Co-fermentation of glucose and citrate by Lactococcus lactis diacetylactis: quantification of the relative metabolic rates by isotopic analysis at natural abundance.
The simultaneous catabolism of citrate and glucose by growing Lactococcus lactis subsp. lactis biovar. diacetylactis to obtain energy was followed quantitatively, using a non-enrichment isotopic technique. Both citrate and glucose are precursors of pyruvate, which may either be reduced to lactate, the principle product that accumulates, or be converted to diacetyl and acetoin. Under suitable conditions, both routes regenerate NAD+. Until recently, however, the quantitative relationships between the two substrates and these three products were poorly defined. It was recently shown, by exploiting differences in natural abundance 13C/12C ratios in the two substrates, that there is no metabolic separation of the catabolism of these two carbon sources. In this study, it is shown that the relative consumption rates change throughout the growth phase, citrate being preferentially metabolised at the onset of a culture of energy-depleted cells, with a subsequent evolution towards a metabolism dominated by glucose consumption. Additionally, it is shown that the relative consumption rates are influenced by environmental factors, notably initial pH and temperature.
Isotopic Fractionation in Metabolism Group, LAIEM, CNRS UMR6006, Faculté des Sciences et des Techniques, 2 rue de la Houssinière, 44322 Nantes, France.
S
S
Goupry
E
E
Gentil
S
S
Akoka
R J
RJ
Robins
D000085:Acetates / Q000378:metabolism; D000093:Acetoin / Q000378:metabolism; D019343:Citric Acid / Q000378:metabolism*; D003931:Diacetyl / Q000378:metabolism; D005285:Fermentation; D005947:Glucose / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D019344:Lactic Acid / Q000378:metabolism; D013294:Lactococcus lactis / Q000254:growth & development / Q000378:metabolism*; D019289:Pyruvic Acid / Q000378:metabolism; D013696:Temperature
D000085:Acetates; D019343:Citric Acid; D019344:Lactic Acid; D019289:Pyruvic Acid; D000093:Acetoin; D005947:Glucose; D003931:Diacetyl