Effect of Vitreoscilla hemoglobin dosage on microaerobic Escherichia coli carbon and energy metabolism
The amt. of Vitreoscilla Hb (VHb) expression was modulated over a broad range with an isopropyl-beta-D-thiogalactopyranoside- (IPTG)- inducible plasmid, and the consequences on microaerobic Escherichia coli physiol. were examd. in glucose fed-batch cultivations. The effect of IPTG induction on growth under oxygen-limited conditions was most visible during late fed-batch phase where the final cell d. increased initially linearly with increasing VHb concns., ultimately satg. at a 2.7-fold increase over the VHb-neg. (VHb-) control. During the same growth phase, the specific excretions of fermn. byproducts, acetate, ethanol, formate, lactate, and succinate from the culture expressing the highest amt. of VHb were reduced by 25%, 49%, 68%, 72%, and 50%, resp., relative to the VHb- control. During the exponential growth phase, VHb exerted a pos. but smaller control on growth rate, growth yield, and respiration. Varying the amt. of VHb from 0 to 3.8 micro mol/g dry cell wt. (DCW) increased the specific growth rate, the growth yield, and the oxygen consumption rate by 33%, 35%, and 60%, resp. Increasing VHb concn. to 3.8 micro mol/g DCW suppressed the rate of carbon dioxide evolution in the exponential phase by 30%. A metabolic flux distribution anal. incorporating data from these cultivations discloses that VHb+ cells direct a larger fraction of glucose toward the pentose phosphate pathway and a smaller fraction of carbon through the tricarboxylic acid cycle from acetyl CoA. The overall NAD [NAD(P)H] flux balance indicates that VHb-expressing cells generate a net NADH flux by the NADH/NADPH transhydrogenase while the VHb- cells yield a net NADPH flux under the same growth conditions. Flux distribution anal. also reveals that VHb+ cells have a smaller ATP synthesis rate from substrate-level phosphorylation but a larger overall ATP prodn. rate under microaerobic conditions. The thermodn. efficiency of growth, based on reducing equiv. generated per unit of biomass produced, is greater for VHb+ cells. [on SciFinder (R)]
10-2 FIELD Section Title:Microbial, Algal, and Fungal Biochemistry
Inst. Biotechnology,ETH,Zurich,Switz. FIELD URL:
written in English.
Record created on 2007-01-11, modified on 2016-08-08