Ultrastructure, chromosomal karyotype, and molecular phylogeny of a new isolate of microsporidian Vairimorpha sp. BM (Microsporidia, Nosematidae) from Bombyx mori in China.

The spore morphology, chromosomal karyotype, and molecular systematic of a new microsporidian which was isolated from the domesticated silkworm Bombyx mori (Lepidoptera: Bombycidae) in Shandong, China have been studied. The spores were long oval and measured 3.4 × 1.6 μm on fresh smears. Ultrastructure of the spores was characteristic for the genus Vairimorpha: 13-15 polar filament coils, posterior vacuole, and a diplokaryon. Six chromosome bands have been separated by pulsed field gel electrophoresis. The sequenced complete rRNA gene of this isolate is 4,231 bp long. Phylogenetic analysis based on SSU rRNA gene and LSU rRNA gene both revealed that this novel microsporidian which was isolated from B. mori had close relationship to the genus Vairimorpha, not to the genus Nosema. Moreover, the organization of the rRNA units of this microsporidian is not similar to that of Nosema bombycis, but same to that of other microsporidian, such as Vairimorpha necatrix. Although this microsporidian, designed as Vairimorpha sp. BM, was isolated from B. mori, all of these informations indicate that this isolate is closely related to the Vairimorpha group.