Abstract
Cyanobacteria have attracted much attention as hosts to recycle CO
2
into valuable chemicals. Although cyanobacteria have been engineered to produce various compounds, production ...efficiencies are too low for commercialization. Here we engineer the carbon metabolism of
Synechococcus elongatus
PCC 7942 to improve glucose utilization, enhance CO
2
fixation and increase chemical production. We introduce modifications in glycolytic pathways and the Calvin Benson cycle to increase carbon flux and redirect it towards carbon fixation. The engineered strain efficiently uses both CO
2
and glucose, and produces 12.6 g l
−1
of 2,3-butanediol with a rate of 1.1 g l
−1
d
−1
under continuous light conditions. Removal of native regulation enables carbon fixation and 2,3-butanediol production in the absence of light. This represents a significant step towards industrial viability and an excellent example of carbon metabolism plasticity.
Global climate change has stimulated efforts to reduce CO2 emissions. One approach to addressing this problem is to recycle CO2 directly into fuels or chemicals using photosynthesis. Here we ...genetically engineered Synechococcus elongatus PCC7942 to produce isobutyraldehyde and isobutanol directly from CO2 and increased productivity by overexpression of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco). Isobutyraldehyde is a precursor for the synthesis of other chemicals, and isobutanol can be used as a gasoline substitute. The high vapor pressure of isobutyraldehyde allows in situ product recovery and reduces product toxicity. The engineered strain remained active for 8 d and produced isobutyraldehyde at a higher rate than those reported for ethanol, hydrogen or lipid production by cyanobacteria or algae. These results underscore the promise of direct bioconversion of CO2 into fuels and chemicals, which bypasses the need for deconstruction of biomass.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Global energy and environmental problems have stimulated increased efforts towards synthesizing biofuels from renewable resources. Compared to the traditional biofuel, ethanol, higher alcohols offer ...advantages as gasoline substitutes because of their higher energy density and lower hygroscopicity. In addition, branched-chain alcohols have higher octane numbers compared with their straight-chain counterparts. However, these alcohols cannot be synthesized economically using native organisms. Here we present a metabolic engineering approach using Escherichia coli to produce higher alcohols including isobutanol, 1-butanol, 2-methyl-1-butanol, 3-methyl-1-butanol and 2-phenylethanol from glucose, a renewable carbon source. This strategy uses the host's highly active amino acid biosynthetic pathway and diverts its 2-keto acid intermediates for alcohol synthesis. In particular, we have achieved high-yield, high-specificity production of isobutanol from glucose. The strategy enables the exploration of biofuels beyond those naturally accumulated to high quantities in microbial fermentation.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Display omitted
•Photomixotrophic production of biofuels and plastic precursors.•Novel carbon utilization to improve cyanobacterial chemical production.•Metabolic engineering techniques to improve ...extracellular carbon uptake and use.•Methods of increasing CO2 fixation to improve cyanobacterial chemical production.
The current global dependence on fossil fuels for both energy and chemical production has spurred concerns regarding long-term resource security and environmental detriments resulting from increased CO2 levels. Through the installation of exogenous metabolic pathways, engineered cyanobacteria strains can directly fix CO2 into industrially relevant chemicals currently produced from petroleum. This review highlights some of the studies that have successfully implemented photomixotrophic conditions to increase cyanobacterial chemical production. Supplementation with fixed carbon sources provides additional carbon building blocks and energy to enhance production and occasionally aid in growth. Photomixotrophic production has increased titers up to 5-fold over traditional autotrophic conditions, demonstrating promising applications for future commercialization.
Global energy and environmental problems have stimulated increasing efforts toward synthesizing liquid biofuels as transportation energy. Compared to the traditional biofuel, ethanol, advanced ...biofuels should offer advantages such as higher energy density, lower hygroscopicity, lower vapor pressure, and compatibility with existing transportation infrastructure. However, these fuels are not synthesized economically using native organisms. Metabolic engineering offers an alternative approach in which synthetic pathways are engineered into user-friendly hosts for the production of these fuel molecules. These hosts could be readily manipulated to improve the production efficiency. This review summarizes recent progress in the engineering of Escherichia coli to produce advanced biofuels.
