Prospective enzymes for omega-3 PUFA biosynthesis found in endoparasitic classes within the phylum Platyhelminthes.

The free-living infectious stages of macroparasites, specifically, the cercariae of trematodes (flatworms), are likely to be significant (albeit underappreciated) vectors of nutritionally important polyunsaturated fatty acids (PUFA) to consumers within aquatic food webs, and other macroparasites could serve similar roles. In the context of de novo omega-3 (n-3) PUFA biosynthesis, it was thought that most animals lack the fatty acid (FA) desaturase enzymes that convert stearic acid (18:0) into ɑ-linolenic acid (ALA; 18:3n-3), the main FA precursor for n-3 long-chain PUFA. Recently, novel sequences of these enzymes were recovered from 80 species from six invertebrate phyla, with experimental confirmation of gene function in five phyla. Given this wide distribution, and the unusual attributes of flatworm genomes, we conducted an additional search for genes for de novo n-3 PUFA in the phylum Platyhelminthes. Searches with experimentally confirmed sequences from Rotifera recovered nine relevant FA desaturase sequences from eight species in four genera in the two exclusively endoparasite classes (Trematoda and Cestoda). These results could indicate adaptations of these particular parasite species, or may reflect the uneven taxonomic coverage of sequence databases. Although additional genomic data and, particularly, experimental study of gene functionality are important future validation steps, our results indicate endoparasitic platyhelminths may have enzymes for de novo n-3 PUFA biosynthesis, thereby contributing to global PUFA production, but also representing a potential target for clinical antihelmintic applications.

Fatty acid composition of cold-adapted carotenogenic basidiomycetous yeasts.

We studied fatty acids (FAs) profiles in six carotenoid-producing yeast species isolated from temperate aquatic environments in Patagonia. Total FAs ranged from 2 to 15% of dry biomass. Linoleic, oleic, palmitic and alpha-linolenic acids were the major FAs constituents, which accounted for as much as 40%, 34%, 13% and 9% of total FAs, respectively. The proportion of each FA varied markedly depending on the taxonomic affiliation of the yeast species and on the culture media used. The high percentage of polyunsaturated fatty acids (PUFAs) found in Patagonian yeasts, in comparison to other yeasts, is indicative of their cold-adapted metabolism. Our results suggest that Patagonian yeasts may be considered an interesting source of essential PUFAs.

Effect of temperature on the fatty acid composition and temporal trajectories of fatty acids in fasting Daphnia pulex (Crustacea, Cladocera).

Poikilothermic organisms accumulate highly unsaturated FA (HUFA) in their lipids at reduced temperatures to maintain cell membrane fluidity. In this study we investigated the effect of temperature on temporal trajectories of FA of fasting Daphnia pulex cultured on a HUFA-free diet. Daphnia pulex populations were maintained for 1 mon at 22 and 11 degrees C and were fed the chlorophyte Ankistrodesmus falcatus. We observed conversion of C18 FA precursors to EPA (20:5n3) and arachidonic acid (ARA; 20:4n6) in D. pulex. We showed that long-term exposure to cold temperature causes a significant increase in EPA. HUFA such as ARA and EPA are highly conserved during starvation. Therefore, D. pulex has the biosynthetic capacity to adjust and to maintain the content of HUFA required to survive at low temperatures.

Use of water clarity to monitor the effects of climate change and other stressors on oligotrophic lakes.

We present evidence from studies of lakes in Killarney Park, Ontario, Canada that water clarity is a key variable for monitoring the effects of climate change, high UV exposure and acidification. In small oligotrophic lakes, these stressors affect water clarity primarily by altering the concentration of DOC in lake water. Clear lakes (<2 mg L(-1) DOC) proved to be highly sensitive indicators of stressors, exhibiting large thermal and optical responses to small changes in DOC. Extremely clear (<0.5 mg L(-1) DOC) acidic lakes showed the effects of climate change and solar bleaching in recent decades. These lakes became much clearer even though they were slowly recovering from acidification.

Tandem mass spectrometry of herbicide residues in lipid-rich tissue.

A tandem mass spectrometry procedure, originally developed for bacterial biofilms was adapted for the identification of herbicide residues in lipid-rich tissue of amphipods collected from microcosms in a prairie wetland. For this application, the amounts of tissue employed (less than 1 mg wet weight), and detection of target analytes at picogram levels, were similar to the values reported for bacterial biofilms. Described is an application of the technique for the identification of residues of the herbicide S-2,3,3-trichloroallyl diisopropyl thiocarbamate (triallate; trade name Avadex-BW). For amphipods collected from microcosms exposed to the herbicide 2-[4-(2,4-dichlorophenoxy)phenoxy]propionic acid methyl ester (diclofop-methyl, trade name Hoe Grass), there were detectable levels of only the hydrolysis product, diclofop acid, in the lipid-rich tissue. Other transformation products reported for bacterial biofilms were not observed in the amphipods.

Spatial and temporal variability in lipid dynamics of common amphipods: assessing the potential for uptake of lipophilic contaminants.

: A three-tiered approach involving autoradiography, measurement of seasonal lipid patterns and deployment of in situ microcosms, was used to assess the potential of the moderately lipophilic herbicide triallate to accumulate in two amphipod species (Hyalella azteca and Gammarus lacustris) in two prairie lakes and one prairie pond. Autoradiography revealed that the storage sites for triallate in amphipod tissues were associated with lipid-rich tissues, in particular, with triacylglycerol storage sites and the nervous system. Seasonal lipid patterns (total lipid) of amphipods did not differ amongst sites within a waterbody, however, there were marked differences amongst water bodies. Female amphipods had higher lipid contents than males during the reproductive period in early summer but this difference diminished later in the summer. Bioaccumulation factors of triallate in amphipod tissues ranged from 72 to 80 times the nominal water concentrations in 7 day microcosm trials. Triacylglycerol content and triallate body burden were positively correlated (r (2)=0.58-0.91) for H. azteca in the two lakes in which the microcosms were deployed. However, no significant correlations were obtained between triacylglycerol content and triallate body burden for G. lacustris. Triacylglycerol contents in the amphipods were generally highest in spring and autumn, coinciding with application times for triallate.

The influence of environmental factors on seasonal changes in bacterial cell volume in two prairie saline lakes.

Bacterial biovolumes of hypertrophic Humboldt Lake (total dissolved solids = 3.3 g liter(-1); 6 m deep) and oligotrophic Redberry Lake (total dissolved solids = 20.9 g liter(-1); 17 m deep), Saskatchewan, were measured concurrently with a variety of environmental variables to identify the major factors correlated with volume changes. There was no difference (P > 0.05) in mean bacterial volume between Redberry Lake (0.084 ± 0.034 µm(3) SD) and Humboldt Lake (0.083 ± 0.021 µm(3) SD). Statistical analyses suggested there were marked differences in the factors associated with the pronounced seasonality of bacterial cell volumes in these two lakes. Variance in bacterial volume in the epilimnion of Redberry Lake was best explained by a multivariate regression model which included ciliate abundance and chlorophyll concentration (r (2) = 0.96). The model accounting for changes in hypolimnetic bacterial volume included ciliate numbers and primary production (r (2) = 0.94), of the measured variables. Bacterial volume in Humboldt Lake was most highly correlated with primary production (r (2) = 0.59). Bacterial production (estimated as the rate of thymidine incorporation into DNA) and growth (thymidine incorporation rate normalized to cell numbers) were not correlated to cell volume, with the exception of cocci volume in Humboldt Lake.