Elizabeth H Burrows

Oregon State University, Corvallis, OR, United States

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Publications (6)12.3 Total impact

  • Elizabeth H Burrows, Frank W R Chaplen, Roger L Ely
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    ABSTRACT: One factor limiting biosolar hydrogen (H(2)) production from cyanobacteria is electron availability to the hydrogenase enzyme. In order to optimize 24-h H(2) production this study used Response Surface Methodology and Q2, an optimization algorithm, to investigate the effects of five inhibitors of the photosynthetic and respiratory electron transport chains of Synechocystis sp. PCC 6803. Over 3 days of diurnal light/dark cycling, with the optimized combination of 9.4 mM KCN (3.1 μmol 10(10) cells(-1)) and 1.5 mM malonate (0.5 μmol 10(10) cells(-1)) the H(2) production was 30-fold higher, in EHB-1 media previously optimized for nitrogen (N), sulfur (S), and carbon (C) concentrations (Burrows et al., 2008). In addition, glycogen concentration was measured over 24 h with two light/dark cycling regimes in both standard BG-11 and EHB-1 media. The results suggest that electron flow as well as glycogen accumulation should be optimized in systems engineered for maximal H(2) output.
    Bioresource Technology 10/2010; 102(3):3062-70. · 4.75 Impact Factor
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    Proceedings of the Twenty-Fourth AAAI Conference on Artificial Intelligence, AAAI 2010, Atlanta, Georgia, USA, July 11-15, 2010; 01/2010
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    ABSTRACT: The nitrogen (N) concentration and pH of culture media were optimized for increased fermentative hydrogen (H(2)) production from the cyanobacterium, Synechocystis sp. PCC 6803. The optimization was conducted using two procedures, response surface methodology (RSM), which is commonly used, and a memory-based machine learning algorithm, Q2, which has not been used previously in biotechnology applications. Both RSM and Q2 were successful in predicting optimum conditions that yielded higher H(2) than the media reported by Burrows et al., Int J Hydrogen Energy. 2008;33:6092-6099 optimized for N, S, and C (called EHB-1 media hereafter), which itself yielded almost 150 times more H(2) than Synechocystis sp. PCC 6803 grown on sulfur-free BG-11 media. RSM predicted an optimum N concentration of 0.63 mM and pH of 7.77, which yielded 1.70 times more H(2) than EHB-1 media when normalized to chlorophyll concentration (0.68 +/- 0.43 micromol H(2) mg Chl(-1) h(-1)) and 1.35 times more when normalized to optical density (1.62 +/- 0.09 nmol H(2) OD(730) (-1) h(-1)). Q2 predicted an optimum of 0.36 mM N and pH of 7.88, which yielded 1.94 and 1.27 times more H(2) than EHB-1 media when normalized to chlorophyll concentration (0.77 +/- 0.44 micromol H(2) mg Chl(-1) h(-1)) and optical density (1.53 +/- 0.07 nmol H(2) OD(730) (-1) h(-1)), respectively. Both optimization methods have unique benefits and drawbacks that are identified and discussed in this study.
    Biotechnology Progress 08/2009; 25(4):1009-17. · 1.85 Impact Factor
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    Paul S Schrader, Elizabeth H Burrows, Roger L Ely
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    ABSTRACT: This paper describes a screening assay, compatible with high-throughput bioprospecting or molecular biology methods, for assessing biological hydrogen (H2) production. While the assay is adaptable to various physical configurations, we describe its use in a 96-well, microtiter plate format with a lower plate containing H2-producing cyanobacteria strains and controls and an upper, membrane-bottom plate containing a color indicator and a catalyst. H2 produced by cells in the lower plate diffuses through the membrane into the upper plate, causing a color change that can be quantified with a microplate reader. The assay is reproducible, semiquantitative, sensitive down to at least 20 nmol of H2, and largely unaffected by oxygen, carbon dioxide, or volatile fatty acids at levels appropriate to biological systems.
