Publications

2012
Kim, YI, Vinyard DJ, Ananyev GM, Dismukes CG, Golden SS.  2012.  Oxidized quinones signal onset of darkness directly to the cyanobacterial circadian oscillator.. Proceedings of the National Academy of Sciences of the United States of America. 109(44):17765-9. Abstract
Synchronization of the circadian clock in cyanobacteria with the day/night cycle proceeds without an obvious photoreceptor, leaving open the question of its specific mechanism. The circadian oscillator can be reconstituted in vitro, where the activities of two of its proteins, KaiA and KaiC, are affected by metabolites that reflect photosynthetic activity: KaiC phosphorylation is directly influenced by the ATP/ADP ratio, and KaiA stimulation of KaiC phosphorylation is blocked by oxidized, but not reduced, quinones. Manipulation of the ATP/ADP ratio can reset the timing of KaiC phosphorylation peaks in the reconstituted in vitro oscillator. Here, we show that pulses of oxidized quinones reset the cyanobacterial circadian clock both in vitro and in vivo. Onset of darkness causes an abrupt oxidation of the plastoquinone pool in vivo, which is in contrast to a gradual decrease in the ATP/ADP ratio that falls over the course of hours until the onset of light. Thus, these two metabolic measures of photosynthetic activity act in concert to signal both the onset and duration of darkness to the cyanobacterial clock.
Ananyev, GM, Skizim NJ, Dismukes CG.  2012.  Enhancing biological hydrogen production from cyanobacteria by removal of excreted products.. Journal of biotechnology. 162(1):97-104. Abstract
Hydrogen is produced by a [NiFe]-hydrogenase in the cyanobacterium Arthrospira (Spirulina) maxima during autofermentation of photosynthetically accumulated glycogen under dark anaerobic conditions. Herein we show that elimination of H₂ backpressure by continuous H₂ removal ("milking") can significantly increase the yield of H₂ in this strain. We show that "milking" by continuous selective consumption of H₂ using an electrochemical cell produces the maximum increase in H₂ yield (11-fold) and H₂ rate (3.4-fold), which is considerably larger than through "milking" by non-selective dilution of the biomass in media (increases H₂ yield 3.7-fold and rate 3.1-fold). Exhaustive autofermentation under electrochemical milking conditions consumes >98% of glycogen and 27.6% of biomass over 7-8 days and extracts 39% of the energy content in glycogen as H₂. Non-selective dilution stimulates H₂ production by shifting intracellular equilibria competing for NADH from excreted products and terminal electron sinks into H₂ production. Adding a mixture of the carbon fermentative products shifts the equilibria towards reactants, resulting in increased intracellular NADH and an increased H₂ yield (1.4-fold). H₂ production is sustained for a period of time up to 7days, after which the PSII activity of the cells decreases by 80-90%, but can be restored by regeneration under photoautotrophic growth.
Kolling, DR, Cox N, Ananyev GM, Pace RJ, Dismukes CG.  2012.  What are the oxidation states of manganese required to catalyze photosynthetic water oxidation? Biophysical journal. 103(2):313-22. Abstract
Photosynthetic O(2) production from water is catalyzed by a cluster of four manganese ions and a tyrosine residue that comprise the redox-active components of the water-oxidizing complex (WOC) of photosystem II (PSII) in all known oxygenic phototrophs. Knowledge of the oxidation states is indispensable for understanding the fundamental principles of catalysis by PSII and the catalytic mechanism of the WOC. Previous spectroscopic studies and redox titrations predicted the net oxidation state of the S(0) state to be (Mn(III))(3)Mn(IV). We have refined a previously developed photoassembly procedure that directly determines the number of oxidizing equivalents needed to assemble the Mn(4)Ca core of WOC during photoassembly, starting from free Mn(II) and the Mn-depleted apo-WOC complex. This experiment entails counting the number of light flashes required to produce the first O(2) molecules during photoassembly. Unlike spectroscopic methods, this process does not require reference to synthetic model complexes. We find the number of photoassembly intermediates required to reach the lowest oxidation state of the WOC, S(0), to be three, indicating a net oxidation state three equivalents above four Mn(II), formally (Mn(III))(3)Mn(II), whereas the O(2) releasing state, S(4), corresponds formally to (Mn(IV))(3)Mn(III). The results from this study have major implications for proposed mechanisms of photosynthetic water oxidation.
