title: Natural-abundance isotope ratio mass spectrometry as a means of evaluating carbon redistribution during glucose-citrate cofermentation by Lactococcus lactis.
abstract: The cometabolism of citrate and glucose by growing Lactococcus lactis ssp. lactis bv. diacetylactis was studied using a natural-abundance stable isotope technique. By a judicious choice of substrates differing slightly in their 13C/12C ratios, the simultaneous metabolism of citrate and glucose to a range of compounds was analysed. These end-products include lactate, acetate, formate, diacetyl and acetoin. All these products have pyruvate as a common intermediate. With the objective of estimating the degree to which glucose and citrate metabolism through pyruvate may be differentially regulated, the delta13C values of the products accumulated over a wide range of concentrations of citrate and glucose were compared. It was found that, whereas the relative accumulation of different products responds to both the substrate concentration and the ratio between the substrates, the delta13C values of the products primarily reflect the availability of the two substrates over the entire range examined. It can be concluded that in actively growing L. lactis the maintenance of pyruvate homeostasis takes precedence over the redox status of the cells as a regulatory factor.
authors.affiliation: Groupe de Fractionnement Isotopique de Métabolismes, Laboratoire d'Analyse Isotopique et Electrochimique de Métabolismes, Université de Nantes, France.
authors.forename: Mohamed
authors.initials: M
authors.lastname: Mahmoud
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Gentil
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Robins
mesh_terms: D002244:Carbon / Q000032:analysis / Q000378:metabolism; D002247:Carbon Isotopes; D002951:Citrates / Q000378:metabolism*; D005285:Fermentation; D005947:Glucose / Q000378:metabolism*; D013294:Lactococcus lactis / Q000378:metabolism*; D013058:Mass Spectrometry / Q000379:methods; D019289:Pyruvic Acid / Q000378:metabolism
chemical_list: D002247:Carbon Isotopes; D002951:Citrates; D002244:Carbon; D019289:Pyruvic Acid; D005947:Glucose