Biofuels synthesized from renewable resources are of increasing interest because of global energy and environmental problems. We have previously demonstrated production of higher alcohols from ...Escherichia coli using a 2-keto acid-based pathway. Here, we took advantage of the growth phenotype associated with 2-keto acid deficiency to construct a hyperproducer of 1-propanol and 1-butanol by evolving citramalate synthase (CimA) from Methanococcus jannaschii. This new pathway, which directly converts pyruvate to 2-ketobutyrate, bypasses threonine biosynthesis and represents the shortest keto acid-mediated pathway for producing 1-propanol and 1-butanol from glucose. Directed evolution of CimA enhanced the specific activity over a wide temperature range (30 to 70°C). The best CimA variant was found to be insensitive to feedback inhibition by isoleucine in addition to the improved activity. This CimA variant enabled 9- and 22-fold higher production levels of 1-propanol and 1-butanol, respectively, compared to the strain expressing the wild-type CimA. This work demonstrates (i) the first production of 1-propanol and 1-butanol using the citramalate pathway and (ii) the benefit of the 2-keto acid pathway that enables a growth-based evolutionary strategy to improve the production of non-growth-related products.
Conversion of CO₂ for the synthesis of chemicals by photosynthetic organisms is an attractive target for establishing independence from fossil reserves. However, synthetic pathway construction in ...cyanobacteria is still in its infancy compared with model fermentative organisms. Here we systematically developed the 2,3-butanediol (23BD) biosynthetic pathway in Synechococcus elongatus PCC7942 as a model system to establish design methods for efficient exogenous chemical production in cyanobacteria. We identified 23BD as a target chemical with low host toxicity, and designed an oxygen-insensitive, cofactor-matched biosynthetic pathway coupled with irreversible enzymatic steps to create a driving force toward the target. Production of 23BD from CO₂ reached 2.38 g/L, which is a significant increase for chemical production from exogenous pathways in cyanobacteria. This work demonstrates that developing strong design methods can continue to increase chemical production in cyanobacteria.
Abstract
Atmospheric CO2 levels have reached an alarming level due to industrialization and the burning of fossil fuels. In order to lower the level of atmospheric carbon, strategies to sequester ...excess carbon need to be implemented. The CO2-fixing mechanism in photosynthetic organisms enables integration of atmospheric CO2 into biomass. Additionally, through exogenous metabolic pathways in these photosynthetic organisms, fixed CO2 can be routed to produce various commodity chemicals that are currently produced from petroleum. This review will highlight studies and modifications to different components of cyanobacterial CO2-fixing systems, as well as the application of these systems toward CO2-derived chemical production. 2,3-Butanediol is given particular focus as one of the most thoroughly studied systems for conversion of CO2 to a bioproduct.
Modification and application of different components of cyanobacterial CO2-fixing systems, for CO2-derived chemical production.
•Metabolic engineering of cyanobacteria for biofuel and bulk chemical production.•Photoheterotrophic production is improving titers in light and dark conditions.•Terpenoid biosynthesis is expanding ...range of biofuels from cyanobacteria.•Biodegradable plastic feedstocks and carbohydrate production are valuable and promising atmospheric carbon sinks.
Rising levels of atmospheric CO2 are contributing to the global greenhouse effect. Large scale use of atmospheric CO2 may be a sustainable and renewable means of chemical and liquid fuel production to mitigate global climate change. Photosynthetic organisms are an ideal platform for efficient, natural CO2 conversion to a broad range of chemicals. Cyanobacteria are especially attractive for these purposes, due to their genetic malleability and relatively fast growth rate. Recent years have yielded a range of work in the metabolic engineering of cyanobacteria and have led to greater knowledge of the host metabolism. Understanding of endogenous and heterologous carbon regulation mechanisms leads to the expansion of productive capacity and chemical variety. This review discusses the recent progress in metabolic engineering of cyanobacteria for biofuel and bulk chemical production since 2014.
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