Gunnel Ahlgren

FATTY ACID CONTENT AND CHEMICAL COMPOSITION OF FRESHWATER MICROALGAE1

Fatty acid (FA), total lipid, protein, amino acid, carbon, nitrogen, and phosphorus content was analyzed in 24 samples of freshwater microalgae. The samples originated from batch, continuous, or mass cultures in various growth phases and from net samples from lakewater. FA were analyzed quantitatively by using an internal standard in a GLC system and expressed as mg·g−1 dry weight (DW). The FA of one group of blue‐greens (e.g. Oscillatoria and Microcystis) were similar to those of the greens with higher amounts of 18C acids of the ω3 type compared to the ω6 type, whereas the other group (e.g. Anabaena and Spirulina) contained mostly ω6 acids. The flagellates, a taxonomically diverse group, were characterized by high amounts of long‐chained (20–22 C) polyunsaturated FA (PUFA), particularly of the ω3 type. The ω3/ω6 ratio appears to be highest in algae in the exponential growth phase. The increased lipid content in stressed algae was mostly due to increased saturated fatty acids and ω6 acids, whereas the valuable ω3 acids were unchanged or even decreased.

Optimum growth conditions and light utilization efficiency of Spirulina platensis (= Arthrospira fusiformis) (Cyanophyta) from Lake Chitu, Ethiopia

Spirulina platensis (= Arthrospira fusiformis) was isolated from Lake Chitu, a saline, alkaline lake in Ethiopia, where it forms an almost unialgal population. Optimum growth conditions were studied in a turbidostat. Cultures grown in modified Zarrouks medium and exposed to a range of light intensities (20–500 µmol photons m−2s−1) showed a maximum specific growth rate (µmax) of 1.78 d−1. Quantum yield for growth (Φµ) was 3.8% at the optimum light for growth of 330 µmol photons m−2s−1, and ranged from 2.8 to 9.4%. With increase in irradiance, the chlorophyll a concentration decreased, and the carotenoids/chlorophyll a ratio increased by a factor of 2.4. The phosphorus to carbon ratio (P/C) showed some variation, while the nitrogen to carbon ratio (N/C) remained relatively constant, thus causing fluctuations in the N:P ratio (7–11) of cells. An optimum N:P ratio of about 7 was attained in cells growing at the optimum light for growth. Results from the continuous culture experiments agreed well with maximum values of photosynthetic efficiency given in the literature for natural populations of S. platensis in the soda lakes of East Africa, Lake Arenguade (Ethiopia), and Lake Simbi (Kenya).

Fatty Acid Ratios in Freshwater Fish, Zooplankton and Zoobenthos – Are There Specific Optima?

Two groups of polyunsaturated fatty acids (PUFA), termed omega-3 and omega-6 in food (or here as n-3 and n-6 PUFA, respectively), are essential for all vertebrates and probably also for nearly all invertebrates. The absolute concentrations of the different PUFA are important, as is an appropriate balance between the two. The optimal ratio of n-3/n-6 is not known for most organisms but is anticipated to be more or less species-specific (Sargent et al. 1995). The three most important PUFA in vertebrates are eicosapentaenoic acid (EPA, 20:5n-3), docosahexaenoic acid (DHA, 22:6n-3) and arachidonic acid (ARA, 20:4n-6). Both EPA and ARA are precursors for biologically active eicosanoids that are vital components of cell membranes and play many dynamic roles in mediating and controlling a wide array of cellular activities (Crawford et al. 1989; Harrison 1990; Henderson et al. 1996; see Chap. 9). Since n-3 and n-6 PUFA cannot be synthesized de novo by most metazoans, they must be included in the diet, either as EPA, DHA and ARA, or as their precursors, such as α-linolenic acid (ALA, 18:3n-3, precursor of EPA and DHA) and linoleic acid (LIN, 18:2n-6, precursor of ARA) (Bell et al. 1986; Sargent et al. 1995). Both ALA and LIN are produced in the thylacoid membranes of algae and plants with chlorophyll (Sargent at al. 1987).

