{
  "abstract": "Cyanobacteria are promising platforms for converting CO2 directly into value-added chemicals. However, redirecting fixed carbon toward a product requires understanding of how cells balance the energetic and redox supplies and demands - and how efficiently metabolic flux can be channelled into product formation rather than being dissipated or excreted. Glycogen, synthesized via ADP-glucose pyrophosphorylase (GlgC), is the major native carbon and energy sink, and its removal forces cells to redirect excess carbon and reducing power into alternative pathways. As a target product we used ethylene, a major industrial building block currently derived almost entirely from fossil feedstocks, which can be produced photoautotrophically by the ethylene-forming enzyme (EFE) at the expense of 2-oxoglutarate (2-OG), a central node linking carbon and nitrogen metabolism. Here, we compared wild-type Synechocystis sp. PCC 6803 with strains carrying either a complete ({Delta}glgC) or attenuated, light-responsive (LGS; psbA2-driven glgC) glycogen synthesis block, with an EFE-expressing strain (EFE), and with the combined {Delta}glgC+EFE strain. All strains were cultivated across a light gradient (35-300 mol photons m-2 s-1) under nitrogen-replete conditions. Integrating measurements of growth and ethylene production rates, chlorophyll-fluorescence analysis, quantitative proteomics, FTIR profiling, and overflow-metabolite analysis revealed that partial suppression of glycogen synthesis (LGS) enhanced growth under low irradiance but became detrimental above a critical light threshold. EFE expression in the {Delta}glgC background increased ethylene production in a light-dependent manner but further compromised growth. Both strains with EFE increased photosynthetic electron transport consistent with the carbon-sink effect, yet this electron surplus was not channelled proportionally into product or biomass. Instead, continuous 2-OG drain by EFE constrained flux through the GS-GOGAT node and induced a secondary inorganic phosphate limitation in {Delta}glgC+EFE that activated photoprotection and limited productivity. These results point to the 2-OG/GS-GOGAT/Pi axis as a key design constraint determining whether the surplus photosynthetic flux gets converted into product, dissipated through photoprotection, or released as overflow metabolites.",
  "abstract_shown": true,
  "affiliations": [
    "Department of Adaptive Biotechnologies, Global Change Research Institute, Czech Academy of Sciences, Brno, Czechia"
  ],
  "article_type": "New results",
  "arxiv": null,
  "author_total": 13,
  "authors": [
    {
      "affs": [
        0
      ],
      "name": "T. Zavrel"
    },
    {
      "name": "J. Sebesta"
    },
    {
      "name": "H. Lee"
    },
    {
      "name": "T. Zlamal"
    },
    {
      "name": "T. Danisova"
    },
    {
      "name": "R. Sandor"
    },
    {
      "name": "M. Cerny"
    },
    {
      "name": "M. Berka"
    },
    {
      "name": "M. Lukes"
    },
    {
      "name": "R. Hoeper"
    },
    {
      "name": "R. Steuer"
    },
    {
      "name": "J. Cerveny"
    },
    {
      "name": "J. Yu"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/8eavmtrr6hky3.bib",
  "cited_by": 0,
  "doi": "10.64898/2026.10.25.761650",
  "fulltext_url": "https://www.biorxiv.org/content/10.64898/2026.10.25.761650v1.full",
  "id": "8eavmtrr6hky3",
  "issns": [],
  "landing_url": "https://www.biorxiv.org/content/10.64898/2026.10.25.761650v1",
  "language": null,
  "licence": "CC-BY",
  "licence_label": "CC BY",
  "licence_source": "article",
  "licence_url": "https://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": null,
  "native_subjects": [
    [
      "biorxiv",
      "plant biology"
    ],
    [
      "openalex",
      "1312|Microbial Metabolic Engineering and Bioproduction"
    ]
  ],
  "openalex": "W7223804790",
  "pdf_url": "https://www.biorxiv.org/content/10.64898/2026.10.25.761650v1.full.pdf",
  "pmcid": null,
  "pmid": null,
  "published": "2026-10-25",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/8eavmtrr6hky3.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:29:53Z",
      "native_id": "10.64898/2026.10.25.761650",
      "source": "biorxiv",
      "url": "https://www.biorxiv.org/content/10.64898/2026.10.25.761650v1"
    }
  ],
  "subjects": [
    {
      "field": "biology",
      "origin": "biorxiv:plant biology",
      "subfield": "plant-biology"
    }
  ],
  "title": "Glycogen removal enhances ethylene production in Synechocystis sp. PCC 6803 but exposes a 2-oxoglutarate-GS-GOGAT-phosphate constraint",
  "title_text": "Glycogen removal enhances ethylene production in Synechocystis sp. PCC 6803 but exposes a 2-oxoglutarate-GS-GOGAT-phosphate constraint",
  "type": "preprint",
  "updated_at": "2026-10-30T12:29:53Z",
  "url": "https://research.draconitic.com/paper/8eavmtrr6hky3",
  "venue": "bioRxiv",
  "versions": []
}