Trade-off between vertical and horizontal gene transfer in bacteria – GeTBac

Plasmid-mediated horizontal gene transfer is largely involved in the problematic emergence of antimicrobial resistance (AMR) in bacteria, as well as the propagation of other genetic traits such as virulence or metabolic functions. This has important implications for humans, animals, the environment, and the economy, as well as the diversity and evolution of bacteria.
As carriers of mobile genetic elements, including transposons, integrons, and associated passenger genes, conjugative plasmids behave as gene shuttles able to propagate within bacterial populations. Plasmid propagation occurs both vertically by plasmid segregation to daughter cells during proliferation and horizontally to other bacteria during transfer by conjugation. These two modes of transfer require dedicated machinery. Segregation involves systems that position plasmids at appropriate subcellular locations to ensure that each daughter cell receives at least one copy of the plasmid, while conjugation requires systems that transfer plasmid copies unidirectionally between contacting bacteria using a DNA processing system coupled to a type IV membrane secretion system. Clearly, these systems involve and require mutually exclusive subcellular localization of plasmids, i.e., plasmid copies must be moved from their position, usually in the nucleoid area, to the membrane to conjugate. How they switch from one to the other is still largely elusive. This is true not only in the donor bacterium but also in the recipient bacterium that has just acquired a conjugative plasmid and becomes a new stable donor, thus contributing to the exponential spread of AMR. Yet, this checkpoint in plasmid trafficking has received very little attention until now.
The Stb system, which is found in over 15% of enterobacterial plasmids, is the only system linking plasmid subcellular localization with both segregation and conjugation efficiencies. The GeTBac project, which is based on strong and promising preliminary data, aims at describing in depth the roles of Stb proteins, their consequences on plasmid localization, and fate. This includes the use of the nematode Caenorhabditis elegans as a model, which features should allow for the first-time direct imaging of conjugative events in a gastrointestinal system model, opening the way to describing the fine controls of gene exchanges inside host-associated bacterial communities. To achieve these objectives, we will use a combination of complementary, multi-scale approaches in which the three partners of the consortium have recognized expertise, from the molecular and cellular levels to the bacterial population level. This includes genetics, biochemistry, genome-wide techniques, as well as state-of-the-art cell imaging.
The GeTBac basic research proposal is designed to provide an integrated view of plasmid DNA transmission in bacterial populations, which is central to the evolution and diversification of the bacterial genome. This will generate important knowledge on a major pathway for the spread of AMR and, in the longer term, may help identify alternative strategies to antimicrobials, which is one of the actions to be taken in response to the "One Health" strategic priority of curbing the silent AMR pandemic.