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- Nilsson, Astrid, et al.
(författare)
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Environmental impacts and limitations of third-generation biobutanol : Life cycle assessment of n-butanol produced by genetically engineered cyanobacteria
- 2020
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Ingår i: Journal of Industrial Ecology. - : WILEY. - 1088-1980 .- 1530-9290. ; 24:1
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Tidskriftsartikel (refereegranskat)abstract
- Photosynthetic cyanobacteria have attracted interest as production organisms for third-generation biofuels, where sunlight and CO2 are used by microbes directly to synthesize fuel molecules. A particularly suitable biofuel is n-butanol, and there have been several laboratory reports of genetically engineered photosynthetic cyanobacteria capable of synthesizing and secreting n-butanol. This work evaluates the environmental impacts and cumulative energy demand (CED) of cyanobacteria-produced n-butanol through a cradle-to-grave consequential life cycle assessment (LCA). A hypothetical production plant in northern Sweden (area 1 ha, producing 5-85 m(3) n-butanol per year) was considered, and a range of cultivation formats and cellular productivity scenarios assessed. Depending on the scenario, greenhouse gas emissions (GHGe) ranged from 16.9 to 58.6 gCO(2)eq/MJ(BuOH) and the CED from 3.8 to 13 MJ/MJ(BuOH). Only with the assumption of a nearby paper mill to supply waste sources for heat and CO2 was the sustainability requirement of at least 60% GHGe savings compared to fossil fuels reached, though placement in northern Sweden reduced energy needed for reactor cooling. A high CED in all scenarios shows that significant metabolic engineering is necessary, such as a carbon partitioning of >90% to n-butanol, as well as improved light utilization, to begin to displace fossil fuels or even first- and second-generation bioethanol.
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| 2. |
- Shabestary, Kiyan, 1991-
(författare)
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Improving cyanobacteria productivity: From theory to assay
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Bio-based production of biochemicals and biofuels holds great promises for the transition towards a more sustainable society. With increasing levels of carbon dioxide (CO2) in the atmosphere, cyanobacteria stand apart as natural catalysts directly converting CO2 and light to product. However, current product productivities and titers do not meet the standard set by the petroleum-based industry. In particular, the solar-to-product efficiency needs to be drastically improved to make the process economically more interesting. As proof of concept, this thesis puts an emphasis on identifying metabolic limitations towards increased solar-to-product efficiency using model-guided formulation of strategies and genome-wide screening, followed by novel practical implementations. It follows previous works identifying the intracellular ATP/NADPH ratio as an important variable to balance photosynthesis, carbon fixation, product synthesis and biomass formation to ensure more performant metabolic engineering designs of photoautotrophs. In Paper I, we identified in silico growth-coupled metabolic designs linking product formation to growth to increase productivity and stability of the engineered strain. In Paper II, we found computationally and experimentally that carbon rerouting gave the best results to increase product formation. In Paper III, we used the CRISPRi system to further maximize carbon rerouting to product synthesis in growth-arrest strategies. Finally, in Paper IV, we conduct a genome-wide screening using a CRISPRi library and identified key targets to improve product synthesis, product tolerance and growth. We also demonstrate experimentally some of the strategies found in Paper I. This thesis suggests that growth-arrest production is a promising avenue to maximize the solar-to-product efficiency and asserts that systems biology tools will be needed to identify and tackle the remaining strain instability associated with those designs.
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| 3. |
- Yao, Lun, et al.
(författare)
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Pooled CRISPRi screening of the cyanobacterium Synechocystis sp PCC 6803 for enhanced industrial phenotypes
- 2020
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Ingår i: Nature Communications. - : Nature Research. - 2041-1723. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Cyanobacteria are model organisms for photosynthesis and are attractive for biotechnology applications. To aid investigation of genotype-phenotype relationships in cyanobacteria, we develop an inducible CRISPRi gene repression library in Synechocystis sp. PCC 6803, where we aim to target all genes for repression. We track the growth of all library members in multiple conditions and estimate gene fitness. The library reveals several clones with increased growth rates, and these have a common upregulation of genes related to cyclic electron flow. We challenge the library with 0.1 M L-lactate and find that repression of peroxiredoxin bcp2 increases growth rate by 49%. Transforming the library into an L-lactate-secreting Synechocystis strain and sorting top lactate producers enriches clones with sgRNAs targeting nutrient assimilation, central carbon metabolism, and cyclic electron flow. In many examples, productivity can be enhanced by repression of essential genes, which are difficult to access by transposon insertion.
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