PhD in Genomics, Evolution and Computational Phylogenetics:Timing and evolution of cyanobacterial symbioses

Cyanobacteria have had a huge impact on the biological diversity of the Earth’s ecosystems, in part due to their ability to establish symbiotic relationships with several different hosts. Cyanobacterial symbioses are widely distributed in marine, freshwater and terrestrial environments and these involve taxonomically diverse hosts. Symbionts shape the biology and evolution of their hosts by providing a range of benefits such as photosynthesis, nitrogen fixation, UV protection, and defensive toxins. Symbionts are also found across the cyanobacteria tree of life; these include unicellular, filamentous, nitrogen and non-nitrogen species. While genome reduction seems to be a trait shared amongst symbionts, the processes that lead to the establishment and integration of symbionts into their hosts are still unclear. Cyanobacteria are an ideal system to understanding how symbiosis has evolved because there are many taxa exhibiting a wide range of degrees of symbiotic integration. Additional shared features include fast protein evolution, a change in the CG content and increase in rates of evolution in relation to their closest relatives.

The aim is this study to investigate the timing and underlying genomic mechanisms driving cyanobacterial symbiosis in both nitrogen fixing and non-nitrogen fixing symbionts. This project will implement phylogenomics to reconstruct the evolutionary history and occurrences of symbiosis within cyanobacteria. A Bayesian approach will be implemented to determine age estimates for cyanobacteria symbiotic events. Comparative genomics will enable the identification of genes and gene families that have been lost during the process of symbiosis when involving examples of both nitrogen fixation and photosynthesis.

The Ph.D. student funded by this grant will also have the unique opportunity to not only collect the appropriate data but also to develop new phylogenetic methods. This is a great opportunity for students interested in photosynthesis, nitrogen fixation, evolutionary biology, phylogenetic methods, and bioinformatics. This is a four-year project funded by the Royal Society and hosted by the School of Geographical Sciences at the University of Bristol.