Skizim, NJ, Ananyev GM, Krishnan A, Dismukes CG.  2012.  Metabolic pathways for photobiological hydrogen production by nitrogenase- and hydrogenase-containing unicellular cyanobacteria Cyanothece.. The Journal of biological chemistry. 287(4):2777-86. Abstract
Current biotechnological interest in nitrogen-fixing cyanobacteria stems from their robust respiration and capacity to produce hydrogen. Here we quantify both dark- and light-induced H(2) effluxes by Cyanothece sp. Miami BG 043511 and establish their respective origins. Dark, anoxic H(2) production occurs via hydrogenase utilizing reductant from glycolytic catabolism of carbohydrates (autofermentation). Photo-H(2) is shown to occur via nitrogenase and requires illumination of PSI, whereas production of O(2) by co-illumination of PSII is inhibitory to nitrogenase above a threshold pO(2). Carbohydrate also serves as the major source of reductant for the PSI pathway mediated via nonphotochemical reduction of the plastoquinone pool by NADH dehydrogenases type-1 and type-2 (NDH-1 and NDH-2). Redirection of this reductant flux exclusively through the proton-coupled NDH-1 by inhibition of NDH-2 with flavone increases the photo-H(2) production rate by 2-fold (at the expense of the dark-H(2) rate), due to production of additional ATP (via the proton gradient). Comparison of photobiological hydrogen rates, yields, and energy conversion efficiencies reveals opportunities for improvement.
Nguyen, TA, Brescic J, Vinyard DJ, Chandrasekar T, Dismukes CG.  2012.  Identification of an oxygenic reaction center psbADC operon in the cyanobacterium Gloeobacter violaceus PCC 7421.. Molecular biology and evolution. 29(1):35-8. Abstract
Gloeobacter violaceus, the earliest diverging oxyphotobacterium (cyanobacterium) on the 16S ribosomal RNA tree, has five copies of the photosystem II psbA gene encoding the D1 reaction center protein subunit. These copies are widely distributed throughout the 4.6 Mbp genome with only one copy colocalizing with other PSII subunits, in marked contrast to all other psbA genes in all publicly available sequenced genomes. A clustering of two other psb genes around psbA3 (glr2322) is unique to Gloeobacter. We provide experimental proof for the transcription of a psbA3DC operon, encoding three of the five reaction center core subunits (D1, D2, and CP43). This is the first example of a transcribed gene cluster containing the D1/D2 or D1/D2/CP43 subunits of PSII in an oxygenic phototroph (prokaryotic or eukaryotic). Implications for the evolution of oxygenic photosynthesis are discussed.
Gardner, GP, Go Y B, Robinson DM, Smith PF, Hadermann J, Abakumov A, Greenblatt M, Dismukes CG.  2012.  Structural requirements in lithium cobalt oxides for the catalytic oxidation of water.. Angewandte Chemie (International ed. in English). 51(7):1616-9.
Burrows, EH, Bennette NB, Carrieri D, Dixon JL, Brinker A, Frada M, Bakdassabim S N, Falkowski PG, Dismukes GC.  2012.  Dynamics of Lipid Biosynthesis and Redistribution in the Marine Diatom Phaeodactylum tricornutum under Nitrate Deprivation. Bioenerg. Res. 5:876-885. Abstract
One approach to achieve continuous overproduction of lipids in microalgal “cell factories” relies upon depletion or removal of nutrients that act as competing electron sinks (e.g., nitrate and sulfate). However, this strategy can only be effective for bioenergy applications if lipid is synthesized primarily de novo (from CO2 fixation) rather than from the breakdown and interconversion of essential cellular components. In the marine diatom, Phaeodactylum tricornutum, it was determined, using 13C-bicarbonate, that cell growth in nitrate (NO 3 − )-deprived cultures resulted predominantly in de novo lipid synthesis (60 % over 3 days), and this new lipid consisted primarily of triacylglycerides (TAGs). Nearly complete preservation of 12C occurred in all previously existing TAGs in NO 3 − -deprived cultures and thus, further TAG accumulation would not be expected from inhibition of TAG lipolysis. In contrast, both high turnover and depletion of membrane lipids, phosphatidylcholines (PCs), were observed in NO 3 − -deprived cultures (both the headgroups and fatty acid chains), while less turnover was observed in NO 3 − replete cultures. Liquid chromatography-tandem mass spectrometry mass spectra and 13C labeling patterns of PC headgroups provided insight into lipid synthesis in marine diatoms, including suggestion of an internal pool of glycine betaine that feeds choline synthesis. It was also observed that 16C fatty acid chains incorporated into TAGs and PCs contained an average of 14 13C carbons, indicating substantial incorporation of 13C-bicarbonate into fatty acid chains under both nutrient states.
