Cytological and molecular description of Hamiltosporidium tvaerminnensis gen. et sp. nov., a microsporidian parasite of Daphnia magna, and establishment of Hamiltosporidium magnivora comb. nov.

We describe the new microsporidium Hamiltosporidium tvaerminnensis gen. et sp. nov. with an emphasis on its ultrastructural characteristics and phylogenetic position as inferred from the sequence data of SSU rDNA, alpha-and beta-tubulin. This parasite was previously identified as Octosporea bayeri Jirovec, 1936 and has become a model system to study the ecology, epidemiology, evolution and genomics of microsporidia - host interactions. Here, we present evidence that shows its differences from O. bayeri. Hamiltosporidium tvaerminnensis exclusively infects the adipose tissue, the ovaries and the hypodermis of Daphnia magna and is found only in host populations located in coastal rock pool populations in Finland and Sweden. Merogonial stages of H. tvaerminnensis have isolated nuclei; merozoites are formed by binary fission or by the cleaving of a plasmodium with a small number of nuclei. A sporogonial plasmodium with isolated nuclei yields 8 sporoblasts. Elongated spores are generated by the most finger-like plasmodia. The mature spores are polymorphic in shape and size. Most spores are pyriform (4.9-5.6x2.2-2.3 mu m) and have their polar filament arranged in 12-13 coils. A second, elongated spore type (6.8-12.0x1.6-2.1 mu m) is rod-shaped with blunt ends and measures 6.8-12.0x1.6-2.1 mu m. The envelope of the sporophorous vesicle is thin and fragile, formed at the beginning of the sporogony. Cytological and molecular comparisons with Flabelliforma magnivora, a parasite infecting the same tissues in the same host species, reveal that these two species are very closely related, yet distinct. Moreover, both cytological and molecular data indicate that these species are quite distant from F. montana, the type species of the genus Flabelliforma. We therefore propose that F. magnivora also be placed in Hamiltosporidium gen. nov

Mikrofotografie z RCH-mikroskopu digitálně zpracované pro počítačovou prezentaci

Živé bakterie, sinice, houby, prvoci, řasy, drobní živoč ichové a rostliny, popř. jejich vývojová stadia, jsou špatně pozorovatelní ve světelném mikroskopu z důvodu slabého vlastního zabarvení nebo blízkosti indexu lomu světla jejich těla indexu lomu prostředí (voda, fyziologický roztok, kultivační medium atd.)

RCH condenser (Relief contrast after Hostounský - application of Lambda Ltd. Praha) - samples of results with its use

An entirely novel method of optical microscopy in transmitted light "Relief Contrast after Hostounský" or RCH, Lambda Ltd. Praha, Czech Rebublic, was used to study of microorganisms, animal and plant cells as well as surface replicas or larger organissms. This equipment (special condenser) provides a three-dimensional image with higher contrast and resolution (up to two-fold)