BSSP 1999 Spring Meeting - Posters

The mitochondrial Hsp70 gene of Entamoeba histolytica

Christina Bakatselou. London School of Hygiene and Tropical Medicine.

Until recently it was believed that Entamoeba histolytica belongs to an early branching eukaryotic lineage, as it lacks typical organelles such as mitochondria, peroxisomes, rough endoplasmic reticulum and Golgi dictyosomes and has an unusual glycolytic metabolism. However, ribosomal RNA-based phylogenetic trees have shown that E.histolytica branches more recently than several lineages with typical eukaryotic organelles and metabolism.Evidence of secondary loss of mitochondrial function in Entamoeba histolytica has been obtained by cloning of genes that encode proteins which in other organisms are found in the mitochondrion, i.e. pyridine nucleotide transhydrogenase (PNT) and the mitochondrial chaperonin cpn60 genes.We have now isolated a gene encoding a mitochondrial-like Hsp70 homologue from E.histolytica. cDNA and genomic library clones have been isolated and sequenced. Comparison with previously published sequences confirms the assumption that E.histolytica comes from mitochondrion - bearing ancestors.Southern blotting revealed that there is one copy of the gene and Northern blots after heat shock showed that expression of the hsp70 mRNA is probably independent of thermal stress. Preliminary phylogenetic analysis will also be presented.

In Situ Biodegradation in Organically-Contaminated Aquifers: How Important are Protists?

G. Novarino1, A. Warren* and N.E. Kinner**. *Department of Zoology, Natural History Museum. **Environmental Research Group, Department of Civil Engineering, University of New Hampshire, USA.

Subsurface protistan populations are mostly composed of heterotrophic nanoflagellates. In pristine, uncontaminated aquifers flagellate population densities are typically low. By contrast, in organically-contaminated aquifers they may reach about 10⁵ cells per gram dry weight of aquifer material. Aquifer flagellates are mostly bacterivorous and frequently associate with sediment particles, known to harbour abundant bacterial populations which may be capable of biodegradation processes. Recently, bacterial grazing by subsurface protists has been shown to have a significant effect on the rate of in-situ biodegradation of trichloroethylene. This corroborates earlier reports that aquifer flagellates may be used as indicators of in-situ biodegradation. Although preliminary evidence suggests that the aquifer flagellates do not directly ingest a significant proportion of large molecular weight organic compounds, we also hypothesize that flagellates may be directly involved in biodegradation processes.

Flagellate participation in the microbial food webs of epilithic biofilms in upland streams.

AP Hunt, J Hamilton-Taylor and J. Parry. Division of Biological Sciences, I.E.N.S., Lancaster University, Lancaster, UK.

Diel feeding patterns in four Chrysophyte flagellates

Jo Alabaster, Stephanie Hodge and Diane Purcell. Centre for Population Biology, Imperial College.

Mixotrophic algae are ones that are capable of heterotrophic nutrition. If cells feed on bacteria as a supplement to photosynthesis, then ingestion may be expected to increase at night. For non-photosynthetic mixotrophs, it may be expected that feeding rate will be constant. Ochromonas sp., Dinobryon sp., Paraphysomonas imperforata and Anthophysa vegetans represent the spectrum of dependence on heterotrophy; Ochromonas sp. and Dinobryon sp. are photosynthetic, whereas P. imperforata and A. vegetans are entirely heterotrophic. P. imperforata has no chloroplast remnants but A. vegetans cells contain a photoreceptor. All cultures were kept at 40 µmol m^-2 s^-1 light intensity with a 16/8 h light/dark cycle (dark from 22:00-06:00 h) at 15^o C and fed mixed species of pond bacteria. Ingestion rates of live cells were measured by feeding samples with fluorescently labelled, dead pond bacteria. The number of bacteria present inside algal cells was counted under UV light over a 10 min or 40 min (Dinobryon sp.) time course. Feeding rates were measured three times every hour for twenty-four hours for each species. All species showed variation in feeding rate over the twenty-four hour period. Ochromonas sp. showed increased feeding during the dark period. Dinobryon sp. had two peaks of ingestion at 7am and 8pm.