Factors Altering Pyruvate Excretion in a Glycogen Storage Mutant of the Cyanobacterium, Synechococcus PCC7942

Area of Science:

• Metabolic Engineering
• Synthetic Biology
• Cyanobacterial Physiology

Background:

• Cyanobacteria are key targets for metabolic engineering to produce carbon commodities from CO2.
• Nitrogen deprivation redirects carbon flux, often towards glycogen storage.
• Pyruvate is an industrially valuable compound with potential for bio-production.

Purpose of the Study:

• To engineer Synechococcus elongatus PCC 7942 for enhanced pyruvate production.
• To investigate the impact of nitrogen deprivation and genetic modification on carbon flux.
• To optimize conditions for extracellular pyruvate excretion.

Main Methods:

• Generated a knockout mutant (ΔglgC) in ADP-glucose pyrophosphorylase to block glycogen synthesis.
• Cultured the mutant under nitrogen-deprived conditions at varying pH levels.
• Engineered the mutant to express foreign transporters for photomixotrophic growth with glucose or sucrose.
• Measured extracellular pyruvate accumulation.

Main Results:

• The ΔglgC mutant excreted pyruvate under nitrogen deprivation for the first time.
• Elevated culture pH to 10 significantly increased pyruvate excretion.
• Photomixotrophic growth with glucose resulted in a fourfold increase in pyruvate excretion compared to sucrose.
• Pyruvate excretion correlated positively with starter culture density, not photosynthetic activity.

Conclusions:

• Blocking glycogen synthesis in cyanobacteria is an effective strategy for pyruvate overproduction.
• Optimizing culture pH and utilizing photomixotrophy with glucose can enhance pyruvate yields.
• Further research is needed to elucidate the carbon source for pyruvate and the export mechanism.