THE PHYSIOLOGY OF LACTOCOCCUS-LACTIS SUBSP LACTIS BIOVAR DIACETYLACTIS IMMOBILIZED IN HOLLOW-FIBER BIOREACTORS - GLUCOSE, LACTOSE AND CITRATE METABOLISM AT HIGH CELL DENSITIES
Mr. Smith et al., THE PHYSIOLOGY OF LACTOCOCCUS-LACTIS SUBSP LACTIS BIOVAR DIACETYLACTIS IMMOBILIZED IN HOLLOW-FIBER BIOREACTORS - GLUCOSE, LACTOSE AND CITRATE METABOLISM AT HIGH CELL DENSITIES, Applied microbiology and biotechnology, 39(1), 1993, pp. 94-98
Lactococcus lactis subsp. lactis biovar. diacetylactis was selected to
study the physiological influences of immobilization and growth to hi
gh cell densities. Cells were cultivated on glucose or lactose medium
in the presence and absence of citrate. With excess glucose the cells
produced mainly lactate as the fermentation product (homofermentative)
providing that not all of the substrate was consumed. The population
so cultivated was exposed to extreme gradients of pH and lactate conce
ntrations. When the glucose concentration was reduced the population s
howed a mixed product profile with half of the glucose being fermented
to lactate, the remainder to formate, acetate, ethanol and 2,3-butane
diol. Inclusion of citrate in the medium shifted the population to hom
ofermentation, with respect to the amount of glucose or lactose consum
ed. The citrate was metabolized via the pyruvate-formate lyase and alp
ha-acetolactate synthase routes. The pH of the medium was shown to str
ongly influence the product profile from citrate, presumably by affect
ing the activity of the key enzymes of pyruvate metabolism. The lactoc
occi immobilized at high cell densities show product profiles typical
of carbohydrate limitation at low dilution rates.