Glycogen removal enhances ethylene production in Synechocystis sp. PCC 6803 but exposes a 2-oxoglutarate-GS-GOGAT-phosphate constraint

Removing glycogen synthesis in Synechocystis sp. PCC 6803 increases ethylene production via EFE, but in the ΔglgC+EFE strain it triggers a 2-oxoglutarate–GS–GOGAT–phosphate constraint.

• Why it matters: Redirecting fixed carbon to ethylene requires balancing energetic and redox supply with metabolic demands, yet glycogen removal can shift flux into pathways that may limit product formation.
• What they did: The study compared wild-type, ΔglgC, light-responsive LGS (psbA2-driven glgC), EFE-only, and ΔglgC+EFE strains across 35–300 mol photons m-2 s-1 under nitrogen-replete conditions, using growth/ethylene rates, chlorophyll fluorescence, quantitative proteomics, FTIR, and overflow metabolites.
• The result: LGS enhanced growth at low irradiance but became detrimental above a critical light threshold, while EFE in ΔglgC increased ethylene in a light-dependent manner yet further compromised growth; EFE’s continuous 2-OG drain constrained GS-GOGAT flux and induced inorganic phosphate limitation in ΔglgC+EFE, activating photoprotection and limiting productivity.