Global metabolic rewiring for improved CO2 fixation and chemical production in cyanobacteria

Abstract

Cyanobacteria have attracted much attention as hosts to recycle CO2 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 CO2 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 CO2 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.

A comprehensive time‐course metabolite profiling of the model cyanobacterium Synechocystis sp. PCC 6803 under diurnal light:dark cycles

“…Previous reports of cyanobacteria growth in sinLD cycles are limited as much of the work has been performed in a chemostat‐like environment (Beck et al ., ; Diamond et al ., ; Angermayr et al ., ), or were not reported with enough temporal sensitivity to discern the timing of cell division (Hanai et al ., ; Cheah et al ., ; Saha et al ., ). Still, several studies report increased OD during the day in diurnal LD cycles (Angermayr et al ., ; Hanai et al ., ; Kanno et al ., ; Werner et al ., ), and circadian studies of S. elongatus PCC7942 report cell division during the circadian day (Mori et al ., ). These reports agree with our observations.…”

Synthetic Biology Toolkits for Metabolic Engineering of Cyanobacteria

“…However, it is difficult to concurrently employ multiple genetic sites for strain engineering with current integration approaches, thus chromosomal integration for expression of heterologous genes to assemble synthetic pathways is hampered. One reason is the limited choice of antibiotic markers, which is necessary for selecting transformants, and the other is the inhibition of cellular metabolism upon accumulation of markers from integrated cassettes, which is deleterious to cell viability as antibiotics are typically required during cultivation to ensure maintenance of the integrated genes . Therefore, methods for curing the markers or markerless integration techniques are necessary to enable efficient chromosomal expression and will be discussed in the following section.…”

“…Such methods have been employed for metabolic engineering to understand and improve biosynthetic pathways. For instance, Kanno et al constructed six single‐gene deletion strains with the replacement of essential genes in relevant pathways and discovered the key genes for 2,3‐butanediol production, leading to an engineered strain with supreme productivity. However, to facilitate multiloci editing, the markers need to be removed to prevent accumulation of antibiotic‐resistant genes and enable recycling of the markers.…”

Modular engineering for efficient photosynthetic biosynthesis of 1-butanol from CO2in cyanobacteria

“…1,2 On the other hand, CO 2 can be directly recycled into biofuels using solar energy by engineered photosynthetic microorganisms, such as cyanobacteria. [3][4][5][6][7][8][9][10][11] These so called solar fuels and chemicals represent potentially cheaper and more sustainable alternatives to traditional biofuels, with the capacity to replace fossil fuels. A prerequisite for pursuing this option is to develop cyanobacteria as efficient green microbial cell factories for directly producing biofuels and biochemicals.…”