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Hypothesis on the origin of Sporozoa from Spiromonadida ancestors is discussed on the basis of the data on their ultrastructure. The phylum Sporozoa comprises three large distinct groups of organisms as follows: Perkinsemorpha, Gregarinomorpha and Coccidiomorpha. Advanced Coccidiomorpha have not descended directly from Gregarinomorpha. Gregarinomorpha and Coccidiomorpha have common ancestors, Protospiromonadida. Heteroxeny is quite common among Coccidiomorpha. The formation of heteroxeny in Coccidiomorpha proceeded in different ways and at different time in different groups. Cystoisospora, Toxoplasma, Aggregata, Atoxoplasma, Schellackia have primary definitive hosts while Sarcocystis, Karyolysus, Haemogregarina, Hepatozoon, Plasmodium, Haemaproteus, Leucocytozoon, Akiba, Babesiosoma, Theileria, Babesia have primary intermediate hosts.
The paper presents a survey of literary and author's own data on metabolism of nitric bases, nucleosides and orotic acid in Eimeria, Toxoplasma and Plasmodium. Experimental data on nucleotide content of DNA, fractional content of ribosome RNA, isofermental spectrum of a number of oxidation-reduction enzymes and immunochemical analysis of antigens in various groups of Sporozoa (Eimeria, Toxoplasma and Plasmodium) are given. A possible use of biochemical and immunochemical data for the taxonomy of Sporozoa is suggested.
The effect of three polyether antibiotics (monensin, salinomycin, lasalocid) on developmental stages of Eimeria tenella (Coccidia, Sporozoa) was studied in vivo and in vitro by means of light and electron microscopy. It was found that these three drugs act against free merozoites, which are destroyed by bursting of the cell border (i.e. pellicle), endoplasmic reticulum and internal organelles even after very short exposure times (20 min) in media containing 1 ppm, 10 ppm or 100 ppm of these drugs. Sporozoites, however, survived these drug concentrations during an exposure time of 30 min (this would be sufficient to penetrate host cells and start development). Intracellular stages, which were situated in a parasitophorous vacuole within an intact host cell, were not attacked, apparently because these drugs are almost incapable of penetrating host cells. On the other hand, parasites (such as differentiated schizonts, gamonts) located within degenerating host cells showed slight disintegration, which did not necessarily led to their death. From these results it becomes clear why these polyether antibiotics have to be fed daily. Doses of 70 ppm salinomycin, 125 ppm monensin and 125 ppm lasalocid were found to bring about an equivalent protective effect against an infection with 40,000 Eimeria tenella oocysts.
Analysis of peculiarities in organization and functioning of metabolic ways of biosynthesis of purine and pyrimidine nucleotides in representatives of Sporozoa type has shown that molecular aftereffects of adaptation to intracellular parasitism in unicellular eukaryotes consists in the increase in the level of molecular organization, loss of some metabolic path ways and some enzymes, origin of a new metabolic system, a host-parasite one. Functioning of this system is achieved due to developing by the parasite mechanisms that are similar to the host's ones.
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We present an evolutionary analysis of 13 species of Sarcocystis, including 4 newly sequenced species with ruminants as their intermediate host, based on complete small subunit rDNA sequences. Those species with ruminants as their intermediate host form a well-supported clade, and there are at least two major clades within this group, one containing those species forming microcysts and with dogs as their definitive host and the other containing those species forming macrocysts and with cats as their definitive host. Those species with nonruminants as their intermediate host form the paraphyletic sister group to these clades. Most of the species have considerable genotypic differences (differing in more than 100 nucleotide positions), except for S. buffalonis and S. hirsuta. There is a large suite of genotypic differences indicating that those species infecting ruminant and nonruminant hosts have had very different evolutionary histories, and similarly for the felid- and canid-infecting species. Furthermore, the rDNA sequences that represent the different structural regions of the rRNA molecule have very different genotypic behavior within Sarcocystis. The evolution of these regions should be functionally constrained, and their differences can be explained in terms of the importance of the nucleotide sequences to their functions.
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