Evolutionary and ecological feedbacks across tripartite interactions in the rhizobial community

Many organisms engage in symbioses; intimate partnerships with another species that can be mutually beneficial to both partners. However, these relationships do not occur in isolation, but are embedded within a network of interacting species, which can shape the evolution of symbiotic partnerships. The relationship between nitrogen-fixing bacteria (rhizobia) and legumes (e.g. peas and beans) is arguably one of the most economically important examples of symbiosis. Rhizobia take nitrogen from the air and convert it into a form that plants can use. This is exchanged with the plant in return for nutrients and shelter in specialized organs called root nodules. By providing the plant with a supply of nitrogen these bacteria effectively act as 'biofertilisers', reducing the need for expensive and environmentally damaging applications of chemical fertiliser to legumes as well as the non-legume crops grown alongside them.

Rhizobia do not only interact with their plant hosts however. When not living in the plant's root nodules, rhizobia live freely in the soil, interacting with the diverse microbial community that exists there. Key members of all soil microbe communities are the temperate phages, viruses that infect bacteria. These viruses can have widespread and various effects on their bacterial hosts. On the one hand they can be antagonistic, killing their host in order to produce more viral particles that will go on to infect new cells. Surprisingly however these viruses can also be beneficial. Every so often, upon infecting a bacterial cell, rather than reproducing to make more viral particles, they will integrate their own DNA into the bacterial genome, giving the bacteria access to novel genes and effectively becoming viral weapons that bacteria can use against their competitors. Rhizobia therefore engage in two important and highly contrasting interactions, with their legume hosts and with temperate phages. These separate interactions will place different selection pressures on the bacterial population and consequently are likely to have important implications for one another. This project will unpick this temperate phage - rhizobia - legume relationship in order to understand how this tripartite community shapes, and is shaped by, its constituent interactions.

This project will combine studies using highly controlled lab experiments with studies of natural and semi-natural communities. Lab experiments allow hypotheses to be directly tested and, due to the high turnover of generations in bacteria, bacteria-phage coevolution to be observed in real time. Meanwhile, experiments conducted in the 'wild' or by bringing natural communities into the lab demonstrate how real communities are structured and behave. In combination these approaches offer a powerful way of exploring these complex interactions.

This work will provide the first comprehensive examination of the role of temperate phages in rhizobial populations. With the rise in global food demand, understanding what shapes the ecology and evolution of symbiotic microbes such as rhizobia will be increasingly important. This work will therefore lay the foundation for exploring what roles the wider microbial community plays in these processes. This will lead to future work examining how we can apply these lessons to sustainable agricultural practices. For example, by using temperate phages to enhance the effectiveness of biofertilisers.

Impact on the general public:
I have a strong track record of engaging in outreach activities both within schools and with the public and intend to build on this to communicate future work. I will collaborate with the Widening Participation (WP) team at the university to develop and implement lesson plans for school-aged students. The WP team run well established, award winning initiatives aimed at inspiring children from backgrounds under-represented in academia, including those from low income areas and ethnic minorities, to engage with STEM subjects. Programs such as Green Apples and Realising Opportunities work with schools from around the country to offer pupils the opportunity to visit the university and learn about the research being conducted. I also have established links with colleges in underprivileged areas of London (Bsix, Hackney and the Robert Clack School, Dagenham) where I organise and run events for A-level students on evolutionary themes to encourage participation in STEM subjects at degree level. I will develop activity sessions on the theme of symbiosis, using games and conversation to challenge pupils to think critically about why species choose to interact and why sometimes this breaks down.

York hosts numerous forums for public engagement that are run annually, including the York Festival of Ideas and Pint of Science, which this year I ran a successful publicity campaign for. These events provide a framework in which outreach activities can be developed and delivered to a wide audience, as they have an established reputation for excellent and innovative science out reach. I will develop an interactive event to explore the diversity and importance of symbiotic interactions, from cooperation to conflict, in nature.

Impact on the agricultural community:
Though the aims of this project are predominantly 'blue skies' it will lay the ground work for future work addressing the role of within-soil interactions on the rhizobia-legume symbiosis. York-based organizations, including the N8 AgriFood Resiliance Programme, White Rose Consortium, FERA and YESI provide an interface between academia and industry. In particular schemes such as the N8 employ dedicated Knowledge Exchange teams who aim to facilitate collaboration between researchers, stakeholders and industry. I have also established links with companies, such as Legume Technology Ltd a UK based bio-inoculant company.

Through these links I will pursue partners for collaborations to translate the proof-of-concept findings from this project into field and applied studies addressing how temperate phages can impact agricultural production and sustainability. Potential projects include:
- Investigating the impact of agricultural management strategies (i.e. population mixing through tillage vs no-till farming) and phages on rhizobial population structure.

- The application of temperate phages to increase competitiveness of rhizobial seed innocula, by increasing bacterial competiveness in the soil (through increased phage resistance and acting as antimicrobial agents) and increase symbiotic function in the host (through HGT of symbiosis functions).

To establish these collaborative projects I will seek funding from sources such as the N8 pump priming scheme and BES small grant scheme as well as upcoming special interest calls, for instance through Innovate UK funding schemes. In addition the N8 program also offers opportunities to engage with the end users of research through both workshops and engagement events.