Improving photosynthesis and metabolic networks for the competitive production of phototroph-derived biofuels

Work, Victoria H.; D’Adamo, Sarah; Radakovits, Randor; Jinkerson, Robert E.; Posewitz, Matthew C.

doi:10.1016/j.copbio.2011.11.022

Cited by 78 publications

(34 citation statements)

References 66 publications

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“…There are a number of factors, however, that determine overall rates of biomass accumulation at the cellular level. Some of these factors include: the absorption spectrum of the photosynthetic pigments, the optical cross-section of the light-harvesting apparatus, energy transfer efficiency, enzyme rate kinetics, the numbers and concentrations of energy transfer complexes (electron transfer chains) and enzyme catalytic sites, substrate concentrations, metabolite flux rates, metabolic compartmentalization and feedback control, respiration rates, and the partitioning of reduced carbon between new cell growth and division and energy storage [26-28]. …”

Section: Introductionmentioning

confidence: 99%

Comparative energetics and kinetics of autotrophic lipid and starch metabolism in chlorophytic microalgae: implications for biomass and biofuel production

Subramanian

Barry

Pieris

et al. 2013

Biotechnol Biofuels

117

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Due to the growing need to provide alternatives to fossil fuels as efficiently, economically, and sustainably as possible there has been growing interest in improved biofuel production systems. Biofuels produced from microalgae are a particularly attractive option since microalgae have production potentials that exceed the best terrestrial crops by 2 to 10-fold. In addition, autotrophically grown microalgae can capture CO2 from point sources reducing direct atmospheric greenhouse gas emissions. The enhanced biomass production potential of algae is attributed in part to the fact that every cell is photosynthetic. Regardless, overall biological energy capture, conversion, and storage in microalgae are inefficient with less than 8% conversion of solar into chemical energy achieved. In this review, we examine the thermodynamic and kinetic constraints associated with the autotrophic conversion of inorganic carbon into storage carbohydrate and oil, the dominant energy storage products in Chlorophytic microalgae. We discuss how thermodynamic restrictions including the loss of fixed carbon during acetyl CoA synthesis reduce the efficiency of carbon accumulation in lipids. In addition, kinetic limitations, such as the coupling of proton to electron transfer during plastoquinone reduction and oxidation and the slow rates of CO2 fixation by Rubisco reduce photosynthetic efficiency. In some cases, these kinetic limitations have been overcome by massive increases in the numbers of effective catalytic sites, e.g. the high Rubisco levels (mM) in chloroplasts. But in other cases, including the slow rate of plastoquinol oxidation, there has been no compensatory increase in the abundance of catalytically limiting protein complexes. Significantly, we show that the energetic requirements for producing oil and starch relative to the recoverable energy stored in these molecules are very similar on a per carbon basis. Presently, the overall rates of starch and lipid synthesis in microalgae are very poorly characterized. Increased understanding of the kinetic constraints of lipid and starch synthesis, accumulation and turnover would facilitate the design of improved biomass production systems.

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Section: Introductionmentioning

confidence: 99%

Comparative energetics and kinetics of autotrophic lipid and starch metabolism in chlorophytic microalgae: implications for biomass and biofuel production

Subramanian

Barry

Pieris

et al. 2013

Biotechnol Biofuels

117

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“…Research on lipid metabolism in microalgae has flourished in recent years due to their potential as a rich source of v-3 fatty acids (Guschina and Harwood, 2006;Khozin-Goldberg et al, 2011) and as a feedstock for biodiesel (Hu et al, 2008b;Rosenberg et al, 2008;Beer et al, 2009;Radakovits et al, 2010;Wijffels and Barbosa, 2010;Merchant et al, 2012;Work et al, 2012). Oils produced by microalgae resemble that of plants (Hu et al, 2008b), with the exception that they contain higher proportions of polyunsaturated fatty acid (PUFA) species (Harwood and Guschina, 2009).…”

