The membrane lipids of the marine ciliated protozoan Parauronema acutum

Fatty Acids of Marine Mollusks: Impact of Diet, Bacterial Symbiosis and Biosynthetic Potential

The n-3 and n-6 polyunsaturated fatty acid (PUFA) families are essential for important physiological processes. Their major source are marine ecosystems. The fatty acids (FAs) from phytoplankton, which are the primary producer of organic matter and PUFAs, are transferred into consumers via food webs. Mollusk FAs have attracted the attention of researchers that has been driven by their critical roles in aquatic ecology and their importance as sources of essential PUFAs. The main objective of this review is to focus on the most important factors and causes determining the biodiversity of the mollusk FAs, with an emphasis on the key relationship of these FAs with the food spectrum and trophic preference. The marker FAs of trophic sources are also of particular interest. The discovery of new symbioses involving invertebrates and bacteria, which are responsible for nutrition of the host, deserves special attention. The present paper also highlights recent research into the molecular and biochemical mechanisms of PUFA biosynthesis in marine mollusks. The biosynthetic capacities of marine mollusks require a well-grounded evaluation.

Ciliate (Euplotes sp.) predation by Pseudodiaptomus annandalei (Copepoda: Calanoida) and the effects of mono-algal and pluri-algal diets

Background

Pseudodiaptomus annandalei is an estuarine species and being cultured as live feed for grouper fish larvae and other planktivores. We examined the predation behavior of P. annandalei adults when preying on ciliated protists (Euplotes sp.) and the effects of mono- and pluri-algal diets on ciliate predation by P. annandalei under laboratory conditions. The algal food comprised the pigmented flagellate Isochrysis galbana (4 ~ 5 μm) and Tetraselmis chui (17 ~ 20 μm).

Results

Males and females of P. annandalei consumed 8 ~ 15 ciliate cells/h. The probability of ciliate ingestion following an attack was a direct function of the copepod's hunger level. Conversely, the probability of prey rejection after capture was a negative function of the copepod's hunger level. Starved and poorly fed females showed a significantly lower rate of prey rejection compared to similarly treated males. The duration of handling a ciliate prey did not significantly differ between males and females of P. annandalei. Starved copepods spent less time handling a ciliate prey than fed copepods. Prey ingestion rates showed a negative relation with the feeding duration, whereas the prey rejection rate increased as the feeding duration increased. The ciliate consumption rate of P. annandalei was significantly lower in the presence of mixed algae. Neither I. galbana nor T. chui alone had any significant effect on ciliate consumption by P. annandalei.

Conclusions

The results confirmed that P. annandalei ingests bacterivorous heterotrophic protists even in the presence of autotrophic protists. Therefore, our results point to the role of P. annandalei in the transfer of microbial carbon to the classical food chain in estuarine and brackish water ecosystems.

Cryptophyceae and rhodophyceae; chemotaxonomy, phylogeny, and application

The biochemical compositions of seven strains of marine cryptomonad and a rhodophyte were determined in logarithmic phase batch (1.4 L flask) and semi-continuous (10 L carboy) culture. Lipid ranged from 13% to 28%, protein ranged from 53% to 68%, and carbohydrate ranged from 9% to 24% of the organic weight. The major lipid classes in the species examined were polar lipids (78-88% of total lipid). The major sterol in the Cryptophyceae and the Rhodophyceae was 24-methylcholesta-5,22E-dien-3beta-ol (62-99% of total sterols); which is also the major sterol in some diatoms and haptophytes. Smaller proportions of cholest-5-en-3beta-ol (1-17.7%) were also found in the Cryptophyceae. Most cryptomonads contained high proportions of the n-3 polyunsaturated fatty acids (PUFA), 18:3n-3 (20.7-29.9% of the total fatty acids), 18:4n-3 (12.5-30.2%), 20:5n-3 (7.6-13.2%) and 22:6n-3 (6.4-10.8%). However, the blue-green cryptomonad Chroomonas placoidea was characterized by a low proportion of 22:6n-3 (0.2% of total fatty acids), and a significant proportion of 22:5n-6 (4.5%), and the presence of 24-ethylcholesta-5,22E-dien-3beta-ol (35.5% of total sterols). The fatty acid composition of the rhodophyte Rhodosorus sp. was similar to those of the Cryptophyceae except for lower proportions of 18:4n-3 and lack of C21 and C22 PUFA. It is postulated that the primary endosymbiosis of a photosynthetic n-3 C18 PUFA-producing prokaryote and a eukaryotic host capable of chain elongation and desaturation of exogenous PUFA, resulted in the Rhodophyceae capable of producing n-3 C20 PUFA. The secondary endosymbiosis of a photosynthetic n-3 C20 PUFA-producing eukaryote (such as a Rhodosorus sp. like-rhodophyte) and a eukaryotic host capable of further chain elongation and desaturation, resulted in the Cryptophyceae being capable of producing n-3 C20 and C22 PUFA de novo. Selected isolates were examined further in feeding trials with juvenile Pacific oysters (Crassostrea gigas). Rhodomonas salina CS-24(containing elevated 22:6n-3) produced high growth rates in oysters; equivalent to the microalga commonly used in aquaculture, Isochrysis sp. (T.ISO).

