Metabolic functions and inheritance of the microsporidian mitosome

Abstract

Microsporidia are a group of obligate intracellular parasites of economic and medical importance. Many aspects of microsporidian genomes and cell biology are a result of an extensive reductive evolution during adaptation to their intracellular parasitic lifestyle. Microsporidian mitochondrial homologues called mitosomes have only a single known conserved metabolic function in biosynthesis of the essential iron-sulfur clusters. Based on genomic data an additional function of the mitosome in the alternative respiratory pathway (ARP) was proposed for some microsporidians including human pathogenic Trachipleistophora hominis. This thesis provides the first direct experimental evidence for a mitosomal localization of the two components of the ARP in T. hominis. Quantitative analyses of the immunofluorescence data together with western blotting experiments provided results consistent with the life cycle-stage specific function of the organelle. In the proliferative stages of the T. hominis life cycle, capable of stealing ATP from the host, mitosomes seem to function mostly in the biosynthesis of the essential iron sulfur clusters. The ARP proteins are enriched in the T. hominis spores, which is consistent with the hypothetical functions of the mitosome in energy metabolism of the spore that is unable to rely on its host for ATP production. This thesis also provides the first bioinformatics characterization of the molecular machineries involved in the processes required for inheritance of the microsporidian mitosomes: organelle fission and segregation during the cell division. Specific antibodies were generated and used to detect the microsporidian spindle pole body (SPB), an organelle hypothesized to play a role in inheritance of the microsporidian mitosomes. Double labelling experiments using the specific antibodies against the SPB and mitosomal markers provide evidence for a stable connection between the two organelles throughout the life cycle of the parasite.