Light-induced changes in fatty acid profiles of specific lipid classes in several freshwater phytoplankton species

We tested the influence of two light intensities [40 and 300 µmol PAR / (m² s)] on the fatty acid composition of three distinct lipid classes in four freshwater phytoplankton species. We chose species of different taxonomic classes in order to detect potentially similar reaction characteristics that might also be present in natural phytoplankton communities. From samples of the bacillariophyte Asterionella formosa, the chrysophyte Chromulina sp., the cryptophyte Cryptomonas ovata and the zygnematophyte Cosmarium botrytis we first separated glycolipids (monogalactosyldiacylglycerol, digalactosyldiacylglycerol, and sulfoquinovosyldiacylglycerol), phospholipids (phosphatidylcholine, phosphatidylethanol-amine, phosphatidylglycerol, phosphatidylinositol, and phosphatidylserine) as well as non-polar lipids (triacylglycerols), before analyzing the fatty acid composition of each lipid class. High variation in the fatty acid composition existed among different species. Individual fatty acid compositions differed in their reaction to changing light intensities in the four species. Although no generalizations could be made for species across taxonomic classes, individual species showed clear but small responses in their ecologically-relevant omega-3 and omega-6 polyunsaturated fatty acids in terms of proportions and of per carbon quotas. Knowledge on how lipids like fatty acids change with environmental or culture conditions is of great interest in ecological food web studies, aquaculture and biotechnology, since algal lipids are the most important sources of omega-3 long-chain polyunsaturated fatty acids for aquatic and terrestrial consumers, including human

Simultaneous Effects of Light Intensity and Phosphorus Supply on the Sterol Content of Phytoplankton

Sterol profiles of microalgae and their change with environmental conditions are of great interest in ecological food web research and taxonomic studies alike. Here, we investigated effects of light intensity and phosphorus supply on the sterol content of phytoplankton and assessed potential interactive effects of these important environmental factors on the sterol composition of algae. We identified sterol contents of four common phytoplankton genera, Scenedesmus, Chlamydomonas, Cryptomonas and Cyclotella, and analysed the change in sterol content with varying light intensities in both a high-phosphorus and a low-phosphorus approach. Sterol contents increased significantly with increasing light in three out of four species. Phosphorus-limitation reversed the change of sterol content with light intensity, i.e., sterol content decreased with increasing light at low phosphorus supply. Generally sterol contents were lower in low-phosphorus cultures. In conclusion, both light and phosphorus conditions strongly affect the sterol composition of algae and hence should be considered in ecological and taxonomic studies investigating the biochemical composition of algae. Data suggest a possible sterol limitation of growth and reproduction of herbivorous crustacean zooplankton during summer when high light intensities and low phosphorus supply decrease sterol contents of algae

Phytoplankton sterol contents vary with temperature, phosphorus and silicate supply : a study on three freshwater species

The understanding of environmentally induced changes in the biochemical composition of phytoplankton species is of great importance in both physiological studies and ecological food web research. In extensive laboratory experiments we tested the influence of two different temperatures (10 C and 25 C) and a phosphorus supply gradient on the sterol concentrations of the three freshwater phytoplankton species Scenedesmus quadricauda, Cryptomonas ovata and Cyclotella meneghiniana.The diatom C. meneghiniana was additionally exposed to a silicate gradient. In two separate experiments we analysed (1) possible interactive effects of temperature and phosphorus supply and (2) the effect of four phosphorus levels and three silicate levels on algal sterol concentrations. We observed that sterol concentrations were higher at 25 C than at 10 C in S. quadricauda and C. meneghiniana, but were not affected by temperature in C. ovata. Interactive effects of temperature and phosphorus supply on sterol concentrations were found in C. meneghiniana. This presumably was due to the bioconversion ofone sterol (24-methylenecholesterol) into another (22-dihydrobrassicasterol). Increasing phosphorus supply resulted in species-specific effects on sterol concentrations, viz. an optimum curve response in S. quadricauda, a saturation curve response in C. meneghiniana and no change in sterol concentration in C. ovata. Effects of silicate supply on the sterols of C. meneghiniana equalled the effects of phosphorus supply. Albeit we did not observe a general trend in the three phytoplankton species tested, we conclude that sterol concentrations of phytoplankton are strongly affected by temperature and nutrient supply. Interactive effects point out the importance of taking into account more than just one environmental factorwhen assessing the effects of environmentally induced changes on phytoplankton sterol concentrations