Uptake and rapid transfer of fluorescent ceramide analogues to acidosomes (late endosomes) in Paramecium

The ciliated protozoan Paramecium incorporates sphingolipids into its cell membranes. However, it is still unclear if these sphingolipids are metabolically synthesized in the cell or if their precursors are taken up from exogenous materials. Here we studied the route of uptake of fluorescence-labeled analogues of ceramide. Fluorescent ceramide was taken up rapidly independent of phagosome formation. Cold treatment caused a decrease in uptake, while reduction in the amount of cytosolic ATP induced by NaN(3) and deoxyglucose resulted in accumulation without internalization of fluorescence at the plasma membrane. These results suggest that uptake of fluorescent ceramide occurs at the plasma membrane, that it is an ATP-dependent process, and that it is not a result of simple diffusion. At first intracellular fluorescence appeared principally in the posterior half of the cell and then spread throughout the cytosol. In particular, a high accumulation of fluorescence occurred in association with acidosomes (late endosome or multivesicular body-like vesicles) that bind to the surface of nascent and young phagosomes. Therefore, in the Paramecium cell a significant proportion of ceramide apparently enters the cell by endocytosis and is quickly relayed to acidosomes along the endocytic pathway before becoming part of the digestive vacuole (phagoacidosome) membrane.

Assimilation of toluene carbon along a bacteria-protist food chain determined by 13C-enrichment of biomarker fatty acids

A food chain consisting of toluene, toluene-degrading Pseudomonas sp. PS+ and a bacterivorous flagellated amoebae Vahlkampfia sp. was established in a batch culture. This culture was amended with [U-13C]toluene and served as a model system to elucidate the flux of carbon in the food chain by quantifying bacterial biovolumes and 13C enrichment of phospholipid fatty acid (PLFA) biomarkers of the bacteria and the heterotrophic protists. Major PLFA detected in the batch co-culture included those derived from Pseudomonas sp. PS+ (16:1omega7c and 18:1omega7c) and Vahlkampfia sp. (20:4omega6c and 20:3omega6c). A numerical model including consumption of toluene by the bacteria and predation of the bacteria by the heterotrophic protists was adjusted to the measured toluene carbon, bacterial carbon and delta13C values of bacterial and protist biomass. Using this model, we estimated that 28+/-7% of the consumed toluene carbon was transformed into bacterial biomass, and 12+/-4% of the predated bacterial carbon was incorporated into heterotrophic protist biomass. Our study showed that the 13C enrichment of PLFA biomarkers coupled to biomass determination via biovolume calculations is a suitable method to trace carbon fluxes in protist-inclusive microbial food chains because it does not require the separation of protist cells from bacterial cells and soil particles.

Molecular characterization of a highly heterogeneous mixture of glucosylceramides from a deep-water Mediterranean scleractinian coral Dendrophyllia cornigera

We report here on the structural characterization of a highly heterogeneous mixture of glucosylceramides (GlcCers) isolated from a deep-water Mediterranian dendrophylliid coral, Dendrophyllia cornigera. The neutral glycosphingolipid (GSL) components of the coral were separated into three HPLC fractions which were structurally characterized by nuclear magnetic resonance (NMR) and mass spectrometry (MS). NMR analysis revealed a beta-glucosylpyranose, a methyl branched conjugated sphingadienine and alpha-hydroxy fatty acid moieties characteristic for the species. Molecular mass distributions of the HPLC fractions were monitored using single-stage MS. At least 17 different GlcCer constituents with variable long-chain base and fatty acid residues were observed based on the molecular ion peaks in the liquid secondary ion (LSI) survey spectra. Structures of the individual components were revealed by product ion spectra of the alkali-cationized molecules ([M + Cat](+)), which resulted in two characteristic fragment ions, F(F) and F(S). Tandem MS of the same fragment ions formed in the ion source showed that F(F) carries the hydoxy fatty acid, while F(S) carries the long-chain sphingoid base, thus providing complementary structural information for the characterization of ceramide composition. Based on the tandem mass spectra of the molecular ions [M + Na](+), 26 different GlcCers of the coral were identified. The ceramide moiety showed heterogeneity in both the sphingoid portion (d18:2, d19:2, d20:2 and d20:3) and the alpha-hydroxy fatty acid chain (h19-h24, either saturated or unsaturated), forming an extremely heterogeneous mixture. The method is generally applicable to the characterization of structurally heterogeneous GlcCer mixtures.