Affiliation:
1. Department of Biotechnology, Technical University of Denmark, Building 223, 2800 Lyngby, 2 and Christian Hansen's Laboratorium Danmark A/S, 2970 Hørsholm, Denmark
Abstract
Fructose transport in lactococci is mediated by two phosphotransferase systems (PTS). The constitutive mannose PTS has a broad specificity and may be used for uptake of fructose with a fructose saturation constant (
K
Fru
) of 0.89 mM, giving intracellular fructose 6-phosphate. The inducible fructose PTS has a very small saturation constant (
K
Fru
, <17 μM), and the fructose 1-phosphate produced enters the Embden-Meyerhof-Parnas (EMP) pathway as fructose 1,6-diphosphate. Growth in batch cultures of
Lactococcus lactis
subsp.
cremoris
FD1 in a yeast extract medium with fructose as the only sugar is poor both with respect to specific growth rate and biomass yield, whereas the specific lactic acid production rate is higher than those in similar fermentations on other sugars metabolized via the EMP pathway, e.g., glucose. In fructose-limited chemostat cultures, the biomass concentration exhibits a strong correlation with the dilution rate, and starting a continuous culture at the end of a batch fermentation leads to large and persistent oscillations in the biomass concentration and specific lactic acid production rate. Two proposed mechanisms underlying this strange growth pattern follow. (i) Fructose transported via the fructose PTS cannot be converted into essential biomass precursors (glucose 6-phosphate or fructose 6-phosphate), because
L. lactis
subsp.
cremoris
FD1 is devoid of fructose 1,6-diphosphatase activity. (ii) The fructose PTS apparently produces a metabolite (presumably fructose 1-phosphate) which exerts catabolite repression of both mannose PTS and lactose PTS. Since the repressed mannose PTS and lactose PTS are shown to have identical maximum molar transport rates, the results indicate that it is the general PTS proteins which are repressed.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
19 articles.
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