Current Research Themes
Plants form complex associations with a large diversity of soil microorganisms. Soil microbes are critical for plant growth, soil health and ecosystem function making them key targets for further research, both to understand the future of ecosystems and as targets of manipulation for human benefit.
Rhizobia and their Legumes HostsEco-evolutionary interplay between free-living and symbiosis stages in plant symbionts I study nitrogen-fixing symbionts that associate with legume roots (a.k.a. rhizobia). Although microscopic, rhizobia play a major role in global nitrogen-cycles because both they and their plant hosts are so globally widespread. Rhizobia spend much of their time as free-living colonies in the soil so my goal is to understand how selective pressures from the soil environment impact how these symbionts associate with their hosts. For example, do more stressful soil environments lead to a stronger mutualistic relationship, or can it lead to a mutualism break down? How does the soil environment impact the dynamics of horizontally transferred genes, including genes that control symbiosis? I will be exploring these and other questions, moving towards the broader goal of understanding how we can leverage mutualistic relationships between plants and bacteria for various applications, such as regenerative agriculture and habitat restoration in a changing climate. Mechanisms of symbiont specialisation to their plant hosts Legumes are one of the most diverse plant families in the world that grow on every continent. Legumes have co- evolved highly specialised relationships with rhizobia, but these relationships are quite complex. We currently have a poor understanding of why some legume species form associations with lots of different rhizobia species, while other legume species have very narrow requirements. We are currently investigating patterns of specialization between legumes and rhizobia from multiple biomes. |
Microbes and their Soil HabitatThe evolution of the pangenome in microbial symbionts All cells contain a genome. The last two decades of research have shown that bacteria, even within the same species complex show remarkable variation in genome content among different strains. While all strains possess a "core" genome, many strains carry unique genes that are only present in a subset of strains in natural soil population. My research in Bradyrhizobium (a commonly occurring rhizobia) genome evolution has shown that some populations can show as much as 10% difference in genome size. Key findings show that environmental stress leads to reductions in genome size, showing that the environment imposes evolutionary changes that alter structural variation in the genome. How does continental isolation affect soil microbe diversity? Antarctica has been a geographically isolated landmass for a long time. However, some microorganisms are able to disperse long distances through oceanic and atmospheric currents over short time periods. Here, I am using biogeographic models that incorporate evolutionary and ecological mechanisms to identify and infer dispersal events into Antarctica from other regions. These analyses provide informative baseline information that identifies particular lineages that have a higher evolutionary tendency to disperse into Antarctica, and an estimated time period on when those major dispersal events happened. As climate continually changes in the continent, it is more likely that the Antarctic will experience changes in its resident microbial communities, either because the continent is colonised by new microbial species or because new environmental conditions promote the evolution of new microbial assemblages. Our evolutionary analysis of existing lineages and past dispersal events should provide critical information that will help to predict the nature and extent of the changes in Antarctica, necessary for informed management of the Antarctic biosphere into the future. |