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Microsporidian diversity of the Pacific Northwest : microsporidiosis in a marine nematode Garcia, Alex Mauricio Ardila

Abstract

Microsporidia are a diverse group of spore-forming obligate endoparasitic fungi that have over 1,300 named species. Microsporidian spores are ubiquitous in the environment, but species diversity remains vastly unexplored, as the total number of species is suspected to equal that of their hosts. Microsporidian parasites are also model organisms for the study of genome reduction since they possess some of the smallest eukaryotic genomes known to date. To examine the diversity of microsporidian parasites in the environment, I screened for the presence of microsporidian parasites in poorly sampled reservoirs: soil, sand, and compost. I amplified ribosomal DNA (rDNA) sequences for 23 undescribed and three described microsporidian species that were highly diverse phylogenetically, including representatives from four of the five major microsporidian clades. Molecular screening for the hosts revealed that one undescribed microsporidian infected a free-living marine nematode (Odontophora rectangula). I characterized the infection and ultrastructure of the parasite by transmission electron microscopy and fluorescent in situ hybridization. It is a novel microsporidian that I named Sporanauta perivermis (“marine spore of roundworms”). S. perivermis infects the hypodermal, muscle, and reproductive tissues of adult O. rectangula. However, the infection pattern differed between genders where only reproductive tissues were infected in adult females (uteri and eggs), suggesting that S. perivermis is transmitted vertically. Juvenile hosts showed similar infection patterns to adults, and infection pattern allowed prediction of host gender prior to adulthood. Phylogenetic analyses revealed that S. perivermis is sister to a clade containing the Daphnia-infecting microsporidian Ordospora colligata and the Encephalitozoon lineage (five species), which contains three species that infect humans. A genomic survey of S. perivermis indicated high levels of similarity in gene content (over 90%), gene length, and synteny between S. perivermis, O. colligata and Encephalitozoon. S. perivermis and O. colligata shared chromosomal arrangements that were not present in Encephalitozoon genomes, including chromosomal rearrangements that could be linked to genome reduction mechanisms. The genome size of S. perivermis is at least 2.2 Mbp, but is likely larger since its intergenic regions were longer, on average, than those of relatives with genome sizes of 2.3-3.0 Mbp.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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