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.     

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.     

Galleria melonella as an experimental in vivo host model for the fish-pathogenic oomycete Saprolegnia parasitica

Oomycetes are eukaryotic pathogens infecting animals and plants. Amongst them Saprolegnia parasitica is a fish pathogenic oomycete causing devastating losses in the aquaculture industry. To secure fish supply, new drugs are in high demand and since fish experiments are time consuming, expensive and involve animal welfare issues the search for adequate model systems is essential. Galleria mellonella serves as a heterologous host model for bacterial and fungal infections. This study extends the use of G. mellonella for studying infections with oomycetes. Saprolegniales are highly pathogenic to the insects while in contrast, the plant pathogen Phytophthora infestans showed no pathogenicity. Melanisation of hyphae below the cuticle allowed direct macroscopic monitoring of disease progression. However, the melanin response is not systemic as for other pathogens but instead is very local. The mortality of the larvae is dose-dependent and can be induced by cysts or regenerating protoplasts as an alternative source of inoculation.     

Phytoalexin resveratrol attenuates the mutagenicity of the heterocyclic amines 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline

Resveratrol is a phytoalexin, that belongs to a family of naturally occurring stilbenes. It has been reported that resveratrol can inhibit chemical carcinogenesis in experimental animals and although the mechanisms involved are unknown, an anti-mutagen mechanism has been proposed. We have explored this hypothesis using mutagenicity assays based on bacterial (Salmonella typhimurium) and eukaryotic cells (Chinese hamster V79 cells). We found resveratrol to be potent in both systems, blocking the mutagenicity of the food-derived heterocyclic amines (HA) 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) at micromolar concentrations. Furthermore, in cells capable of activating 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine to cytotoxic derivatives, resveratrol was able to attenuate cytotoxicity. Paradoxically, in cells lacking the ability to activate PhIP, resveratrol itself was toxic and co-incubation with PhIP reduced this toxicity. Our data confirm the potent anti-mutagenic activity of resveratrol and support its potential as a chemopreventative.