    Analytical Chemistry 07/2008; 80(11):4014-9. · 5.70 Impact Factor
  • Elizabeth H. Burrows, Frank W.R. Chaplen, Roger L. Ely
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    ABSTRACT: By optimizing concentrations of key nutrients in the media of Synechocystis sp. PCC 6803, we achieved nearly 150-fold greater photofermentative hydrogen (H2) production than was achieved by analogous, sulfur-deprived cultures, which are well known to produce much more H2 than cultures grown on complete media. This was associated with a 44-fold increase in glycogen concentration. Using response surface methodology to determine optimum conditions, we found that, instead of completely starving cells of sulfur or another essential nutrient, the highest H2 production (0.81 ± 0.36 μmol H2 mg Chl−1 h−1) occurred with 0.52 mM NH4+, 20.1 μM SO42−, and 46 mM HCO3−. H2 profiling experiments provided initial screening of NH4+, HCO3−, SO42−, and PO43− concentrations and identified the significant variables in H2 production to be NH4+, SO42−, and the interactions of both NH4+ and SO42− with HCO3−. Our results indicate that optimized amounts of nitrogen and sulfur in the nutrient media are superior to total deprivation of these nutrients for H2 production.
    International Journal of Hydrogen Energy. 01/2008;
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    Elizabeth H. Burrows
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    ABSTRACT: Graduation date: 2009 Many conditions affecting hydrogen (H₂) production by the cyanobacterium, Synechocystis sp. PCC 6803, were optimized to yield maximum H₂ accumulation. Biological H₂ production from photosynthetic species is a promising form of renewable energy since an abundant supply of sunlight hits the Earth every day, and photosynthetic bacteria can harness this solar energy and efficiently split water to produce H₂ in a safe, clean manner. The H₂ could then be used in fuel cells in a closed cycle, with water and heat as the only byproducts. There are many techniques currently in development to maximize H₂ production. We chose to use statistical optimization procedures to identify the factors which have the greatest impact on H₂ production, and simultaneously optimize them. Initially we optimized concentrations of NH₄⁺, HCO₃⁻, and SO₄²⁻, and achieved a 148-fold increase in H₂ production over sulfur deprived cultures, which have been shown to produce more H₂ than cultures grown on complete BG-11 media. With 0.52 mM NH₄⁺, 20.1 μM SO₄²⁻, and 46 mM HCO₃⁻, 0.81±0.36 μmol H₂ mg Chl⁻¹ h⁻¹ was obtained. This increase was associated with a 44-fold increase in glycogen concentration over cultures grown on BG-11. Glycogen breakdown provides substrate to the hydrogenase enzyme under dark, anaerobic conditions. Since interaction effects are strong, we then optimized pH and NH₄⁺ simultaneously, and achieved another 1.94-fold increase over the previously optimized media. This was achieved with an advanced optimization algorithm, which had never been applied to biotechnological applications. Both of these increases in H₂ production were accomplished under optimal glycogen accumulation conditions, which include acclimation to the media formulation over an extended light period, followed by immediate anaerobic, dark fermentative conditions. In an additional study we explored 24-hour H₂ production under natural, diurnal light/dark cycling, and examined glycogen accumulation dynamics as well as electron availability to the hydrogenase. Electron availability was manipulated by exposing the cultures to various inhibitors of enzymes in the photosynthetic and respiratory electron transport chains. Over 3 days, with 9.4 mM KCN and 1.5 mM malonate in the previously optimized media we were able to increase H2 production 30-fold over standard BG-11 without inhibitors.

Publication Stats

39 Citations
61 Downloads
440 Views
12.30 Total Impact Points

Institutions

  • 2008–2010
    • Oregon State University
      • Department of Biological and Ecological Engineering
      Corvallis, OR, United States
    • Yale University
      New Haven, Connecticut, United States