2011
Carrieri, D, Ananyev GM, Lenz O, Bryant DA, Dismukes CG.  2011.  Contribution of a sodium ion gradient to energy conservation during fermentation in the cyanobacterium Arthrospira (Spirulina) maxima CS-328.. Applied and environmental microbiology. 77(20):7185-94. Abstract
Sodium gradients in cyanobacteria play an important role in energy storage under photoautotrophic conditions but have not been well studied during autofermentative metabolism under the dark, anoxic conditions widely used to produce precursors to fuels. Here we demonstrate significant stress-induced acceleration of autofermentation of photosynthetically generated carbohydrates (glycogen and sugars) to form excreted organic acids, alcohols, and hydrogen gas by the halophilic, alkalophilic cyanobacterium Arthrospira (Spirulina) maxima CS-328. When suspended in potassium versus sodium phosphate buffers at the start of autofermentation to remove the sodium ion gradient, photoautotrophically grown cells catabolized more intracellular carbohydrates while producing 67% higher yields of hydrogen, acetate, and ethanol (and significant amounts of lactate) as fermentative products. A comparable acceleration of fermentative carbohydrate catabolism occurred upon dissipating the sodium gradient via addition of the sodium-channel blocker quinidine or the sodium-ionophore monensin but not upon dissipating the proton gradient with the proton-ionophore dinitrophenol (DNP). The data demonstrate that intracellular energy is stored via a sodium gradient during autofermentative metabolism and that, when this gradient is blocked, the blockage is compensated by increased energy conversion via carbohydrate catabolism.
Meuser, JE, Boyd ES, Ananyev GM, Karns D, Radakovits R, Narayana Murthy UM, Ghirardi ML, Dismukes CG, Peters JW, Posewitz MC.  2011.  Evolutionary significance of an algal gene encoding an [FeFe]-hydrogenase with F-domain homology and hydrogenase activity in Chlorella variabilis NC64A.. Planta. 234(4):829-43. Abstract
[FeFe]-hydrogenases (HYDA) link the production of molecular H(2) to anaerobic metabolism in many green algae. Similar to Chlamydomonas reinhardtii, Chlorella variabilis NC64A (Trebouxiophyceae, Chlorophyta) exhibits [FeFe]-hydrogenase (HYDA) activity during anoxia. In contrast to C. reinhardtii and other chlorophycean algae, which contain hydrogenases with only the HYDA active site (H-cluster), C. variabilis NC64A is the only known green alga containing HYDA genes encoding accessory FeS cluster-binding domains (F-cluster). cDNA sequencing confirmed the presence of F-cluster HYDA1 mRNA transcripts, and identified deviations from the in silico splicing models. We show that HYDA activity in C. variabilis NC64A is coupled to anoxic photosynthetic electron transport (PSII linked, as well as PSII-independent) and dark fermentation. We also show that the in vivo H(2)-photoproduction activity observed is as O(2) sensitive as in C. reinhardtii. The two C. variabilis NC64A HYDA sequences are similar to homologs found in more deeply branching bacteria (Thermotogales), diatoms, and heterotrophic flagellates, suggesting that an F-cluster HYDA is the ancestral enzyme in algae. Phylogenetic analysis indicates that the algal HYDA H-cluster domains are monophyletic, suggesting that they share a common origin, and evolved from a single ancestral F-cluster HYDA. Furthermore, phylogenetic reconstruction indicates that the multiple algal HYDA paralogs are the result of gene duplication events that occurred independently within each algal lineage. Collectively, comparative genomic, physiological, and phylogenetic analyses of the C. variabilis NC64A hydrogenase has provided new insights into the molecular evolution and diversity of algal [FeFe]-hydrogenases.
