Establishing Cryptosporidium parvum as a model organism

Cryptosporidium parvum is among the most common parasites in the known world and represents one of the leading causes of death among the immunocompromised. As an apicomplexan, C. parvum has many similarities to other globally important parasites such as Plasmodium falciparum and Toxoplasma gondii. Among these similarities are a complex life cycle and the ability to invade host cells. However, unlike most other apicomplexans, the cryptosporidia appear to have lost their namesake organelle, the apicoplast, and drastically reduced the size of their genome. For decades this caused issues in classifying the cryptosporidia. This has been potentially resolved, however, by recent phylogenetic studies that revealed a strong relationship between the cryptosporidia and the gregarines. The gregarines were parasites exclusively of invertebrates, until the reclassification to include the cryptosporidia. Though research into apicomplexan evolution and biology is still a nascent field, even less is known about the invertebrate portion. This is largely due to the lack of molecular tools and culturing techniques that are required to explore any organism beyond basic phylogenetics, in addition to their medical irrelevance prior to the inclusion of Cryptosporidium. Therefore, C. parvum represents a potential model organism for the gregarines and the evolutionary adaptations of apicomplexans from invertebrate to vertebrate hosts. It was the purpose of this thesis, therefore, to establish the tools and methodologies that would be required to begin developing C. parvum as such. To achieve this, first I successfully developed the world's first long-term culturing system of C. parvum, capable of maintain a live parasite culture for 60 days. Additionally, I developed novel methods of detecting and characterising the infection, including NMR based characterisation of infection metabolomes which also revealed a potentially more involved role for Taurine in the pathology of the infection. Furthermore, to demonstrate the power and applicability of this new system I produced the first experimental evidence for a functional ISC system within C. parvum. This also adds to a now growing list of non-canonical mitochondria containing organisms that still maintain an active mitochondrial Fe/S cluster biosynthetic pathway. In conclusion, this thesis represents a large step forward for both the C. parvum and gregarine fields and establishes many of the necessary techniques required for a new push in understanding these apicomplexans and their organelles.