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Journal of Bacteriology, February 2000, p. 1136-1143, Vol. 182, No. 4
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

The Metabolic Network of Lactococcus lactis: Distribution of 14C-Labeled Substrates between Catabolic and Anabolic Pathways

L. Novák and P. Loubiere*

Centre de Bioingénierie Gilbert Durand, UMR CNRS 5504, UR 792 INRA, Institut National des Sciences Appliquées, Complexe Scientifique de Rangueil, F-31077 Toulouse Cedex 4, France

Received 22 April 1999/Accepted 22 November 1999

Lactococcus lactis NCDO 2118 was grown in a simple synthetic medium containing only six essential amino acids and glucose as carbon substrates to determine qualitatively and quantitatively the carbon fluxes into the metabolic network. The specific rates of substrate consumption, product formation, and biomass synthesis, calculated during the exponential growth phase, represented the carbon fluxes within the catabolic and anabolic pathways. The macromolecular composition of the biomass was measured to distribute the global anabolic flux into the specific anabolic pathways. Finally, the distribution of radiolabeled substrates, both into the excreted fermentation end products and into the different macromolecular fractions of biomass, was monitored. The classical end products of lactic acid metabolism (lactate, formate, and acetate) were labeled with glucose, which did not label other excreted products, and to a lesser extent with serine, which was deaminated to pyruvate and represented approximately 10% of the pyruvate flux. Other minor products, keto and hydroxy acids, were produced from glutamate and branched-chain amino acids via deamination and subsequent decarboxylation and/or reduction. Glucose labeled all biomass fractions and accounted for 66% of the cellular carbon, although this represented only 5% of the consumed glucose.

* Corresponding author. Mailing address: INSA, Département de Génie Biochimique et Alimentaire, 135 Ave. de Rangueil, F-31077 Toulouse Cedex 4, France. Phone: (33) 5 61 55 94 38. Fax: (33) 5 61 55 94 02. E-mail: loubiere{at}insa-tlse.fr.

Journal of Bacteriology, February 2000, p. 1136-1143, Vol. 182, No. 4
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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