Ultrastructure and molecular phylogeny of Anisofilariata chironomi g.n. sp.n. (Microsporidia: Terresporidia) from Chironomus plumosus L. (Diptera: Chironomidae)

Abstract

Larvae of Chironomus plumosus, collected in North-Western Russia in September 2008, were infected with a microsporidium possessing broadly oval uninucleate spores in sporophorous vesicles. Sporogony and spore ultrastructure of this microsporidium differed from that of known microsporidian species, suggesting establishment of a new species, Anisofilariata chironomi, being a type species of a new genus. Sporogony di-, tetra-, octo-, and 16-sporoblastic. Fixed and stained spores are 4.7-6.8 x 3.4-5.4 microm in size, the spore measurements varying depending upon the number of spores in the sporophorous vesicle. The polaroplast is bipartite, with anterior and posterior parts composed of very thin and thick lamellae, respectively, and occupies the major volume of the spore. The polar filament is anisofilar, with two broad proximal and 10-13 narrow distal coils arranged in 2-4 layers. The sporophorous vesicle is bounded by a thin membrane and contains multiple tubular structures. Small subunit ribosomal DNA phylogeny showed basal position of the new microsporidium to a cluster uniting microsporidia infecting ciliates (Euplotespora binucleata), microcrustaceans (Glugoides intestinalis, Mrazekia macrocyclopis), lepidopteran insects (Cystosporogenes spp., Endoreticulatus spp.) and human (Vittaforma corneae), nested within Clade IV sensu Vossbrinck and Debrunner-Vossbrinck (2005 Folia Parasitol 52:131-142). No close phylogenetic relationships were found between A. chironomi and microsporidia from other dipteran hosts.