Studies on the energy metabolism of Eimeria tenella and other coccidia
In this project I have undertaken an analysis of the enzymes and pathways of energy metabolism in Eimeria, with a particular view to determining how it is affected by, and adapted towards, the different environmental conditions encountered during its life cycle. The study has been dominated by two main approaches: characterisation of glycolytic enzymes, and analysis of end-products. In some areas it has been possible to carry out comparative studies using the related coccidial species Cryptosporidium parvum and Toxoplasma gondii. The activities of selected enzymes of energy metabolism were measured in an attempt to determine which pathways of energy metabolism were present in the parasites, and to asses their relative significance in different species and stages. Eimeria, Toxoplasma and Cryptosporidium all contained high levels of the glycolytic enzymes phosphofructokinase and pyruvate kinase, as well as lactate dehydrogenase. The TCA-specific enzyme succinate dehydrogenase could not be detected in Eimeria or Cryptosporidium but was present in tachyzoites of T. gondii. T. gondii and E. tenella contained an NADP+-specific isocitrate dehydrogenase but no NAD+-dependent enzyme; C. parvum contained neither isocitrate dehydrogenase variety. The activities of pyruvate kinase and lactate dehydrogenase were significantly higher in bradyzoites than in tachyzoites of T. gondii, suggesting that the former may be more reliant on fermentative modes of energy generation. In E. tenella, the enzyme activities investigated were generally much lower in sporulated than in unsporulated oocysts, probably reflecting the dormant nature of the latter. Sporozoites contained high levels of most enzymes indicating that significant activation or synthesis of enzymes occurs during, or shortly after, excystation.