Fatty acid patterns in Chlamydomonas sp. as a marker for nutritional regimes and temperature under extremely acidic conditions

Sequential pressurized liquid extraction to determine brain-originating fatty acids in meat products as markers in bovine spongiform encephalopathy risk assessment studies

A new approach using sequential pressurized liquid extraction described recently [J. Poerschmann, R. Carlson, J. Chromatogr. A, 1127 (2006) 18-25] was applied to determine lipid markers originating from central nervous system (CNS) tissue of cows in heat-processed sausages. These studies are very important in quality control as well as risk assessment studies in the face of the bovine spongiform encephalopathy (BSE) crisis. Diagnostic CNS lipid markers, which should not be present in meat products without CNS addition, were recognized on complete transesterification as polar 2-hydroxy-fatty acids (2OH-24:0, 2OH-24:1, 2OH-22:0, 2OH-18:0, shorthand designation) as well as odd-numbered non-branched fatty acids beyond C(22). An array of other fatty acids including lignoceric acid (24:0), nervonic acid (24:1), arachidonic acid (20:4), and polyunsaturated nC(22)-surrogates are strongly related to CNS lipids, but occur as traces in meat products without CNS addition as well, thus reducing their value as diagnostic markers. Samples including meat products without CNS addition, meat with 3% CNS addition, as well as pure CNS homogenates, were subjected to sequential PLE (pressurized liquid extraction) consisting of two steps: n-hexane/acetone 9:1 (v/v) extraction at 50 degrees C to remove neutral lipids, followed by chloroform/methanol 1:4 (v/v) extraction at 110 degrees C to isolate polar CNS lipids (two 10 min PLE cycles each). To enhance the fractionation efficiency, cyanopropyl modified silica as well as chemically not modified silica sorbent was used at the outlet of the PLE cartridge to retard polar lipids in the first extraction step. This method proved superior to widely distributed exhaustive lipid extraction followed by solid-phase extraction (SPE) using silica regarding lipid recoveries and clear-cut boundaries between lipid classes. Methodological studies showed that the alcoholysis using trimethylchlorosilane/methanol (1:9, v/v) is an excellent method for the complete transesterification of lipids and quantitative formation of methyl esters.

New fractionation scheme for lipid classes based on “in-cell fractionation” using sequential pressurized liquid extraction

A new preparation scheme is proposed to fractionate neutral lipids (acylglycerines, sterol esters, long-chain free fatty acids) from polar phospholipids in biological matrices. This fractionation is mandatory in the microbial community, for the control of bioremediation processes, in the study of phytoplankton growth in lakes and rivers, and in the quality control of processed food. Basically, a two-step pressurized liquid extraction (PLE) scheme is combined with an "in-cell-fractionation" using silica-based sorbents placed at the outlet of the PLE cartridge. The optimized extraction scheme consists of n-hexane/acetone (9:1, v/v) extraction at 50 degrees C (2 cycles, 10 min each) to obtain neutral lipids followed by chloroform/methanol (1:4, v/v) extraction at 110 degrees C (2 cycles, 10 min each). Thermally pre-treated silicic acid and cyanoproyl-modified silica turned out to be appropriate sorbents to ensure clear-cut boundaries between neutral lipids and phospholipids. The proposed protocol is superior to commonly used approaches consisting of an exhaustive lipid extraction followed by off-line lipid fractionation using solid-phase extraction (SPE) regarding fractionation efficiency, time and solvent consumption. In this paper, it is also shown that the transmethylation using trimethylchlorosilane/methanol (1:9, v/v) provides a complete reaction to give methyl esters without artefact formation across the array of different lipid classes even with polyunsaturated fatty acid moieties.

Lipids and lipid metabolism in eukaryotic algae

Eukaryotic algae are a very diverse group of organisms which inhabit a huge range of ecosystems from the Antarctic to deserts. They account for over half the primary productivity at the base of the food chain. In recent years studies on the lipid biochemistry of algae has shifted from experiments with a few model organisms to encompass a much larger number of, often unusual, algae. This has led to the discovery of new compounds, including major membrane components, as well as the elucidation of lipid signalling pathways. A major drive in recent research have been attempts to discover genes that code for expression of the various proteins involved in the production of very long-chain polyunsaturated fatty acids such as arachidonic, eicosapentaenoic and docosahexaenoic acids. Such work is described here together with information about how environmental factors, such as light, temperature or minerals, can change algal lipid metabolism and how adaptation may take place.

High heterotrophic bacterial production in acidic, iron-rich mining lakes

The acidic mining lakes of Eastern Germany are characterized by their extremely low pH and high iron concentrations. Low concentrations of CO2 in the epilimnion due to the low pH and reduced light transmission due to dissolved ferric iron potentially limit phytoplankton primary production (PP), whereas dissolved organic carbon (DOC) may promote heterotrophic production of bacteria (HP). We, therefore, tested whether HP exceeds PP in three lakes differing in pH and iron concentration (mean pH 2.3-3.0, 23-500 mg Fe L(-1)). Bacterial biomass and HP achieved highest values in the most acidic, most iron-rich lake, whereas PP was highest in the least acidic lake. HP was often higher than PP (ratio HP/PP up to 11), indicating that planktonic PP was not the main carbon source for the bacteria. HP was not related to PP and DOC, but HP as well as bacterial biomass increased with decreasing pH. Light stimulated the formation of ferrous iron, changed the DOC composition, and increased the HP in laboratory experiments, suggesting that iron photoreduction caused DOC degradation. This may explain why we found the highest HP in the most acidic and most rich lake. Overall, the importance of bacteria in the cycling of matter and as a basis for the whole food web seemed to increase in more acidic lakes with higher iron concentrations.