Open AccessPyruvate flux distribution in NADH‐oxidase‐overproducing Lactococcus lactis strain as a function of culture conditions
Author(s) -
Lopez de Felipe Felix,
Hugenholtz Jeroen
Publication year - 1999
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.1999.tb08763.x
Subject(s) - acetoin , lactococcus lactis , overproduction , biochemistry , fermentation , pyruvate dehydrogenase complex , flux (metallurgy) , chemistry , oxidase test , pyruvate decarboxylation , biology , enzyme , lactic acid , bacteria , genetics , organic chemistry
The influence of growth conditions on product formation from glucose by Lactococcus lactis strain NZ9800 engineered for NADH‐oxidase overproduction was examined. In aerobic batch cultures, a large production of acetoin and diacetyl was found at acidic pH under pH‐unregulated conditions. However, pyruvate flux was mainly driven towards lactate production when these cells were grown under strictly pH‐controlled conditions. A decreased NADH‐oxidase overproduction accompanied the homolactic fermentation, suggesting that the cellular energy was used with preference to maintain cellular homeostasis rather than for NADH‐oxidase overproduction. The end product formation and NADH‐oxidase activity were also studied in cells grown in aerobic continuous cultures under acidic conditions. A homoacetic type of fermentation as well as a low NADH‐oxidase overproduction were observed at low dilution rates. NADH‐oxidase was efficiently overproduced as the dilution rate was increased and consequently metabolic flux through lactate dehydrogenase drastically decreased. Under these conditions the flux limitation via pyruvate dehydrogenase was relieved and this enzymatic complex accommodated most of the pyruvate flux. Pyruvate was also significantly converted to acetoin and diacetyl via α‐acetolactate synthase. At higher dilution rates, acetate production declined and the cultures turned to mixed‐acid fermentation. These results suggest that the need to maintain the cellular homeostasis influenced NADH‐oxidase overproduction and consequently the end product formation from glucose in these engineered strains.