Interrelationship of sugar metabolism (glucose, galactose, lactose) by Leuconostoc mesenteroides subsp mesenteroides

Abstract - Growth of Leuconostoc mesenteroides subsp mesenteroides strain 19D on either glucose, lactose and galactose alone or in combination was studied. Growth on galactose was slow and addition of lactose or glucose to cells growing on galactose increased the growth rate and decreased galactose utilization. β-Galactosidase was synthesized in the presence of glucose, but the enzyme level was 2-3-fold higher in lactose grown cells. Galactokinase was strongly repressed by glucose but induced by galactose and lactose. Galactose did not accumulate in the media, suggesting that lactose transport was not via a lactose-galactose antiport. The fermentation balance of glucose, lactose and galactose generally agreed with the theoretical values, but in the presence of galactose and lactose, small quantifies of formic acid and more acetate instead of ethanol were produced. Lactose was used rapidly alone, but slowly in the presence of galactose. In this case, a slight accumulation of glucose was observed, resulting in partial decrease of galactokinase activity and suggesting the repression of galactose metabolism.

Résumé - Interrelation entre les métabolismes des sucres (glucose, lactose, galactose) par Leuconostoc mesenteroides subsp mesenteroides
On a réalisé l'étude de la croissance et l'analyse enzymatique des cellules de Leuconostoc mesenteroides subsp mesenteroides (souche WD) en milieu MRS additionné d'un des sucres glucose, lactose, galactose ou de leurs combinaisons 2 à 2. Il apparaît que la β-galactosidase est synthétisée en présence du glucose mais plus faiblement qu'en présence du lactose. La galactokinase réprimée par le glucose est induite par le lactose et le galactose. Au cours de l'utilisation du lactose, le galactose n'est pas accumulé, ce qui exclut un système de transport de type antiport lactose-galactose. L'hétérofermentation du lactose et galactose est caractérisée par une production supérieure d'acétate en comparaison à l'hétérofermentation du glucose. Le galactose ralentit l'utilisation du lactose, ce qui conduit à une accumulation du glucose, donc à la répression de la galactokinase.