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Dr Tom Williams

Dr Tom Williams

Dr Tom Williams
PhD(Dub.), BA(Dub.)

Senior Research Fellow/Proleptic Senior Lecturer

Area of research

Phylogenetics, molecular and microbial evolution

Life Sciences Building,
24 Tyndall Avenue, Bristol BS8 1TQ
(See a map)


I'm a computational evolutionary biologist. Work in my group uses computational methods (mostly phylogenetics and bioinformatics) to study how molecules, genomes and microbes evolve, and to learn about the evolutionary history of life.

Current group members include

  • Dr. Celine Petitjean (NERC PDRA): eukaryote phylogeny and genome evolution
  • Dr. Paul O. Sheridan (NERC PDRA, with Cecile Gubry-Rangin, Aberdeen): genome evolution of Thaumarchaeota
  • Dr. Christopher Kay (BBSRC PDRA, with Wendy Gibson, Bristol): trypanosome genomics
  • Gareth Coleman (Royal Society PhD student): bacterial evolution
  • Edd Moody (Royal Society PhD student): evolution of protein folds
  • Brogan Harris (PhD student, with Alistair Hetherington, Bristol): gene family evolution in land plants
  • James Fearn (PhD student, with Colin Campbell, Bristol): machine learning approaches to biological data analysis
  • Matt Tarnowski (PhD student, with Tom Gorochowski, Bristol): using evolutionary information in synthetic biology
  • Dan Macrae (PhD student, with Patricia Sanchez-Baracaldo, Bristol): evolution of symbiotic cyanobacteria
  • Hend Abu Elmakarem Abdelrahman (MSc Res student): genomics of free-living eukaryotic microbes
  • Kate Cook (MSc Res student): evolution of trypanosome genome structure

 Get in touch if you are interested in joining; I also take interested Masters students from Biological Sciences and Earth Sciences.


Early cellular evolution

I'm fascinated by the earliest stages of cell evolution, including the origins of bacteria, archaea, eukaryotes, and the relationships between them. I am applying phylogenetic and comparative genomic approaches to reconstruct the common ancestors of these groups and to draw inferences about the conditions in which they evolved on the early Earth. Working back from modern genomes to understand ancient events challenges current methods to their limits, and so I work with statisticians to develop and apply new approaches that bring new kinds of data to bear on these challenging problems. These methods include non-stationary and non-reversible substitution models, which enable the root of a phylogenetic tree to be inferred as an integral part of the analysis. They also include probabilistic supertree and gene tree-species tree reconciliation approaches, which promise to harness genome-wide evolutionary patterns to resolve the most ancient parts of the tree of life.

The origin of eukaryotes

I maintain a long-term interest in the origin of eukaryotic cells --- the compartmentalized cells containing a mitochondrion and nucleus that form the basis for the complex life we see around us every day, from a diversity of single-celled forms through plants, fungi, and animals, including humans. The balance of evidence now places a symbiosis between an archaeal host cell and a bacterial endosymbiont --- members of the two major prokaryotic domains --- as a foundational event in the origin of eukaryotes. Much of my work in recent years has focused on testing hypotheses for eukaryote origins, and ongoing work at Bristol involves identifying our closest archaeal relatives and working out how the complex cellular features of modern eukaryotes evolved from their prokaryotic progenitors.

Eukaryotic genome diversity and evolution

While to many of us, the most familiar eukaryotes are the four main multi cellular lineages --- plants, animals, fungi and brown algae --- the great majority of eukaryotic genetic diversity is found among single-celled forms, and several of the most biodiverse eukaryotic groups are entirely unicellular. Current work focuses on comparative genomics of two groups in particular: (i) the microsporidians, obligate intracellular parasites related to fungi, which are fascinating model systems for studying the limits of eukaryotic genome reduction; and (ii) the excavates, a very diverse and poorly-understood group of microbial eukaryotes that contains both serious parasites (trypanosomes, Giardia, Trichomonas), as well as abundant and ecologically important free-living forms.


I obtained a B.A. in Genetics (2007) and a Ph.D. in molecular evolution (2010) from Trinity College Dublin. My Ph.D. work with Mario Fares focused on the evolution of molecular chaperones in Bacteria and Archaea, and on the effect of chaperone-mediated buffering of destabilising mutations on protein evolutionary rates. From 2010-2015, I was a Marie Curie Fellow and then a Research Associate in Martin Embley's group at Newcastle University, working on phylogenomics and eukaryotic genome evolution. In 2015, I came to Bristol as a Royal Society University Research Fellow, first in Earth Sciences and now in the School of Biological Sciences. I am a member of the Palaeobiology and Biodiversity Research Group.



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