Investigating the diversity, adaptations and potential roles of Blastocystis in the gut

Blastocystis is ubiquitously distributed coloniser of the gastrointestinal tract. To date, 17 subtypes and other isolates have been characterised from a range of invertebrate and vertebrate hosts, including humans. Despite current knowledge regarding its prevalence, diversity and associations with the gut microbiota, there is still uncertainty about its role as a pathogen. Herein, I aimed to explore the diversity of Blastocystis and investigate its role(s) in the gut using a multiphasic approach, combining culturomics, with molecular biology, phylogenetics, metagenomics, transcriptomics, and metabolomics. This allowed for an investigation of not only the prevalence of Blastocystis, but aided in the exploration of its in vivo and in vitro function.Results from my thesis demonstrate that Blastocystis had a high incidence in asymptomatic captive animals, with an excess of 40% in the species sampled. Additionally, numerous novel hosts were identified, while showing that co-infection with other microbial eukaryotes was relatively frequent. Bacterial community profiling of Blastocystis positive animals demonstrated no overall changes to bacterial diversity, but highlighted a number of taxa that were associated with Blastocystis colonisation. In vitro and in vivo NMR metabolomics further revealed a distinct metabolome in positive individuals. Here, a number of metabolites linked to eubiosis were identified including l-arginine, l-glutamine and propanoate. Lastly, treatment of Blastocystis with oxygen revealed a number of pathways possibly implicated in oxygen stress responses.As a result, my Ph.D work provides a steppingstone to understand the prevalence of Blastocystis and the role of this questionable gut "parasite" in health and disease in both animals and humans.