My research combines a variety of techniques, from laboratory and field experiments, to bioinformatics and mathematical modelling, in order to understand how microbial populations and communities respond and adapt to changing environments. Much of my work has also used these data as a basis for predictions of how ecosystem functioning and carbon storage may vary due to global climate change. In particular my research has been focused on the effects of environmental stressors on the functioning and dynamics of microbial populations, however recently I have also investigated the effects of climate on COVID-19 transmission rates. Some highlights from past and ongoing projects are shown below.

Main Research Areas

Evolutionary dynamics of bacterial communities in the wild

Most studies of bacterial evolutionary dynamics are constrained to monoculture lab experiments. However, in the wild these organisms live in complex assemblages of interacting species. Therefore when investigating evolutionary responses of bacteria to abiotic changes, we must also consider the biotic context of the communities within which they are embedded.

Here, we are perturbing the environment of tree-holes (natural pools of rainwater that form in Beech trees) in Wytham Woods and at Silwood Park. We are using metagenomic approaches to investigate the relative importance of genetic adaptation, dispersal, and sorting of latent diversity in the responses of tree-hole bacterial communities to environmental change.

This work is with Prof. Tom Bell (Imperial) and Prof. Tim Barraclough (Oxford).

Effects of Multiple Chemical Stressors on Microbial Populations

Freshwater ecosystems are under an increasing array of threats, especially from a wide range of new and emerging chemical stressors. These ecosystems are underpinned by microbes, which perform key ecosystem functions and services. Therefore, understanding the impacts of chemical stressors on freshwater microbes is key to understanding their impacts at the ecosystem level. We are testing the impacts of chemical stressors in freshwater mesocosms, however this is labour intensive and limited in the number of chemical combinations that can be tested.

By contrast, the limits of chemical testing in the lab can be orders of magnitude higher than in the field. Here in the lab, we are testing the effects of a large array of replicated mixtures of chemicals on microbes and microbial communities, to provide a vast database of first responses to chemicals and to answer fundamental questions about interactions among chemical stressors.

This work is with Prof. Tom Bell and part of the NERC funded Emerging Risks of Chemicals in the Environment (ERCITE) project.

Relevant papers:

• "High-throughput chatacterization of bacterial responses to complex mixtures of chemical pollutants" (2024), Smith et. al. | link | research briefing

Microbial Thermal Ecology and Evolution

Bacteria and archaea (collectively "prokaryotes") are globally ubiquitous and may comprise in the region of half of the Earth's total biomass. Understanding how these diverse micro-organisms are affected by temperature is therefore key to our understanding of the impacts of climate change on ecosystem functioning.

My work on this broad topic can be roughly divided into two main aspects. Firstly, investigating how the evolution and adaptation of microbial metabolic rates is constrained by temperature, within the framework of Ecological Metabolic Theory. Secondly, understanding how changes in temperature may affect the composition of microbial communities and the impacts that these changes may have on ecosystem functioning.

This work is with Dr. Samraat Pawar and Prof. Tom Bell.

Relevant papers:

• "Community-level respiration of prokaryotic microbes may rise with global warming" (2019), Smith et. al. | link | press release
• "Adaptive evolution explains the present-day distribution of the thermal sensitivity of population growth rate" (2020), Kontopoulos et. al. | link
• "Systematic variation in the temperature dependence of bacterial carbon use efficiency" (2021), Smith et. al. | link
• "Latent functional diversity may accelerate microbial community responses to temperature fluctuations" (2022), Smith et. al. | link | press release 1 | press release 2

Other Projects (click for details)