Why are rhizobial symbiosis genes mobile?

Rhizobia are nitrogen fixing symbionts of legumes. They are defined by their ability to establish intracellular infections within plant hosts where they fix atmospheric nitrogen, thus allowing legumes to grow without external nitrogen inputs. Surprisingly however, key bacterial genes required for this complex trait are 'mobile' i.e. encoded on plasmids or integrative and conjugative elements - DNA elements capable of infecting new bacterial hosts. Evidence suggests that many of these elements are actively mobilizing within rhizobial populations, suggesting that regular symbiosis gene transfer is part of the ecology of rhizobial symbionts. The reasons for this, and the impact it has on rhizobial evolution are unclear. Many key questions remain outstanding, e.g. 'can symbiosis MGE transfer make anyone a symbiont?', 'what are the evolutionary consequences for bacterial genomes after acquiring this trait?', 'what environments select for symbiosis gene mobility?'

In this project we will use a combination of experimental evolution of rhizobia in the lab and in plant mesocosms alongside omics technologies such as genomics and transcriptomics and analysis of pre-existing datasets. You will learn techniques such as sterile microbiological culturing, molecular skills, bioinformatics and statistics. The project is flexible and can be guided by the interests of the student.

Please apply for this project using this link: https://www.sheffield.ac.uk/postgraduate/phd/apply/applying

Funding Notes

Self or externally funded students only.

References

https://royalsocietypublishing.org/doi/10.1098/rstb.2020.0471