bioRxiv2025
Plasmid partitioning and bacterial conjugation are critical processes ensuring plasmid maintenance and dissemination, respectively, within bacterial populations. Although traditionally regarded as distinct phenomena, these two processes are increasingly recognized as interconnected. While partitioning ensures plasmid inheritance during cell division, its potential influence on conjugative transfer remains poorly understood. A major impediment to understanding their interplay is that partition systems are often essential for plasmid stability, making it difficult to distinguish their direct effects on conjugation. In this study, we addressed this challenge using a mini-conjugative plasmid derived from the Pseudomonas putida NAH7 plasmid. This engineered plasmid, containing all conjugation-related genes, was cloned into an E. coli-compatible vector. Additionally, the par genes from NAH7 were expressed from a separate plasmid to investigate their roles in conjugative transfer. Our results revealed that the par gene cluster plays a significant role in enhancing the conjugative transfer of the mini-conjugative plasmid. Specifically, ParB, a centromere-binding protein, functions as a transcriptional activator of conjugation-related genes with binding parSNAH site. In contrast, ParR, a KorA homolog, was not found to enhance transcription directly but binds extensively to the oriT region. This binding probably facilitates the recruitment or stabilization of the relaxosome, thereby enhancing conjugation efficiency. Together, these findings unveil a previously unappreciated role for partition proteins in stimulating bacterial conjugation, providing new insights into how plasmids coordinate vertical and horizontal dissemination, highlighting that these processes can occur simultaneously within bacterial communities. IMPORTANCEPlasmid partition systems are classified into three types. While some systems have been reported to influence conjugative transfer, this study uncovers a novel mechanism utilized by a Type I system to enhance DNA transfer. Strikingly, repeat sequences perfectly matching the parSNAH site--bound by ParB to activate downstream conjugative transfer genes--were identified on both plasmids and chromosomes across diverse proteobacterial taxa. Furthermore, many of these repeat sequences were localized near genes involved in conjugative transfer and partitioning, suggesting the presence of a conserved regulatory mechanism mediated by these repeats. This study provides important insights into how plasmid partition systems coordinate both vertical and horizontal dissemination. Such knowledge is essential for understanding and mitigating the spread of antibiotic resistance and other plasmid-encoded traits, and it offers a foundation for developing strategies to manage plasmid-associated genetic exchange.