Glucose metabolism and internal pH of Lactococcus lactis subsp. lactis cells utilizing NMR spectroscopy

The metabolism of glucose was studied in Lactococcus lactis subsp. CNRZ 125 by 13C NMR. The initial rate of glucose utilization was higher for exponential phase cells than for stationary phase cells [150 vs 85 nmol g (dry wt)-1 s -1]. 31P NMR was used to determine changes in glycolytic phosphorylated intermediates (fructose-1,6-diphosphate, dihydroxyacetone phosphate and phosphoglycerate). The internal pHs of L. lactis subsp. lactis CNRZ 141 and CNRZ 125 were also measured by 31P NMR as a function of the external pH during growth. When the external pH was 6.8, the internal pHs of strain CNRZ 141 and CNRZ 125 were similar, 7.4. After the external pH had decreased to 5.5, the internal pH of strain CNRZ 141 had declined by 0.6 unit, whereas that of strain CNRZ 125 had decreased by only 0.2 unit of pH.