Metabolic flux response to phosphoglucose isomerase knock-out in Escherichia coli and impact of overexpression of the soluble transhydrogenase UdhA

Abstract

Blocking glycolytic breakdown of glucose by inactivation of phosphoglucose isomerase (Pgi) in Escherichia coli led to a greatly reduced maximum specific growth rate. Examination of the operational catabolic pathways and their flux ratios using [U-13 C 6 ]glucose-labeling experiments and metabolic flux ratio analysis provide evidence for the pentose phosphate (PP) pathway as the primary route of glucose catabolism in the knock-out mutant. The resulting extensive flux through the PP pathway disturbs apparently the reducing power balance, since overexpression of the recently identified soluble transhydrogenase UdhA improves significantly the growth rate of the Pgi mutant. The presented results provide first evidence that UdhA restores the cellular redox balance by catalyzing electron transfer from NADPH to NADH. ß

An in silico re-design of the metabolism in Thermotoga maritima for increased biohydrogen production

“…This finding is in agreement with experiments performed with a glucose-6-phosphate isomerase (PGI) knockout E. coli strain, which metabolized glucose through the OPP and exhibited a reduced growth rate [61]. This phenotype was explained by the lack of an efficient NADP þ regeneration system [61]. In order to test if the reduced growth rate driven by the OPP was due to the lack of a NADP þ regeneration system, we decided to include a non-native NADPH-dependent hydrogenase reaction into the model [62].…”

“…This finding is in line with the aforementioned E. coli, study [61] and suggests that a lack of reactions consuming NADPH hampers the flow through the OPP. We therefore hypothesize that the inclusion of a non-native reaction connecting the NADPH and NADH/ ferredoxin pools could increase the flux across the OPP and thus, could increase the H 2 yields.…”

“…2CeD). This finding is in agreement with experiments performed with a glucose-6-phosphate isomerase (PGI) knockout E. coli strain, which metabolized glucose through the OPP and exhibited a reduced growth rate [61]. This phenotype was explained by the lack of an efficient NADP þ regeneration system [61].…”

“…For instance, E. coli's pgi knockout mutant has been described to metabolize glucose mainly through the OPP, which introduced a redox imbalance due to excess NADPH leading to reduced growth compared to the wild-type [61]. It is interesting to note that over-expressing the soluble UdhA transhydrogenase improved the growth rate of this mutant significantly [61].…”

“…For instance, E. coli's pgi knockout mutant has been described to metabolize glucose mainly through the OPP, which introduced a redox imbalance due to excess NADPH leading to reduced growth compared to the wild-type [61]. It is interesting to note that over-expressing the soluble UdhA transhydrogenase improved the growth rate of this mutant significantly [61]. Furthermore, recurrent mutations enhancing the activity of the transhydrogenase were observed in strains isolated from adaptive evolution experiments performed on the E. coli pgi knockout strains as well as decreased acetate excretion [69].…”