The role of plasmids in adapting bacteria of the genus Sphingomonas to life on plants.

Beneficial bacteria can improve plant health and contribute to sustainable agriculture.

The genus Sphingomonas is promising in this regard as some strains can improve plants’ abiotic tolerances, protect against pathogens, and promote growth.

They are highly abundant on a variety of plants worldwide, and may thrive on plants thanks to their plasmids; not only do plasmids frequently carry genes with functions specialized for unique environments, but many are also transmissible between cells, allowing a population of bacteria to share genes and rapidly adapt.

This project will catalog, characterize, and evaluate the usefulness of plasmids in Sphingomonas strains isolated from diverse plant-associated habitats in Sweden – in particular leaves and roots of a dicot (Arabidopsis thaliana), monocot (Hordeum vulgare, barley), and gymnosperm (Picea abies, Norway spruce).

We will characterize over 1000 Sphingomonas genomes and their associated plasmids to estimate plasmid prevalence and signatures of adaptation.

We will also measure the stability of a large panel of plasmids when challenged with treatments designed to remove them.

Finally, we will mix together strains having all, some, or none of their plasmids removed and let them compete on plants to determine the positive contribution of plasmids to bacterial fitness.

This project determines how plasmids may enable bacteria to thrive on plant hosts, and forms a foundation for future “breeding programs” for beneficial bacteria.