The ultrastructural morphology of Eimeria tenella exhibits striking natural variation and undergoes significant changes during the first few hours of infection

Abstract

The data generated during this PhD provides novel insights into the biology of Eimeria parasites: protozoan organisms capable of causing enteric disease in a vast array of animals. Working with Eimeria tenella, a clinically and economically significant pathogen of chickens, I have quantified the fusion dynamics of the refractile bodies. Refractile bodies are non-membrane-bound organelles with immunogenic properties and unknown function. The structural and temporal dynamics of refractile body merger shares striking similarity with that of intrinsically disordered protein-containing droplet organelles; this comparison may help to direct future research into the character and function of these mysterious organelles. In an adjacent project, the organelle numbers and volumes for the E. tenella sporozoite stage were quantified. The resultant data shows a surprisingly high level of variability in cell morphometry; this could be due to genetic/epigenetic factors or may reflect an undiscovered maturation phase. The conoid is a cytoskeletal structure found in many important apicomplexan pathogens and is involved in host cell invasion and parasite motility. I have performed the first high resolution quantitative investigation of three-dimensional conoid structure and show that there is also a considerable level variability in conoid structure. Conoid fibre number was found to vary from 13 to 16 per conoid. This variation was seen in both freshly hatched and post-invasion sporozoites, suggesting that genetic factors are involved. Following analysis of structures within the conoid, my data suggests that secretory organelle protein release occurs through intra-conoidal transport, docking and fusion