The co-metabolism of citrate plus xylose by Leuconostoc mesenteroides subsp. mesenteroides results in a growth stimulation, an increase in D-lactate and acetate production and repression of ethanol production. This correlated well with the levels of key enzymes involved. A partial repression of alcohol dehydrogenase and a marked stimulation of acetate kinase were observed. High citrate bioconversion yields in diacetyl plus acetoin were obtained at pH 5.2 in batch (11.5%) or in chemostat (up to 17.4%) culture. In contrast, no diacetyl or acetoin was detected in citrate plus glucose fermentation.

The conversion from citrate positive (Cit') to citrate negative (Cit-) phenotype of six strains of Leuconostoc mesenteroides was followed during growth in milk and buffered or unbuffered MRS medium at 30 or 37°C. High rate of loss of Cit' phenotype was observed. The Citphenotype was found to be linked to the loss of 22 to 23 kb plasmids. All Cit-mutants isolated from Leuc. mesenteroides subsp. cremoris 195 reverted spontaneously to the Cit' phenotype. Hybridization experiments using a 0.8 kb fragment of the citP gene of Leuc. mesenteroides showed that all the plasmids which were lost in Cit-mutants encoded for a citrate permease. However, neither plasmid nor genomic DNA from Leuc. mesenteroides subsp. cremoris 195 hybridized with the citP probe.

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Summary -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 ceIls growing on galactose increased the growth rate and decreased galactose utilization. p-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 quantities 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. Leuconostoc 1lactose 1galactose 1p-galactosidase 1galactokinase

α‐Galactosidases (α‐gal) from six strains of Leuconostoc mesenteroides subsp. mesenteroides, which were isolated from four different ecological niches, have been characterized. The enzymes have an optimum pH ranging from 5.5 to 6.4. Strain 19A possesses a pH optimum close to neutral. The optimum temperature varied with the strains, ranging from 37 to 43 °C. The Km values of the enzymes for substrate p‐nitrophenyl‐α‐D‐galactopyranoside (PNPG) varied from 2.15 to 22.70 mM. α‐Gal from strain 23A had the lowest affinity for substrate PNPG. An increase of the affinity for PNPG in the presence of 10 mM lactose was observed for strains 6M, 19A, 23A, 19M, while this higher affinity for PNPG was also observed in the presence of 10 mM galactose for strains 6M, 23A, 19M. The activation energy of the enzyme from different strains was calculated to be about 62.9–72.8 kJ/mol. Ca2+ ions have a strong inhibitive effect on the enzyme activity. Appearance of α‐gal activity band and protein profiles under the same conditions of SDS‐PAGE allowed an estimation of the apparent molecular weight of α‐gal to be at about 175,000.