The las enzymes control pyruvate metabolism in Lactococcus lactis during growth on maltose

Abstract

The fermentation pattern of Lactococcus lactis with altered activities of the las enzymes was examined on maltose. The wild type converted 65% of the maltose to mixed acids. An increase in phosphofructokinase or lactate dehydrogenase expression shifted the fermentation towards homolactic fermentation, and with a high level of expression of the las operon the fermentation was homolactic.

FIG. 1.

Simplified overview of glycolysis and its regulation by FBP and the triose phosphates dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (GAP). Positive regulation by FBP of LDH (19) is indicated by a plus sign, and negative regulation by the triose phosphates of PFL (14) is indicated by a division sign. TPI, triose phosphate isomerase; Acetyl-CoA, acetyl coenzyme A.

FIG. 2.

Metabolic fluxes for strains with modulated PFK, PYK, LDH, and las activities. The maltose, lactate, formate, and acetate fluxes are shown. The flux control coefficients (FCC) for the different fluxes are also shown. The standard deviations, indicated by error bars, are based on measurements for at least two individual cultures.

FIG. 3.

Specific growth rate, calculated ATP flux, and intracellular[ATP]/[ADP] ratio as a function of relative las activity. The standard deviations, indicated by error bars, are based on measurements for at least two individual cultures.