Ultrastructural analysis of the sporozoite of Cryptosporidium parvum.

Cryopreparation of live sporozoites and oocysts of the apicomplexan parasite Cryptosporidium parvum, followed by transmission electron microscopy, was undertaken to show the 3D arrangement of organelles, their number and distribution. Profiles of parasites obtained from energy-filtering transmission electron microscopy of serial sections provided 3D reconstructions from which morphometric data and stereo images were derived. The results suggest that sporozoites have a single rhoptry containing an organized lamellar body, no mitochondria or conventional Golgi apparatus, and one or two crystalline bodies. Micronemes were shown to be spherical, numerous and apically located, and to account for 0.8% of the total cell volume. Dense granules were less numerous, larger, accounted for 5.8% of the cell volume, and were located more posteriorly than micronemes. A structure juxtaposed to the nucleus with similarities to the plastid-like organelle reported for other members of the Apicomplexa was observed. The detailed analysis illustrates the advantages of cryopreparation in retaining ultrastructural fidelity of labile or difficult to preserve structures such as the sporozoite of Cryptosporidium.

Heterologous expression of a basic elicitin from Phytophthora cryptogea in Phytophthora infestans increases its ability to cause leaf necrosis in tobacco.

The cry-b sequence, encoding a basic elicitin (cryptogein B) from Phytophthora cryptogea, was co-transformed into Phytophthora infestans. The copy number of the cry-b sequence varied in co-transformants. Nevertheless, in all cases the alien elicitin gene was transcribed, translated and the protein secreted in vitro from such transformants. Moreover, the secreted cryptogein B from P. infestans co-transformants increased their ability to cause a hypersensitive-response-like necrosis of tobacco leaves. It was thus concluded that the transfer of a single gene encoding a basic elicitin from one Phytophthora species to another can dramatically alter the phenotypic interaction of the transformed species with tobacco.