NITROGEN LIMITATION EFFECTS OF DIFFERENT NITROGEN SOURCES ON NUTRITIONAL QUALITY OF TWO FRESHWATER ORGANISMS, SCENEDESMUS QUADRICAUDA (CHLOROPHYCEAE) AND SYNECHOCOCCUS SP. (CYANOPHYCEAE)

Food quality for grazers has been related to mineral (nitrogen, phosphorus) and biochemical (amino acids, fatty acids) constituents. The aim of the study was to examine the influence of different nitrogen sources on these constituents in two organisms, the green alga Scenedesmus quadricauda Turp. and the cyanobacterium Synechococcus sp., commonly used in feeding experiments. The two organisms were grown in continuous cultures at different growth rates. Nitrate or ammonium salts were used as nitrogen sources under both replete and limited conditions. Carbon content (mg·g−1 dry weight) was stable in both organisms independent of nitrogen source, nitrogen limitation, and growth rate. Nitrogen content decreased with limitation and growth rate in Scenedesmus and to a lesser degree in Synechococcus, whereas changes in phosphorus content were not statistically significant. The relative proportions of amino acids (% of total amino acids) were relatively stable in both organisms, whereas the proportions of fatty acids varied with growth rate and limitation. Fatty acid content was much lower in Synechococcus than in Scenedesmus. At N limitation, polyunsaturated fatty acids (PUFAs) showed lower levels in both organisms. The change occurred in the ω3 PUFA (linolenic acid) of the green alga and in the ω6 PUFA (linoleic acid) of the cyanobacterium. The difference in the response of N limitation in the two organisms may be traced to the different composition of the chloroplast membranes (the prokaryotic way) and the microsomal membranes (the eukaryotic way) where the desaturation takes place.

Effects of algal diets and temperature on the growth and fatty acid content of the cichlid fish Oreochromis niloticus L. – A laboratory study

The effects of different algal foods and water temperatures on the growth and fatty acid content of the Nile Tilapia, Oreochromis niloticus L., were studied. Four types of algae, given in the same amounts as the control diet, were used as food: Microcystis aeruginosa, colonial and single-celled forms; Arthrospira fusiformis; and Scenedesmus quadricauda. The control group was fed a commercial diet of cichlid pellets, while another group was left unfed. The feeding experiment was run at 25 °C. The condition factor decreased in all algal fed fish groups, except the one fed on Microcystis colonies, whereas the control group showed no significant change. Both food quantity and quality were responsible for this result. Some short-chained fatty acids in the diets could be traced in the long-chained counter-parts in the fish tissue. Both saturated fatty acids and monounsaturated fatty acids were higher in the control vs. treatment groups, whereas the polyunsaturated fatty acids displayed no significant differences amongst any of the treatment groups studied, including the unfed group. Direct quantitative comparison of individual fatty acid in the diet vs. tissue lipids in the fish proved to be difficult due to the great capacity of these tilapias to elongate and desaturate 18 carbon acids into long-chained homologues. The effect of temperature was studied by growing the fish at 16, 20 and 25 °C. All groups were fed commercial cichlid pellets. The level of saturated and monounsaturated fatty acids increased at 20 °C, whereas polyunsaturated fatty acids showed little variation. Docosahexaenoic acid, belonging to the important ‘omega 3’ group where the first double bond starts at carbon number three, was highest at 16 °C, resulting in a markedly elevated omega-3/omega-6 ratio at that temperature.

