tyrosine, in a glycerol medium, contributed nearly 40% of the DPA carbon. The mechanism of biosynthesis of C(7) straight-chain and cyclic compounds is discussed.

UTILIZATION OF ACETATE, PYRUVATE, AND CO2 BY PENICILLIUM DIGITATUM

The utilization of C14 specifically labelled pyruvate, acetate, and CO2 by proliferating Penicillium digitatum cells has been studied by means of a series of time-course experiments. Pyruvate appeared to be utilized by way of acetate and the latter was in turn utilized mainly via the TCA processes. Degradation studies on aspartic acid and glutamic acid isolated from cells grown on acetate-1-C14 or C14O2 indicated that CO2 can be fixed in this organism by means of a two-stage process onto a "C2 unit"; the latter is thought to be derived from glyoxalic acid produced in the "glyoxalate bypass" pathway.