Dismukes, CG, McNeely K, Eng JF.  2011.  An LC-MS-based chemical and analytical method for targeted metabolite quantification in the model cyanobacterium Synechococcus sp. PCC 7002.. Analytical chemistry. 83(10):3808-16. Abstract
Herein, we detail the development of a method for the chemical isolation and tandem LC-MS/MS quantification of a targeted subset of internal metabolites from cyanobacteria. We illustrate the selection of target compounds; requirements for and optimization of mass spectral detection channels, screening, and optimization of chromatography; and development of a sampling protocol that seeks to achieve complete, representative, and stable metabolite extraction on the seconds time scale. Several key factors influencing the separation by reversed-phase ion pairing chromatography, specifically the hydrophobicity of the sample matrix and sensitivity to mobile phase acidity, are identified and resolved. We illustrate this methodology with an example from the autofermentative metabolism in the model cyanobacterium Synechococcus sp. PCC 7002, for which intracellular levels of 25 metabolites were monitored over 48 h, including intermediates in central carbon metabolism together with those involved in the cellular energy charge and redox poise. Upon removal of alternative reductant sinks (nitrate), anoxia induces autofermentation of carbohydrates with a parallel rise in the intracellular pyridine nucleotide redox poise that is specific to NAD(H) and alongside a gradual decline in the adenylate energy charge. This LC-MS/MS-based method provides for accurate time-resolved quantification of multiple metabolites in parallel, thus enabling experimental verification of the active metabolic pathways.
Dismukes, CG, McNeely K, Robinson DM, Sheats JE.  2011.  A Co4O4 "cubane" water oxidation catalyst inspired by photosynthesis.. Journal of the American Chemical Society. 133(30):11446-9. Abstract
Herein we describe the molecular Co(4)O(4) cubane complex Co(4)O(4)(OAc)(4)(py)(4) (1), which catalyzes efficient water oxidizing activity when powered by a standard photochemical oxidation source or electrochemical oxidation. The pH dependence of catalysis, the turnover frequency, and in situ monitoring of catalytic species have revealed the intrinsic capabilities of this core type. The catalytic activity of complex 1 and analogous Mn(4)O(4) cubane complexes is attributed to the cubical core topology, which is analogous to that of nature's water oxidation catalyst, a cubical CaMn(4)O(5) cluster.
Dismukes, CG, McNeely K, Xu Y, Ananyev GM, Bennette N, Bryant DA.  2011.  Synechococcus sp. strain PCC 7002 nifJ mutant lacking pyruvate:ferredoxin oxidoreductase.. Applied and environmental microbiology. 77(7):2435-44. Abstract
The nifJ gene codes for pyruvate:ferredoxin oxidoreductase (PFOR), which reduces ferredoxin during fermentative catabolism of pyruvate to acetyl-coenzyme A (acetyl-CoA). A nifJ knockout mutant was constructed that lacks one of two pathways for the oxidation of pyruvate in the cyanobacterium Synechococcus sp. strain PCC 7002. Remarkably, the photoautotrophic growth rate of this mutant increased by 20% relative to the wild-type (WT) rate under conditions of light-dark cycling. This result is attributed to an increase in the quantum yield of photosystem II (PSII) charge separation as measured by photosynthetic electron turnover efficiency determined using fast-repetition-rate fluorometry (F(v)/F(m)). During autofermentation, the excretion of acetate and lactate products by nifJ mutant cells decreased 2-fold and 1.2-fold, respectively. Although nifJ cells displayed higher in vitro hydrogenase activity than WT cells, H(2) production in vivo was 1.3-fold lower than the WT level. Inhibition of acetate-CoA ligase and pyruvate dehydrogenase complex by glycerol eliminated acetate production, with a resulting loss of reductant and a 3-fold decrease in H(2) production by nifJ cells compared to WT cells. Continuous electrochemical detection of dissolved H(2) revealed two temporally resolved phases of H(2) production during autofermentation, a minor first phase and a major second phase. The first phase was attributed to reduction of ferredoxin, because its level decreased 2-fold in nifJ cells. The second phase was attributed to glycolytic NADH production and decreased 20% in nifJ cells. Measurement of the intracellular NADH/NAD(+) ratio revealed that the reductant generated by PFOR contributing to the first phase of H(2) production was not in equilibrium with bulk NADH/NAD(+) and that the second phase corresponded to the equilibrium NADH-mediated process.
