In Vivo NMR Analysis of the Influence of Pyruvate Decarboxylase and Alcohol Dehydrogenase of Zymomonas mobi'lis on the Anaerobic Metabolism of Escherichia coli

DÍAZ RICCI, JUAN C.; HITZMANN, BERND; BAILEY, JAMES E.

Biotecnology Progress

Wiley

Año: 1991 vol. 7 p. 305 - 310

Phosphorus-31 NMR studies of Escherichia coli expressingcloned pyruvate decarboxylase(pdc) and alcoholdehydrogenase (adh) genes from Zymomonas mobilis revealedsignificant changes in the concentration ofintracellular metabolites. The intracellularconcentrations of phosphate, sugarphosphates, NAD(H), NTP, NDP, andUDPG ofthe strain HBlOl expressing pdc, adh, or both genes were analyzed at quasi steady stateduring the anaerobic catabolism of glucose.The evolution of the intracellular pH andextracellular pH during glucose consumptionshowed a constant value of DpH equalto0.2pH unit that did not depend on the expression of the Zymomonas genes. Thestrainsexpressing PDC only exhibited greatestchanges in intracellular composition withsignificantly decreased inorganicphosphate, NAD(H), NTP, and UDPG and significantlyincreased sugar phosphates. Analysis of thefermentation products during the NMRexperiments provided further informationabout the physiological changes observed inthe cells. Two plasmid effects on the hostmetabolism are reported, one induced by theplasmid utilized ascontrol (pUCl9), and the otherinduced by the expression of the petoperon. In both cases an enhancement of theglucose uptake rate was observed. Althoughthe plasmid carrying adh induces a rapidmetabolic inhibition, the expression of pdcdoes not. The expression of pdc and adh together showed a physiological enhancementthat is attributable not to effects onexternal pH but rather to the effect of the switchin pathways frommixed acid to ethanol fermentation..