Ultrastructure of endogenous stages of Eimeria ninakohlyakimovae Yakimoff & Rastegaieff, 1930 Emend. Levine, 1961 in experimentally infected goat

Eimeria arloingi: further studies on the development of some endogenous stages

The present study investigated the ultrastructural characteristics of gamogony and oocyst wall formation of Eimeria arloingi in experimentally infected kids. The 18 newborn animals allocated to 3 equal groups. Two of groups, A, B were inoculated with a single dose of 1×10(3) and 1×10(5) sporulated oocysts of E. arloingi, respectively. At 7, 14, 21, 28, 35, and 42days postinoculation (DPI), 1 kid from each group was necropsied for ultrastructural studies. Transmission electron microscopy was used to screen for the presence of developmental stages of the parasite. All stages of microgametocyte and macrogametocyte developments and also oocyst wall formation were observed from 7 to 42DPI. Different stages of schizigony accompanied by marked proliferation of endoplasmic reticulum, mitochondria and several granular dividing nuclei were diagnosed in the affected epithelial cells. Young microgamonts were recognizable by an electron lucent parasitophorous vacuole and several dividing nuclei with prominent nucleolar and peripheral chromatin in the cytoplasm. At a later stage, the nuclei began to elongate and a single mitochondrion and two basal bodies were observed in close proximity nucleus. These bodies eventually protruded from the surface of the gametocyte and formed two flagellar structures. Up to 80-120 microgametes were produced per microgamont. Macrogamonts were recognized by the presence of wall-forming bodies of types 1 and 2. Electron lucent WFB2 appeared earlier than the electron denser WFB1 during the process of macrogametogenesis. The outer layer of the oocyst wall was formed by the release of the contents of WFB1 at the surface to form an electron dense layer. The WFB2 appeared, subsequently, to give rise to the electron lucent inner layer. WFB1 plays a major role in oocyst wall formation.

Nephromyces, a beneficial apicomplexan symbiont in marine animals

With malaria parasites (Plasmodium spp.), Toxoplasma, and many other species of medical and veterinary importance its iconic representatives, the protistan phylum Apicomplexa has long been defined as a group composed entirely of parasites and pathogens. We present here a report of a beneficial apicomplexan: the mutualistic marine endosymbiont Nephromyces. For more than a century, the peculiar structural and developmental features of Nephromyces, and its unusual habitat, have thwarted characterization of the phylogenetic affinities of this eukaryotic microbe. Using short-subunit ribosomal DNA (SSU rDNA) sequences as key evidence, with sequence identity confirmed by fluorescence in situ hybridization (FISH), we show that Nephromyces, originally classified as a chytrid fungus, is actually an apicomplexan. Inferences from rDNA data are further supported by the several apicomplexan-like structural features in Nephromyces, including especially the strong resemblance of Nephromyces infective stages to apicomplexan sporozoites. The striking emergence of the mutualistic Nephromyces from a quintessentially parasitic clade accentuates the promise of this organism, and the three-partner symbiosis of which it is a part, as a model for probing the factors underlying the evolution of mutualism, pathogenicity, and infectious disease.