biostudies-literatureUnknown16(2)Simonsen AKBacteria have highly flexible pangenomes, which are thought to facilitate evolutionary responses to environmental change, but the impacts of environmental stress on pangenome evolution remain unclear. Using a landscape pangenomics approach, I demonstrate that environmental stress leads to consistent, continuous reduction in genome content along four environmental stress gradients (acidity, aridity, heat, salinity) in naturally occurring populations of Bradyrhizobium diazoefficiens (widespread soil-dwelling plant mutualists). Using gene-level network and duplication functional traits to predict accessory gene distributions across environments, genes predicted to be superfluous are more likely lost in high stress, while genes with multi-functional roles are more likely retained. Genes with hThe ISME journal423-434https://www.ebi.ac.uk/biostudies/studies/S-EPMC8776746biostudies-literatureEnvironmental stress leads to genome streamlining in a widely distributed species of soil bacteria.PMC8776746Simonsen AKfalseEnvironmental stress leads to genome streamlining in a widely distributed species of soil bacteria.Bacteria have highly flexible pangenomes, which are thought to facilitate evolutionary responses to environmental change, but the impacts of environmental stress on pangenome evolution remain unclear. Using a landscape pangenomics approach, I demonstrate that environmental stress leads to consistent, continuous reduction in genome content along four environmental stress gradients (acidity, aridity, heat, salinity) in naturally occurring populations of Bradyrhizobium diazoefficiens (widespread soil-dwelling plant mutualists). Using gene-level network and duplication functional traits to predict accessory gene distributions across environments, genes predicted to be superfluous are more likely lost in high stress, while genes with multi-functional roles are more likely retained. Genes with h2022-01-01T00:00:00Z2022 Feb2026-05-09T03:01:07.037Z2025-04-06T14:57:34.453ZS-EPMC87767463440826810.1038/s41396-021-01082-x