PlasAnn: a curated plasmid-specific database and annotation pipeline for standardized gene and function analysis.

Conjugative plasmids are key drivers of bacterial adaptation, enabling the horizontal transfer of accessory genes within and across diverse microbial populations, yet annotating them remains challenging due to their highly mosaic genetic architectures and inconsistent gene naming conventions that complicate functional predictions and comparative analyses. To address this, we developed PlasAnn, a database designed specifically for genes encoded on natural plasmids, paired with a dedicated annotation pipeline (available via Bioconda or through the URL https://plasann.rochester.edu/). The curated database provides highly accurate, plasmid-type-specific gene names with standardized functional annotations, enabling direct comparison across plasmids without manual curation or specialized expertise, while the integrated annotation tool incorporates other common plasmid features for a fast, one-stop solution that outperforms broad prokaryotic genome annotation pipelines in both accuracy and efficiency. We demonstrate PlasAnn's utility by showing that plasmid accessory genes from different groups often share conserved repertoires, suggesting dynamic, modular networks of interconnected genes, and by revealing that plasmid-encoded transposable elements frequently carry genes related to bacterial adaptation beyond antibiotic resistance, including metabolism, virulence, and stress responses, emphasizing their broader contributions to fitness and adaptability. These insights, not captured by current field-standard tools, highlight how PlasAnn improves plasmid annotation and advances our understanding of plasmid biology, microbial ecology, and evolution.