TY - JOUR
T1 - Redirecting reductant flux into hydrogen production via metabolic engineering of fermentative carbon metabolism in a cyanobacterium
AU - McNeely, Kelsey
AU - Xu, Yu
AU - Bennette, Nick
AU - Bryant, Donald A.
AU - Dismukes, G. Charles
PY - 2010/8
Y1 - 2010/8
N2 - Some aquatic microbial oxygenic photoautotrophs (AMOPs) make hydrogen (H2), a carbon-neutral, renewable product derived from water, in low yields during autofermentation (anaerobic metabolism) of intracellular carbohydrates previously stored during aerobic photosynthesis. We have constructed a mutant (the IdhA mutant) of the cyanobacterium Synechococcus sp. strain PCC 7002 lacking the enzyme for the NADH-dependent reduction of pyruvate to D-lactate, the major fermentative reductant sink in this AMOP. Both nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-mass spectrometry (LC-MS) metabolomic methods have shown that autofermentation by the IdhA mutant resulted in no D-lactate production and higher concentrations of excreted acetate, alanine, succinate, and hydrogen (up to 5-fold) compared to that by the wild type. The measured intracellular NAD(P)(H) concentrations demonstrated that the NAD (P)H/NAD (P)+ ratio increased appreciably during autofermentation in the IdhA strain; we propose this to be the principal source of the observed increase in H2 production via an NADH-dependent, bidirectional [NiFe] hydrogenase. Despite the elevated NAD(P)H/NAD(P)+ ratio, no decrease was found in the rate of anaerobic conversion of stored carbohydrates. The measured energy conversion efficiency (ECE) from biomass (as glucose equivalents) converted to hydrogen in the IdhA mutant is 12%. Together with the unimpaired photoautotrophic growth of the IdhA mutant, these attributes reveal that metabolic engineering is an effective strategy to enhance H2 production in AMOPs without compromising viability.
AB - Some aquatic microbial oxygenic photoautotrophs (AMOPs) make hydrogen (H2), a carbon-neutral, renewable product derived from water, in low yields during autofermentation (anaerobic metabolism) of intracellular carbohydrates previously stored during aerobic photosynthesis. We have constructed a mutant (the IdhA mutant) of the cyanobacterium Synechococcus sp. strain PCC 7002 lacking the enzyme for the NADH-dependent reduction of pyruvate to D-lactate, the major fermentative reductant sink in this AMOP. Both nuclear magnetic resonance (NMR) spectroscopy and liquid chromatography-mass spectrometry (LC-MS) metabolomic methods have shown that autofermentation by the IdhA mutant resulted in no D-lactate production and higher concentrations of excreted acetate, alanine, succinate, and hydrogen (up to 5-fold) compared to that by the wild type. The measured intracellular NAD(P)(H) concentrations demonstrated that the NAD (P)H/NAD (P)+ ratio increased appreciably during autofermentation in the IdhA strain; we propose this to be the principal source of the observed increase in H2 production via an NADH-dependent, bidirectional [NiFe] hydrogenase. Despite the elevated NAD(P)H/NAD(P)+ ratio, no decrease was found in the rate of anaerobic conversion of stored carbohydrates. The measured energy conversion efficiency (ECE) from biomass (as glucose equivalents) converted to hydrogen in the IdhA mutant is 12%. Together with the unimpaired photoautotrophic growth of the IdhA mutant, these attributes reveal that metabolic engineering is an effective strategy to enhance H2 production in AMOPs without compromising viability.
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U2 - 10.1128/AEM.00862-10
DO - 10.1128/AEM.00862-10
M3 - Article
C2 - 20543051
AN - SCOPUS:77955572487
SN - 0099-2240
VL - 76
SP - 5032
EP - 5038
JO - Applied and environmental microbiology
JF - Applied and environmental microbiology
IS - 15
ER -