Non-Random Distribution of G-Quadruplex Structures Reveals Regulatory and Ecological Adaptations in Bacterial Genomes.

G-quadruplexes (G4s) are guanine-rich DNA secondary structures with known regulatory roles in eukaryotes, but their functions in bacteria remain largely unexplored. Here, we systematically analyzed potential G-quadruplexes (PG4s) across 1566 bacterial genomes. PG4s showed non-random distributions, with strong enrichment in intergenic regions, particularly near gene start sites, suggesting potential roles in transcriptional regulation. Structural analysis revealed a higher proportion of short-loop G4s in these regions, indicating enhanced stability. Comparisons with randomized genomes confirmed that the observed patterns cannot be explained by GC content or genome size alone. Ecological analysis further revealed that bacteria associated with homothermic hosts exhibit significantly lower G4 densities than free-living species, suggesting reduced reliance on G4-mediated regulation in stable environments. Together, these findings highlight G4s as conserved yet context-dependent elements of bacterial genome organization and provide new insights into their potential regulatory roles in prokaryotes.