Carrieri, D, Momot D, Brasg IA, Ananyev GM, Lenz O, Bryant DA, Dismukes CG.  2011.  Boosting autofermentation rates and product yields with sodium stress cycling: Application to renewable fuel production by cyanobacteria. Appl. Environ. Microbiol.. :AEM.00975-10%Uhttp://aem.asm.org/cgi/content/abstract/AEM.00975-10v1. Abstract
Sodium concentration cycling was examined as a new strategy for redistributing carbon storage products and increasing autofermentative product yields following photosynthetic carbon fixation in the cyanobacterium Arthrospira (Spirulina) maxima. The salt-tolerant hyper-carbonate strain CS-328 was grown in a medium containing 0.24 to 1.24 M sodium, resulting in increased biosynthesis of soluble carbohydrates up to 50% of the dry weight at 1.24 M sodium. Hypoionic stress during dark anaerobic metabolism (autofermentation) was induced by resuspending filaments in low sodium (bi)carbonate buffer (0.21 M), which resulted in accelerated autofermentation rates. For cells grown in 1.24 M NaCl, the fermentative yields of acetate, ethanol and formate increase substantially to 0.75, 1.56 and 1.54 mmol/(gDW*day), respectively (36, 121, and 6-fold increases in rate relative to cells grown in 0.24 M NaCl). Catabolism of endogenous carbohydrate increased by approximately 2-fold upon hypoionic stress. For cultures grown at all salt concentrations, hydrogen was produced but its yield did not correlate with increased catabolism of soluble carbohydrates. Instead, ethanol excretion becomes a preferred route for fermentative NADH reoxidation together with intraceullar accumulation of reduced products of acetyl-CoA formation when cells are hypoionically stressed. In the absence of hypoionic stress, hydrogen production is a major beneficial pathway for NAD+ regeneration without wasting carbon intermediates such as ethanol derived from acetyl-CoA. This switch presumably improves the overall cellular economy by retaining carbon within the cell until aerobic conditions return and the acetyl unit can be used for biosynthesis or oxidized via respiration for much greater energy return.
McNeely, K, Xu Y, Ananyev GM, Bennette N, Bryant DA, Dismukes CG.  2011.  Characterization of a nifJ Mutant of Synechococcus sp. strain PCC 7002 Lacking Pyruvate:Ferredoxin Oxidoreductase. Appl. Environ. Microbiol.. :AEM.02792-10. AbstractWebsite
The nifJ gene codes for pyruvate:ferredoxin oxidoreductase, which reduces ferredoxin during fermentative catabolism of pyruvate to acetyl-CoA. A nifJ knock-out mutant was constructed that lacks one of two pathways for the oxidation of pyruvate in the cyanobacterium Synechococcus sp. strain PCC 7002. Remarkably, the photoautotrophic growth rate of this mutant increased by 20% relative to wild type (WT) under light-dark cycling. This is attributed to an increase in the quantum yield of PSII charge separation as measured by photosynthetic electron turnover efficiency using fast repetition rate fluorometry (Fv/Fm). During autofermentation the excretion of acetate and lactate products by nifJ mutant cells decreased 2-fold and 1.2-fold, respectively. Although nifJ cells displayed higher in vitro hydrogenase activity than WT, H2 production in vivo was 1.3-fold lower than WT. Inhibition of acetate-CoA ligase and pyruvate dehydrogenase complex by glycerol eliminated acetate production, with resulting loss of reductant and a 3-fold decrease in H2 production by nifJ cells compared to WT. Continuous electrochemical detection of dissolved H2 revealed two temporally resolved phases of H2 production during autofermentation, a minor first phase and a major second phase. The first phase was attributed to reduction of ferredoxin because it decreased 2-fold in nifJ cells. The second phase was attributed to glycolytic NADH production and decreased 20% in nifJ cells. Measurement of the intracellular NADH/NAD+ ratio revealed that the reductant generated by PFOR contributing to the first phase of H2 production was not in equilibrium with bulk NADH/NAD+, while the second phase corresponded to the equilibrium NADH-mediated process.
