Phytoplankton group identification with chemotaxonomic biomarkers: In combination they do better.

Chemotaxonomic biomarkers are needed to monitor and evaluate the nutritional quality of phytoplankton communities. The biomolecules produced by different phytoplankton species do not always follow genetic phylogeny. Therefore, we analyzed fatty acids, sterols, and carotenoids from 57 freshwater phytoplankton strains to evaluate the usability of these biomolecules as chemotaxonomic biomarkers. We found 29 fatty acids, 34 sterols, and 26 carotenoids in our samples. The strains were grouped into cryptomonads, cyanobacteria, diatoms, dinoflagellates, golden algae, green algae, and raphidophytes, and the phytoplankton group explained 61%, 54%, and 89% of the variability of fatty acids, sterols, and carotenoids, respectively. Fatty acid and carotenoid profiles distinguished most phytoplankton groups, but not flawlessly. For example, fatty acids could not distinguish golden algae and cryptomonads, whereas carotenoids did not separate diatoms and golden algae. The sterol composition was heterogeneous but seemed to be useful for distinguishing different genera within a phytoplankton group. The chemotaxonomy biomarkers yielded optimal genetic phylogeny when the fatty acids, sterols, and carotenoids were used together in multivariate statistical analysis. Our results suggest that the accuracy of phytoplankton composition modeling could be enhanced by combining these three biomolecule groups.

Tracing the fate of microplastic carbon in the aquatic food web by compound-specific isotope analysis.

Increasing abundance of microplastics (MP) in marine and freshwaters is currently one of the greatest environmental concerns. Since plastics are fairly resistant to chemical decomposition, breakdown and reutilization of MP carbon complexes requires microbial activity. Currently, only a few microbial isolates have been shown to degrade MPs, and direct measurements of the fate of the MP carbon are still lacking. We used compound-specific isotope analysis to track the fate of fully labelled 13C-polyethylene (PE) MP carbon across the aquatic microbial-animal interface. Isotopic values of respired CO2 and membrane lipids showed that MP carbon was partly mineralized and partly used for cell growth. Microbial mineralization and assimilation of PE-MP carbon was most active when inoculated microbes were obtained from highly humic waters, which contain recalcitrant substrate sources. Mixotrophic algae (Cryptomonas sp.) and herbivorous zooplankton (Daphnia magna) used microbial mediated PE-MP carbon in their cell membrane fatty acids. Moreover, heteronanoflagellates and mixotrophic algae sequestered MP carbon for synthesizing essential ω-6 and ω-3 polyunsaturated fatty acids. Thus, this study demonstrates that aquatic micro-organisms can produce, biochemically upgrade, and trophically transfer nutritionally important biomolecules from PE-MP.

Lake eutrophication and brownification downgrade availability and transfer of essential fatty acids for human consumption.

Fish are an important source of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) for birds, mammals and humans. In aquatic food webs, these highly unsaturated fatty acids (HUFA) are essential for many physiological processes and mainly synthetized by distinct phytoplankton taxa. Consumers at different trophic levels obtain essential fatty acids from their diet because they cannot produce these sufficiently de novo. Here, we evaluated how the increase in phosphorus concentration (eutrophication) or terrestrial organic matter inputs (brownification) change EPA and DHA content in the phytoplankton. Then, we evaluated whether these changes can be seen in the EPA and DHA content of piscivorous European perch (Perca fluviatilis), which is a widely distributed species and commonly consumed by humans. Data from 713 lakes showed statistically significant differences in the abundance of EPA- and DHA-synthesizing phytoplankton as well as in the concentrations and content of these essential fatty acids among oligo-mesotrophic, eutrophic and dystrophic lakes. The EPA and DHA content of phytoplankton biomass (mgHUFAg-1) was significantly lower in the eutrophic lakes than in the oligo-mesotrophic or dystrophic lakes. We found a strong significant correlation between the DHA content in the muscle of piscivorous perch and phytoplankton DHA content (r=0.85) as well with the contribution of DHA-synthesizing phytoplankton taxa (r=0.83). Among all DHA-synthesizing phytoplankton this correlation was the strongest with the dinoflagellates (r=0.74) and chrysophytes (r=0.70). Accordingly, the EPA+DHA content of perch muscle decreased with increasing total phosphorus (r2=0.80) and dissolved organic carbon concentration (r2=0.83) in the lakes. Our results suggest that although eutrophication generally increase biomass production across different trophic levels, the high proportion of low-quality primary producers reduce EPA and DHA content in the food web up to predatory fish. Ultimately, it seems that lake eutrophication and brownification decrease the nutritional quality of fish for human consumers.

Characterization of a novel transgenic rat carrying human tau with mutation P301L.

We have established a novel transgenic rat line carrying human microtubule-associated protein Tau-40 with mutation P301L. hTau-40/P301L transgenic male and female rats were followed up to 2 years of age. The hTau-40/P301L rats expressed human tau mRNA and protein in the limbic cortex and associated white matter, hippocampus and spinal cord. With increasing age, the staining density for phosphorylated tau increased in all these areas. Neither silver stains nor Fluoro-Jade staining indicated the presence of dying neurons, or axonal degeneration, and there was no evidence of increased gliosis or inflammation. However, some neurons did display dendritic abnormalities, and immunoblots revealed the presence of sarcosyl insoluble tau. A large test battery revealed no behavioral abnormalities in these rats, except a mild hyperactivity in the elevated plus maze. In conclusion, this transgenic tau rat may be a useful model for 'pretangle' pathology, although in this study conditions were not sufficient to induce significant neuronal loss or behavioral deficits.

Electrospray ionization and collision-induced dissociation time-of-flight mass spectrometry of neutral glycosphingolipids.

A series of native naturally occurring neutral glycosphingolipids has been analysed by electrospray ionization tandem mass spectrometry using a hybrid magnetic sector-TOF instrument. The collision-induced dissociation products of precursor ions were detected by an orthogonal acceleration time-of-flight mass spectrometer as the second analyser. Glycosphingolipids, with mono- to hexa-saccharide chain lengths with different ceramide constituents, were studied. The result of electrospray ionization in the positive ion mode generally showed singly charged molecular ions with Na+ as adduct, [M + Na]+. The sensitivity of the electrospray ionization was greatly enhanced by addition of NaCl, LiCl (forming [M + Li]+) or KCl (yielding [M + K]+) to the sample. A comparison between the collision-induced dissociation of precursor molecular ions of monoglycosylceramides, using Na+, Li+ and K+ as adducting species, showed that the intensity of the fragment ions and the extent of the daughter ion fragmentation of the molecular ions, are dependent on the type of adduct used. The daughter ion spectra of Li+ adduct ions showed intense sequence fragment ions, both of the saccharide chain and the ceramide moiety, and were superior to those obtained using Na+ or K+. The collision-induced dissociation spectra of the [M + Li]+ ions, of glycosphingolipids containing di- to hexasaccharides, are also presented. Proposed possible fragments, resulting from the CID of the molecular ions [M + Li]+ of monoglycosylceramides, are shown.