Don't go out there! How do bacteria-phages interactions in the soil impact the rhizobia-legume symbiosis

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Rhizobia (nitrogen-fixing bacteria) are a classic model formutualistic interactions - they form intimate intracellularsymbioses with legumes where they exchange nitrogen fornutrients and shelter. The rhizobia-legume symbiosis has beenstudied near-exclusively as a pairwise interaction, but in realityis embedded within a complex species community withconsequences for each partner and thus the symbiosis.Between plant-hosts rhizobia live as free-living bacteria within adiverse soil microbial community including phages (bacterialviruses) - the primary predators of bacteria. Phage predationcould shape the rhizobia-legume symbiosis in numerous ways;phages drive continuous selection for phage resistance(antagonistic coevolution) which may result in pleiotropic trade-offs in the symbiosis. Conversely, higher mortality outside maydrive greater symbiotic investment by increasing the value ofprotection within the plant, i.e. altering the 'economics' of theinteraction. In this project we will combine experimentalevolution, next-generation sequencing and mathematicalmodelling to ask a critical overlooked question - how dointeractions outside the host shape the rhizobia-legumesymbiosis