Protein synthesis in the plastid of Plasmodium falciparum.

The plastid organelle of malarial and other apicomplexan parasites contains ribosome-like particles as well as a genome dedicated largely to specifying components of a protein expression system. We have identified plastid ribosomes using hybridization studies and show that in erythrocytic stages of Plasmodium falciparum a subset of polysomes carries plastid-specified rRNAs and mRNA, supporting the idea that protein synthesis is active in the plastid.     

Ecology of testate amoebae (Protozoa: Rhizopoda) on peatlands in western Russia with special attention to niche separation in closely related taxa.

Testate amoebae (Protozoa: Rhizopoda) are frequently used as indicators of past environmental changes, and the interpretation of fossil assemblages depends upon our knowledge of ecological affinities of taxa in modern environments. A variety of taxonomic approaches have been used in fossil studies, mostly involving grouping of closely related taxa. This paper presents data from peatlands in western Russia relating surface wetness parameters to species occurrence. Relationships between species abundance, water table depth and soil moisture are modelled using weighted averaging, and species niches are calculated as optima and tolerance for these parameters. Niche separation of closely related taxa is examined in detail and it is shown that there is often a gradient of hydrological preference within each group of taxa. Wet to dry gradients include those found in the Trigonopyxis arcula group (T. arcula var. major > T. arcula > T. minuta), the Assulina-Valkanovia group (A. seminulum > A. muscorum > V. elegans), and the Trinema lineare group (T. lineare var. truncatum/ T. lineare > T. lineare var. terricola), all of which are associated with a large to small size gradient. In addition, spined forms within the Euglypha and Placocista genera are shown to consistently occur in wetter habitats than glabrous forms or those with shorter spines. It is concluded that palaeoecological studies should attempt the lowest taxonomic divisions possible within these groups, to maximise the ecological indicator value of the assemblages recorded.     

Protozoal sequences may reveal additional isoforms of the 14-3-3 protein family

The phylogenetic position of eleven 14-3-3 proteins from five protozoal species was tested relative to other eukaryotic 14-3-3 versions representing many of the previously described isoforms. The protozoal proteins, four from Entodinium caudatum, three from Entameoba histolytica and four from apicomplexan parasites formed clusters closer to the plant and animal epsilon isoforms than to the animal beta, gamma/eta, sigma/theta, and zeta isoforms. This extends the preliminary findings of Wang and Shakes (1996) but data from a wider range of genera are still required to strengthen our hypothesis that the protozoan isoforms may constitute novel isoforms of the 14-3-3 family.     

Antibiotic inhibitors of organellar protein synthesis in Plasmodium falciparum.

Elongation factor Tu (EF-Tu) is encoded by the tuf gene of the plastid organelle of the malaria parasite Plasmodium falciparum. A range of structurally unrelated inhibitors of this GTP-dependent translation factor was shown to have antimalarial activity in blood cultures. The most active was the cyclic thiazolyl peptide amythiamicin A with an IC50 = 0.01 microM. Demonstrable complexes were formed in vitro between a recombinant version of P. falciparum EF-Tu(pl) and inhibitors that bind to different sites on EF-Tu; these included the antibiotics kirromycin, GE2270A and enacyloxin IIa.     

V-ATPase is a major component of the Golgi complex in the scaly green flagellate Scherffelia dubia

Highly purified membranes isolated from the Golgi complex of the scaly green flagellate Scherffelia dubia (Chlorophyta) were subjected to Triton X-114 two-phase partitioning. Proteins in the detergent phase were analyzed by 2D gel electrophoresis and a major protein of 66 kD (p66) was N-terminally sequenced. The complete cDNA sequence of p66 was obtained by 3' RACE-PCR and screening of a cDNA library of S. dubia with a PCR probe derived from the 3' RACE. Sequence analysis of the cDNA clone identified p66 as subunit A of V-ATPase. Other major proteins in the isolated Golgi complex were immunoreactive to heterologous antibodies raised against subunit B or the holoenzyme of V-ATPase. A polyclonal (anti-p66) antibody raised against a recombinant, bacterially expressed p66 fusion protein recognized p66 in the isolated Golgi complex in western blots and localized the antigen by immunogold electron microscopy mostly to the scale reticulum but also to the Golgi stack within the Golgi complex. Concanamycin A-sensitive (but bafilomycin A1-insensitive) ATPase activity was present in the isolated Golgi complex, and monensin at 0.5-1 microM reversibly inhibited flagellar regeneration and resulted in swelling of Golgi cisternae. It is concluded that a functional V-ATPase is a major protein of the Golgi complex in S. dubia and is presumably associated with sorting processes at the endocytotic/exocytotic boundary of the Golgi complex.     

Characterization of Hemiselmis amylosa sp. nov. and phylogenetic placement of the blue-green cryptomonads H. amylosa and Falcomonas daucoides

The morphology and ultrastructure of a new freshwater blue-green cryptomonad, Hemiselmis amylosa sp. nov., is described. In addition, a marine blue-green cryptomonad isolate was confirmed as Falcomonas daucoides by electron microscopy and phycobilin analysis so that it could be included in molecular sequence studies, since the original isolate is no longer available. Complete ssu rRNA gene sequences for H. amylosa and F. daucoides were obtained. Our freshwater isolate of Hemiselmis possesses the same general features described for blue-green marine species, but it differs in having an eyespot, and multiple, single thylakoids penetrating the pyrenoid; therefore, a new blue-green, freshwater species is described. Phylogenetic analyses of H. amylosa and F. daucoides, as well as 24 other cryptophyte algae, indicate a monophyletic origin for all blue-green cryptomonads. Falcomonas forms a sister clade to blue-green cryptomonads, indicating that it is the most primitive extant blue-green cryptomonad and probably diverged early from other blue-green genera. Furthermore, we suggest that the eocyte blue-green cryptomonad may have originated from a Proteomonas-like progenitor that underwent a pigment change, resulting in a Falcomonas-like cell. Based on comparative morphology, the Proteomonas haplomorph may be a likely candidate in the evolutionary transformation from red to blue-green in cryptomonads; however, phylogenetic analyses neither support nor refute this hypothesis. Finally, the current status of cryptomonad classification is addressed.     

Systematics of the enigmatic kathablepharids, including EM characterization of the type species, Kathablepharis phoenikoston, and new observations on K. remigera comb.nov

The colorless flagellate Kathablepharis has consisted of five species based on light microscopic studies, and the ultrastructure of the type species, Kathablepharis phoenikoston, is described for the first time. The heterotrophic, marine flagellate Leucocryptos consisted of two species, but additional ultrastructural details for one of these, Kathablepharis remigera comb. nov. (= Leucocryptos remigera V?rs), indicates that it should be transferred to Kathablepharis. The cellular structure of these two species is similar to previously studied kathablepharids. However, there is variation in the feeding apparatus and cytoskeleton. The feeding apparatus of both species has a cytostome, a cytostomal ring, and cytopharyngeal rings. The cytoskeleton consists of inner microtubular arrays and outer or sub-pellicular microtubular arrays. In addition, several features of the flagellar apparatus are described for K. phoenikoston and K. remigera. The ultrastructure of these two species is compared with other kathablepharids to evaluate their taxonomy and phylogeny. We classify Kathablepharis and Leucocryptos in the family Kathablepharididae incertae sedis.