PhD Studentship: Self-Sabotage or Secret Advantage? The Biology of Fish Thiaminase

All animals require thiamine (vitamin B1) as an essential nutrient, yet many fish species paradoxically produce thiaminase enzymes that destroy it. Thiaminase activity has been linked to disease, reproductive failure, and population declines in fish-eating wildlife, but its biological function, regulation, and evolutionary origins remain poorly understood. This interdisciplinary PhD will explore the biological and environmental drivers of thiaminase production in fish, including the tissues and cell types involved, variation in thiaminase enzymes among species, and the influence of environmental conditions on thiaminase activity. Improved understanding of thiaminase biology will strengthen our ability to predict and manage thiamine deficiency events that threaten aquatic ecosystems. The project combines genomics, molecular biology, biochemistry, and experimental biology. The student will have the opportunity to employ a variety of techniques including single-cell transcriptomics to identify thiaminase-producing cells and tissues; comparative sequence and structural analyses to investigate enzyme evolution and function; development of improved approaches for measuring thiaminase activity; and experimental studies examining environmental regulation and physiological consequences of thiaminase expression. The student will have significant scope to direct the research programme, including selecting study species, identifying environmental variables, designing experiments, and pursuing emerging research questions. A major strength of the project is its interdisciplinary supervisory team: Dr Sarah Salisbury (fish genomics and single-cell RNA sequencing), Dr Ioanna Katsiadaki (fish physiology, ecotoxicology and welfare), Professor Nicholas Harmer (enzyme biochemistry and structural biology), and Dr Irene Cano Cejas (molecular biology and environmental genomics). Leveraging a strong and established Exeter-Cefas collaboration, the student will have access to complementary expertise, facilities, and mentoring across academic and government research environments while receiving hands-on training in bioinformatics, molecular laboratory techniques, protein modelling, experimental design, statistical analysis, scientific writing, and project management. This unique training environment will equip the student with highly transferable skills for careers across academia, industry and government.