bims-nucleo 2026-08-23 papers

Issue of 2026–08–23
two papers selected by
Ishika Gupta

bioRxiv. 2026 Aug 04. pii: 2026.08.04.742738. [Epub ahead of print]

The roles and synthesis of inorganic polyphosphate in Bacillus cereus.

Christine Kim, Lilla Fournier, Michael J Gray, Christopher W Hamm.

Inorganic polyphosphate (polyP) is a universally conserved biopolymer central to bacterial stress survival, yet understanding of its roles derives almost entirely from Gram-negative models in which polyP accumulates intracellularly following nutrient downshift. We examined polyP metabolism in the Gram-positive spore-forming bacterium Bacillus cereus using deletions of the polyP kinases PPK1 and PPK2 and the exopolyphosphatase PPX. Intracellular polyP synthesis required PPK1 and was opposed by PPX and PPK2: ppx mutants accumulated polyP in sporulation medium by 24 hours, ppx ppk2 double mutants accumulated more, and no ppk1 mutant accumulated any. A ppk1 ppx double mutant could not be generated, suggesting that unopposed PPK2 activity is lethal. Unlike Escherichia coli and Pseudomonas aeruginosa , B. cereus did not accumulate polyP after shift to minimal medium, increasing only modestly in stationary phase. Fluorescence and transmission electron microscopy localized intracellular polyP to electron-dense granules within ribosome-depleted cytoplasm. Cells bearing these granules remained membrane-intact yet failed to resume growth over 8 hours in rich medium, leading us to propose that polyP drives ribosome sequestration into condensates and a hibernation-like state. Unexpectedly, B. cereus also released close to 100µM polyP extracellularly during late stationary phase, even in a ppk1 ppk2 mutant lacking both known synthetases. Extracellular polyP resisted hydrolysis by purified PPX even after deproteinization, indicating an atypical structure. Bacillus thuringiensis and Bacillus anthracis released similar amounts of extracellular polyP. Together these results identify two distinct polyP pools in the B. cereus group: a PPK1-dependent intracellular pool and an extracellular pool made by an uncharacterized pathway.
Importance: Bacillus cereus is a spore-forming bacterium that causes foodborne illness and persists in soil and food-processing environments, where survival depends on managing phosphate and energy reserves during starvation. Inorganic polyphosphate (polyP), an ancient polymer used by nearly all cells to withstand stress, has been studied almost entirely as a molecule stored inside bacteria. We show that Bacillus cereus maintains two separate polyP pools. The internal pool is made by a known enzyme (PPK1) and is associated with dormant cells whose protein-making machinery appears to be packed away. The external pool is made without any known polyP-synthesizing enzyme, pointing to a novel polyP synthesis pathway that is shared with the close relatives Bacillus thuringiensis and Bacillus anthracis .

DOI: https://doi.org/10.64898/2026.08.04.742738

mBio. 2026 Aug 19. e0099926

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

Claire E Dudley, Daniel J Foust, David F Savage, Julie S Biteen, Anthony G Vecchiarelli.

Polyphosphate (polyP) is a conserved inorganic polymer traditionally viewed as a stress-induced phosphate and energy reserve. In cyanobacteria, however, polyP granules are constitutively present and are frequently observed in close proximity to carboxysomes, the bacterial microcompartments that mediate CO2 fixation. Here, we show that polyP functions as a spatially organized regulator of the photosynthetic cytoplasm in Synechococcus elongatus. PolyP granules localize to the nucleoid and are periodically arranged along the cell axis, independent of the McdAB carboxysome positioning system. Despite this independence, polyP and carboxysomes associate non-randomly, and this association is enhanced when active carboxysome positioning by the McdAB system is disrupted. Loss of polyP synthesis leads to nucleoid expansion, an increased number of smaller carboxysomes with high mobility, and severe defects in growth under ambient CO2. Perturbation of polyP turnover further reveals structural connections to both carboxysomes and thylakoid membranes. Together, these findings identify polyP as an architectural integrator that couples chromosome organization, metabolic compartmentalization, and photosynthetic fitness.IMPORTANCEPolyphosphate (polyP) is a ubiquitous storage polymer found across all three domains of life. In bacteria, polyP is involved in virulence, energy metabolism, DNA structure, and stress. Here, we investigate the physical and functional relationships between polyP and the carboxysome-a carbon-fixing organelle that encapsulates the most abundant enzyme on Earth and is responsible for a significant amount of atmospheric CO2 sequestration. We discover that polyP is important for proper carboxysome assembly and organization in the cell and is also required for robust cell growth under ambient CO2 conditions. As carboxysomes are one class of the broader group of bacterial microcompartments, these findings have broader implications for polyP in the function and organization of the bacterial cytoplasm.

Keywords: bacterial microcompartments; bacterial organelles; carboxysomes; polyphosphate (polyP); subcellular organization

DOI: https://doi.org/10.1128/mbio.00999-26