Flagellar rotation facilitates the transfer of a bacterial conjugative plasmid

Conjugation-mediated DNA delivery is the primary mode for antibiotic resistance spread in bacteria; yet, molecular mechanisms regulating the conjugation process remain largely unexplored. While conjugative plasmids typically require bacterial attachment to solid surfaces for facilitation of donor-to-recipient proximity, the pLS20 conjugative plasmid, prevalent among Gram-positive Bacillus spp., uniquely requires fluid environments to enhance its transfer. Here we show that pLS20, carried by B. subtilis, induces multicellular clustering, which can accommodate various species, hence offering a stable platform for DNA delivery in liquid milieu. We further discovered that induction of pLS20 promoters, governing crucial conjugative genes, depended on the presence of donor cell flagella, the major bacterial motility organelle. Moreover, the pLS20 regulatory circuit is regulated by a mechanosensing signal transduction pathway responsive to flagella rotation, thus activating conjugation gene expression exclusively during the host motile phase. This flagella-conjugation coupling strategy may allow dissemination of the plasmid to remote destinations, allowing infiltration into new niches.