Polyphosphate acts as an architectural regulator of carbon fixation and nucleoid structure in cyanobacteria.

Polyphosphate granules in Synechococcus elongatus localize to the nucleoid and are periodically arranged along the cell axis, independently of the McdAB carboxysome positioning system.

• Why it matters: The work addresses how constitutively present polyP is organized in cyanobacteria and how it shapes photosynthetic cytoplasm architecture to support CO2 fixation.
• What they did: The authors mapped polyP and carboxysomes, tested dependence on McdAB positioning, and analyzed phenotypes after loss of polyP synthesis or perturbing polyP turnover.
• The result: Removing polyP synthesis expands the nucleoid, increases smaller high-mobility carboxysomes, and causes severe growth defects under ambient CO2, with turnover perturbations linking polyP to carboxysomes and thylakoid membranes.

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