Photosynthetic and fatty acid acclimation of four phytoplankton species in response to light intensity and phosphorus availability

<div><p>Photosynthetic acclimation of phytoplankton to lower irradiation can be met by several strategies such as increasing the affinity for light or increasing antenna size and stacking of the thylakoids. The latter is reflected by a higher proportion of polyunsaturated fatty acids (PUFAs). Additionally, photosynthetic capacity (P_max), respiratory losses, and proton leakage can be reduced under low light. Here we consider the effect of light intensity and phosphorus availability simultaneously on the photosynthetic acclimation and fatty acid composition of four phytoplankters. We studied representatives of the Chlorophyceae, Cryptophyceae and Mediophyceae, all of which are important components of plankton communities in temperate lakes. In our analysis, excluding fatty acid composition, we found different acclimation strategies in the chlorophytes <i>Scenedesmus quadricauda, Chlamydomonas globosa</i>, cryptophyte <i>Cryptomonas ovata</i> and ochrophyte <i>Cyclotella meneghiniana</i>. We observed interactive effects of light and phosphorus conditions on photosynthetic capacity in <i>S. quadricauda</i> and <i>Cry. ovata. Cry. ovata</i> can be characterized as a low light-acclimated species, whereas <i>S. quadricauda</i> and <i>Cyc. meneghiniana</i> can cope best with a combination of high light intensities and low phosphorus supply. Principal component analyses (PCA), including fatty acid composition, showed further species-specific patterns in their regulation of P_max with PUFAs and light. In <i>S. quadricauda</i> and <i>Cyc. meneghiniana</i>, PUFAs negatively affected the relationship between P_max and light. In <i>Chl. globosa</i>, lower light coincided with higher PUFAs and lower P_max, but PCA also indicated that PUFAs had no direct influence on P_max. PUFAs and P_max were unaffected by light in <i>Cry. ovata</i>. We did not observe a general trend in the four species tested and concluded that, in particular, the interactive effects highlight the importance of taking into account more than one environmental factor when assessing photosynthetic acclimation to lower irradiation.</p></div

Change in sterol content with light intensity in <i>Scenedesmus quadricauda</i>.

<p>(▴, straight line) High-P treatments. (○, dashed line) Low-P treatments. Each data point represents a single culture. Superscripts indicate statistically significant effects of light intensity (l), phosphorus supply (P), or interaction of these two factors (l*P). A regression line was added if one of the effects was significant.</p

P-values of ANCOVA for changes in sterol contents of four phytoplankton species, depending on the continuous variable light intensity (l, log_e-transformed) and the factor medium phosphorus concentration (P).

<p>P-values of ANCOVA for changes in sterol contents of four phytoplankton species, depending on the continuous variable light intensity (l, log_e-transformed) and the factor medium phosphorus concentration (P).</p

Change in sterol content with light intensity in <i>Cyclotella meneghiniana</i>.

<p>(▴, straight line) High-P treatments. (○, dashed line) Low-P treatments. Superscripts indicate statistically significant effects of light intensity (l), phosphorus supply (P), or interaction of these two factors (l*P). A regression line was added if one of the effects was significant.</p

Change in sterol content with light intensity in <i>Chlamydomonas globosa.</i>

<p>(▴, straight line) High-P treatments. (○, dashed line) Low-P treatments. Superscripts indicate statistically significant effects of light intensity (l), phosphorus supply (P), or interaction of these two factors (l*P). A regression line was added if one of the effects was significant.</p