The dynamics of rhizoplane colonisation: quantification of the early stages of lettuce root colonisation by Pseudomonas fluorescens SBW25

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The Microbiology Society is undertaking a project entitled A Sustainable Future as part of our 75th Anniversary, which aims to highlight the Sustainable Development Goals (SDGs) to our members and empower them to use their research to evidence and impact the goals. Earlier this year, we put a call out to our members to submit case studies in the following three areas: antimicrobial resistance, soil health and the circular economy.

This case study is written by Daire Carroll, who is a PhD researcher at the University of Warwick and the James Hutton Institute, and a member of the Microbiology Society. It focuses on Soil Health; maintaining the health of our soils has gained increasing prominence in recent years. Soils are essential for the global food system and regulate water, carbon and nitrogen cycles but are put under pressure from population growth and climate change.

This PhD project is jointly funded by the University of Warwick and the James Hutton Institute. The project is being carried out by Daire Carroll, supervised by Dr Lionel Dupuy and Dr Nicola Holden at the James Hutton Institute, and Dr Miriam Gifford at the University of Warwick. It makes use of the expertise and resources of both institutes, working across microbiology, soil biophysics, and plant science laboratories. Its aim is to develop a framework for the quantification and modelling of plant root surface colonisation by bacteria.  

What are the challenges the research addresses?

In modern agriculture, growers face the increased risk of extreme weather events, as well as emerging pathogens. At the same time, environmental awareness and restrictions on chemical treatments are limiting the options available to growers for maintaining their yields. Plant growth promoting bacteria have been the focus of much research and speculation. They can be harnessed to maintain crop growth and production under stressful conditions, such as drought. Roots are the first point of interaction between plants and soil borne micro-organisms.

Currently, integration of plant growth-promoting micro-organisms into agricultural practice is low. Part of the reason for this is the difficulty of translating promising results from growth chamber and greenhouse trials to the field. The lack of a suitable tool to assess and predict the colonisation of plant roots by bacterial strains contributes towards this.

A key limitation of studies focused on root colonisation is that it is difficult to access the contributions of individual bacterial processes, such as attachment and proliferation. This project aims to address this knowledge gap and produce a model of root surface colonisation which accounts for both attachment and proliferation.

What findings were provided by this research?

This project has used a model system composed of the plant growth promoting bacterial strain, Pseudomonas fluorescens SBW25, and lettuce (Lactuca sativa L.). It has developed a framework which can determine microbial attachment and proliferation rates on the root surface based on parameters, which can easily be experimentally quantified. This has enabled the relative contributions of attachment and proliferation at any point during the colonisation process to be determined.

How can this research support the transition to a more sustainable future?

Understanding the interaction between plant roots and bacteria is a key component of research into plant growth-promoting micro-organisms. The ability to predict and understand how different components of microbial activity contribute towards colonisation will enable the assessment of potential growth-promoting micro-organisms as agricultural tools.

In the future, this could allow selection of microbial traits that improve early colonisation and maintenance of targeted strains in cropping systems. In turn, this can help with the move towards less environmentally damaging agricultural practices and a more sustainable future. 

What is the future of research and innovation in this area?

The theoretical and experimental frameworks developed during this project will be used alongside imaging to continue to improve our understanding of microbial colonisation of root surfaces. Going forward, the system will be used to quantify the process of colonisation for a broader range of microbial strains and crop species.


We would like to thank the James Hutton Institute and the University of Warwick for funding this project and the staff of both institutes for their ongoing support. 

About the Author

Daire Carroll is a PhD researcher at the University of Warwick and the James Hutton Institute. More information about his work is available here.