Cyanotoxin production in seven Ethiopian Rift Valley lakes

Abstract We hypothesized that unusual deaths and illnesses in wild and domestic animals in lake areas of the Rift Valley south of Addis Ababa were caused by toxic cyanobacteria. In the first cyanotoxic analyses conducted in samples from Ethiopia, we found lakes Chamo, Abaya, Awassa, Chitu, Langano, Ziway, and Koka all had concentrations of microcystins (MC) ranging from trace to hazardous, whereas only traces less than limits of detection (LOD) of cylindrospermopsin (CYN) were found. In the December 2006 dry season we sampled the lakes for analyses of MC, CYN, species structures, and calculations of cyanobacteria biomass. We used the Utermöhl technique to analyse cyanobacterial biomass and monitored MC toxins using HPLC-DAD, LC-ESI-MS-MRM, and ELISA-test and CYN with HPLC-DAD and ELISA. The various toxicity tests coincided well. In 4 of the lakes (Chamo, Langano, Ziway, and Koka), the inter-lake range of total MC concentration was 1.3–48 μg L−1; in 3 (Abaya, Awassa, and Chitu), we found only traces of MC. Microcystis aeruginosawas the dominant species, with Microcystis panniformis, Anabaena spiroides, and Cylindrospermopsisspp. as subdominants. The MC concentration, especially in Lake Koka, exceeded levels for serious health hazards for humans, cattle, and wildlife.

Phosphorus as growth-regulating factor relative to other environmental factors in cultured algae

This review considers how the regulating effect of P on the growth of phytoplankton will be modified by other environmental factors, e.g., the physical factors light and temperature as well as the nutrients N, Si, Se, Fe and C. Questions about interaction effects are considered, as well as the possibility of general description of the interaction phenomena.The general response to nutrient limitation can be considerably altered by light and temperature. The algae use relatively more P with increasing light, and the P content of the algae increases at lower temperature. The algae are, therefore, more sensitive to P limitation at high light and low temperature. The P yield at % MathType!MTEF!2!1!+-% feaafiart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGak0dh9WrFfpC0xh9vqqj-hEeeu0xXdbba9frFj0-OqFf% ea0dXdd9vqaq-JfrVkFHe9pgea0dXdar-Jb9hs0dXdbPYxe9vr0-vr% 0-vqpWqaaeaabiGaciaacaqabeaadaqaaqaaaOqaaiqbeY7aTzaaja% aaaa!3926!\[\hat \mu \] seems to be relatively independent of temperature, but the lower the growth rate, the larger is the influence of the temperature.Two opinions exist of how dual limitation of two nutrients affects the growth rates of phytoplankton: a threshold, non-interactive model where growth is controlled by a single nutrient at a time, and a multiplicative, interactive model where growth is controlled by both suboptimal nutrients simultaneously. Both models are supported by different experimental data.

Phosphorus limitation effects on the fatty acid content and nutritional quality of a green alga and a diatom

Phosphorus limitation effects on the fatty acid content and nutritional quality of a green alga and a diatom

Nutritional quality of Scenedesmus quadricauda (Chlorophyceae) grown in different nitrogen regimes and tested on Daphnia

Nutritional quality of Scenedesmus quadricauda (Chlorophyceae) grown in different nitrogen regimes and tested on Daphnia

Bioaccumulation of microcystins in the food web : a field study of four Swedish lakes

Abstract The transfer of microcystins (MC) up the food chain was measured in 4 lakes in central Sweden; Ekoln, Lilla Ullfjärden, Valloxen, and Storsjön. In lakes Ekoln and Valloxen, Microcystis aeruginosa was the dominant cyanobacterium, while the oscillatorian species Planktothrix prolifica form dense blooms in Lake Lilla Ullfjärden. The cyanobacterial composition in Lake Storsjön was more diverse with several Microcystis and Dolichospermum species. All dominant taxa are well-known producers of hepatotoxic MC. The highest recorded MC in the water samples from Lake Lilla Ullfjärden was measured in the bloom of P. prolifica (35 μg L−1). The highest MC content was measured in invertebrates; however, the MC concentration was usually low in fish. Maximum levels were 9 μg g−1 dry weight (dw) in zooplankton, 10 μg g−1 dw in benthos, and 2.7 μg g−1 dw in fish (smelt) liver. In fish muscle the highest recorded levels were 0.10–0.18 μg g−1 dw in bleak and smelt from Lake Lilla Ullfjärden and in pike-perch and roach from Lake Storsjön. Based on the World Health Organization’s tolerable daily intake value of 0.04 μg kg–1 body weight, we conclude that any risk related to MC from human consumption of fish from these lakes is minimal.