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confidence: 99%

The Green Microalga Chlamydomonas reinhardtii Has a Single -3 Fatty Acid Desaturase That Localizes to the Chloroplast and Impacts Both Plastidic and Extraplastidic Membrane Lipids

et al. 2013

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The v-3 polyunsaturated fatty acids account for more than 50% of total fatty acids in the green microalga Chlamydomonas reinhardtii, where they are present in both plastidic and extraplastidic membranes. In an effort to elucidate the lipid desaturation pathways in this model alga, a mutant with more than 65% reduction in total v-3 fatty acids was isolated by screening an insertional mutant library using gas chromatography-based analysis of total fatty acids of cell pellets. Molecular genetics analyses revealed the insertion of a TOC1 transposon 113 bp upstream of the ATG start codon of a putative v-3 desaturase (CrFAD7; locus Cre01.g038600). Nuclear genetic complementation of crfad7 using genomic DNA containing CrFAD7 restored the wild-type fatty acid profile. Under standard growth conditions, the mutant is indistinguishable from the wild type except for the fatty acid difference, but when exposed to short-term heat stress, its photosynthesis activity is more thermotolerant than the wild type. A comparative lipidomic analysis of the crfad7 mutant and the wild type revealed reductions in all v-3 fatty acid-containing plastidic and extraplastidic glycerolipid molecular species. CrFAD7 was localized to the plastid by immunofluorescence in situ hybridization. Transformation of the crfad7 plastidial genome with a codon-optimized CrFAD7 restored the v-3 fatty acid content of both plastidic and extraplastidic lipids. These results show that CrFAD7 is the only v-3 fatty acid desaturase expressed in C. reinhardtii, and we discuss possible mechanisms of how a plastid-located desaturase may impact the v-3 fatty acid content of extraplastidic lipids.

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“…Along these lines, overexpression of PEPc in Vicia narbonensis seedlings resulted in increased C and N content [56]. Increasing photosynthetic production by bioengineering crops is not only important for increased carbon sequestration [57] and biofuel production [58], but may also provide enhanced NUE as a result. Transgenic lines with increased photosynthetic capacity should therefore be evaluated in terms of nitrogen use efficiency as well, and vice-versa.…”

Section: Discussionmentioning

confidence: 99%

Understanding Plant Nitrogen Metabolism through Metabolomics and Computational Approaches

Beatty

Klein

Fischer

et al. 2016

Plants

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A comprehensive understanding of plant metabolism could provide a direct mechanism for improving nitrogen use efficiency (NUE) in crops. One of the major barriers to achieving this outcome is our poor understanding of the complex metabolic networks, physiological factors, and signaling mechanisms that affect NUE in agricultural settings. However, an exciting collection of computational and experimental approaches has begun to elucidate whole-plant nitrogen usage and provides an avenue for connecting nitrogen-related phenotypes to genes. Herein, we describe how metabolomics, computational models of metabolism, and flux balance analysis have been harnessed to advance our understanding of plant nitrogen metabolism. We introduce a model describing the complex flow of nitrogen through crops in a real-world agricultural setting and describe how experimental metabolomics data, such as isotope labeling rates and analyses of nutrient uptake, can be used to refine these models. In summary, the metabolomics/computational approach offers an exciting mechanism for understanding NUE that may ultimately lead to more effective crop management and engineered plants with higher yields.

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Improving photosynthesis and metabolic networks for the competitive production of phototroph-derived biofuels

Cited by 78 publications

References 66 publications

Comparative energetics and kinetics of autotrophic lipid and starch metabolism in chlorophytic microalgae: implications for biomass and biofuel production

Comparative energetics and kinetics of autotrophic lipid and starch metabolism in chlorophytic microalgae: implications for biomass and biofuel production

The Green Microalga Chlamydomonas reinhardtii Has a Single -3 Fatty Acid Desaturase That Localizes to the Chloroplast and Impacts Both Plastidic and Extraplastidic Membrane Lipids

Understanding Plant Nitrogen Metabolism through Metabolomics and Computational Approaches

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