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Metabolome Profiling of a Fast-growing Cyanobacterium Synechococcus elongatus PCC 11801 under Diurnal Cycle

ABSTRACT: Experiments were carried out by growing Synechococcus elongatus PCC 11801 cells in multicultivators designed to provide sinusoidal light. The period was 14:10 (light-dark). The samples for metabolomics analysis were collected in the second diurnal cycle at an interval of 6 hours starting from 25th hour (25, 31, 37 and 43 hours). The light intensity amplitude was 600 µmole photons.m-2. s-1. Additionally samples were also collected using cells grown under continuous light illumination of 600 µmole photons.m-2. s-1 to compare the difference in metabolite levels compared to that in the diurnal cycle.

ORGANISM(S): Synechococcus Synechococcus Elongatus Pcc 11801

TISSUE(S): Bacterial Cells

SUBMITTER: Pramod P Wangikar

PROVIDER: ST001302 | MetabolomicsWorkbench | Mon Jan 06 00:00:00 GMT 2020

REPOSITORIES: MetabolomicsWorkbench

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Project description:Biological CO2 mitigation by photosynthetic microorganisms has emerged as a promising approach for generating biomass-based energy during the course of CO2 fixation. Additionally, cyanobacteria-based biofuels have also garnered immense attention lately because of the depleting fossil fuel reserves and the growing energy demands. Synechococcus elongatus PCC 11801, a fast-growing, high CO2 tolerant, novel isolate of cyanobacteria, is an interesting candidate for metabolic engineering applications. Since under laboratory conditions, it exhibited a high level of tolerance to different environmental stresses (CO2, light, temperature, salts and butanol), it seemed like an encouraging prospect for the production of fuels and other industrially relevant chemicals. This is the first-ever functional global proteomics investigation of Synechococcus elongatus PCC 11801 isolate grown at elevated CO2 levels using high-throughput iTRAQ approach. Three independent biological replicates were analyzed and a total of 861 proteins were identified, out of which 492 proteins were found to be present in all the three replicates. Of these, 248 proteins showing the same trend across the three replicates (≥1.5 fold up-regulation or ≤0.66 fold down-regulation) were chosen for pathway analysis. The metabolic responses were marked with a down-regulation of inorganic carbon transporters alongside an induction of nitrogen transport and absorption proteins in order to uphold the apposite carbon-nitrogen equilibrium. Further acclimation progression exposed an increased expression of proteins taking part in photosynthesis and generation of light harvesting pigments such as chlorophyll. Similarly, a downshift of proteins involved in photoprotection and defense against ROS (reactive oxygen species) was observed. Another principal discovery was the perturbation in expression of proteins belonging to central metabolic pathways like glycolysis, TCA cycle, pentose phosphate pathway as a coping mechanism to high CO2 stress. Further, validation studies were carried out using MRM assays and western blotting of key altered proteins.

Project description:Background:Cyanobacteria, a group of photosynthetic prokaryotes, are being increasingly explored for direct conversion of carbon dioxide to useful chemicals. However, efforts to engineer these photoautotrophs have resulted in low product titers. This may be ascribed to the bottlenecks in metabolic pathways, which need to be identified for rational engineering. We engineered the recently reported, fast-growing and robust cyanobacterium, Synechococcus elongatus PCC 11801 to produce succinate, an important platform chemical. Previously, engineering of the model cyanobacterium S. elongatus PCC 7942 has resulted in succinate titer of 0.43 g l-1 in 8 days. Results:Building on the previous report, expression of ?-ketoglutarate decarboxylase, succinate semialdehyde dehydrogenase and phosphoenolpyruvate carboxylase yielded a succinate titer of 0.6 g l-1 in 5 days suggesting that PCC 11801 is better suited as host for production. Profiling of the engineered strains for 57 intermediate metabolites, a number of enzymes and qualitative analysis of key transcripts revealed potential flux control points. Based on this, we evaluated the effects of overexpression of sedoheptulose-1,7-bisphosphatase, citrate synthase and succinate transporters and knockout of succinate dehydrogenase and glycogen synthase A. The final construct with seven genes overexpressed and two genes knocked out resulted in photoautotrophic production of 0.93 g l-1 succinate in 5 days. Conclusion:While the fast-growing strain PCC 11801 yielded a much higher titer than the model strain, the efficient photoautotrophy of this novel isolate needs to be harnessed further for the production of desired chemicals. Engineered strains of S. elongatus PCC 11801 showed dramatic alterations in the levels of several metabolites suggesting far reaching effects of pathway engineering. Attempts to overexpress enzymes deemed to be flux controlling led to the emergence of other potential rate-limiting steps. Thus, this process of debottlenecking of the pathway needs to be repeated several times to obtain a significantly superior succinate titer.

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Metabolome Profiling of a Fast-growing Cyanobacterium Synechococcus elongatus PCC 11801 under Diurnal Cycle

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