McCool, NS, Robinson DM, Sheats JE, Dismukes CG.  2011.  A Co4O4 “Cubane” Water Oxidation Catalyst Inspired by Photosynthesis. Journal of the American Chemical Society. 133:11446-11449. AbstractWebsite
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Meuser, J, Boyd E, Ananyev GM, Karns D, Radakovits R, Narayana Murthy U, Ghirardi M, Dismukes G, Peters J, Posewitz M.  2011.  Evolutionary significance of an algal gene encoding an [FeFe]-hydrogenase with F-domain homology and hydrogenase activity in <i>Chlorella variabilis</i> NC64A. Planta. :1-15.Website
Brimblecombe, R, Chen J, Wagner P, Buchhorn T, Dismukes CG, Spiccia L, Swiegers GF.  2011.  Photocatalytic oxygen evolution from non-potable water by a bioinspired molecular water oxidation catalyst. Journal of Molecular Catalysis A: Chemical. 338:1-6.Website
2010
Work, VH, Radakovits R, Jinkerson RE, Meuser JE, Elliott LG, Vinyard DJ, Laurens LML, Dismukes CG, Posewitz MC.  2010.  Increased Lipid Accumulation in the Chlamydomonas reinhardtii sta7-10 Starchless Isoamylase Mutant and Increased Carbohydrate Synthesis in Complemented Strains. Eukaryotic Cell. 9:1251-1261. AbstractWebsite
The accumulation of bioenergy carriers was assessed in two starchless mutants of Chlamydomonas reinhardtii (the sta6 [ADP-glucose pyrophosphorylase] and sta7-10 [isoamylase] mutants), a control strain (CC124), and two complemented strains of the sta7-10 mutant. The results indicate that the genetic blockage of starch synthesis in the sta6 and sta7-10 mutants increases the accumulation of lipids on a cellular basis during nitrogen deprivation relative to that in the CC124 control as determined by conversion to fatty acid methyl esters. However, this increased level of lipid accumulation is energetically insufficient to completely offset the loss of cellular starch that is synthesized by CC124 during nitrogen deprivation. We therefore investigated acetate utilization and O2 evolution to obtain further insights into the physiological adjustments utilized by the two starchless mutants in the absence of starch synthesis. The results demonstrate that both starchless mutants metabolize less acetate and have more severely attenuated levels of photosynthetic O2 evolution than CC124, indicating that a decrease in overall anabolic processes is a significant physiological response in the starchless mutants during nitrogen deprivation. Interestingly, two independent sta7-10:STA7 complemented strains exhibited significantly greater quantities of cellular starch and lipid than CC124 during acclimation to nitrogen deprivation. Moreover, the complemented strains synthesized significant quantities of starch even when cultured in nutrient-replete medium.
Dismukes, CG, Brimblecombe R, Koo A, Swiegers GF, Spiccia L.  2010.  A tandem water-splitting device based on a bio-inspired manganese catalyst.. ChemSusChem. 3(10):1146-50.
Pushkar, Y, Long X, Glatzel P, Brudvig G W, Dismukes  CG, Collins T J, Yachandra V K, Yano J, Bergmann U.  2010.  Direct Detection of Oxygen Ligation to the Mn4Ca Cluster of Photosystem II by X-ray Emission Spectroscopy. Angewandte Chemie International Edition. 49:800-803.Website
McNeely, K, Xu Y, Bennette N, Bryant DA, Dismukes CG.  2010.  Redirecting Reductant Flux into Hydrogen Production via Metabolic Engineering of Fermentative Carbon Metabolism in a Cyanobacterium. Appl. Environ. Microbiol.. 76:5032-5038. AbstractWebsite
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 ldhA 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 ldhA 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 ldhA 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 ldhA mutant is 12%. Together with the unimpaired photoautotrophic growth of the ldhA mutant, these attributes reveal that metabolic engineering is an effective strategy to enhance H2 production in AMOPs without compromising viability.
Brimblecombe, R, Koo A, Dismukes CG, Swiegers GF, Spiccia L.  2010.  Solar Driven Water Oxidation by a Bioinspired Manganese Molecular Catalyst. Journal of the American Chemical Society. 132:2892-2894. AbstractWebsite
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Brimblecombe, R, Koo A, Dismukes CG, Swiegers GF, Spiccia L.  2010.  A Tandem Water-Splitting Device Based on a Bio-inspired Manganese Catalyst. ChemSusChem. 3:1146-1150.Website