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This study investigates how glycogen-deficient Synechocystis cyanobacteria cope with day-night cycles, using single-cell microfluidics, transcriptomics, and metabolomics. During the day, mutants lacking the glgC gene suppress photosynthesis-related gene expression to avoid excess NADPH accumulation in the absence of glycogen as a carbon sink. At night, these mutants suffer severe energy deficits, including depleted ATP, disrupted redox balance, and accumulation of fumarate and malate, ultimately causing delayed cell division and prolonged lag phases after dawn.
Why it matters
Understanding how cyanobacteria manage carbon storage and energy metabolism during light-dark cycles has direct relevance to engineering more productive photosynthetic organisms for biotechnological applications such as biofuel production. These findings also shed light on the evolutionary pressures that shaped metabolic dependencies in endosymbiotic relationships, including those that gave rise to plant chloroplasts.
⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Diurnal changes in light availability are a defining feature of life on Earth. Photoautotrophic organisms therefore store reduced carbon during the day to sustain energy metabolism at night. In cyanobacteria, glycogen is the primary carbon storage compound and supports both energy homeostasis and stress responses. Although glycogen-deficient Synechocystis strains have been studied previously, how these mutants cope with the loss of the major daytime carbon sink and can sustain themselves during the night remains unclear. Using single-cell microfluidics, transcriptomics, and metabolomics, we show that {Delta}glgC mutants exhibit pronounced light sensitivity. At sub-lethal light intensities, daytime transcriptional responses are dominated by downregulation of photosynthesis-related genes, likely preventing NADPH overaccumulation in the absence of a carbon sink. During the night, mutants display severe energy limitation, characterized by reduced ATP levels, altered redox balance, and depletion of central carbon intermediates. In contrast, fumarate and malate accumulate, indicating enhanced respiratory flux through succinate dehydrogenase. These metabolic constraints lead to extended lag phases and delayed cell divisions after the onset of light, demonstrating that glycogen-deficient cells fail to efficiently reinitiate growth after dawn. Overall, our results as a snapshot of the initial response to diurnal regimes highlight glycogen as a central integrator of diurnal physiology in Synechocystis, coordinating energy metabolism, redox balance, and cell division, with implications for metabolic robustness and the evolutionary constraints shaping (endo)symbiosis.
Source: Glycogen deficiency impairs diurnal energy metabolism and cell division in Synechocystis