Transfection efficiency and cytotoxicity of cationic liposomes in primary cultures of rainbow trout (Oncorhynchus mykiss) gill cells

Immunisation of fish by immersion has been applied for inactivated, whole cell bacterins, where the gill epithelial cells are considered as one of the prime uptake sites. Antigen entry is a critical factor for delivery of vaccine antigens through the immersion route, also for DNA vaccines, and delivery systems like cationic liposomes may enhance uptake. In this study, the aim was to examine the efficiency of cationic liposomes as a means to transfect primary cultures of rainbow trout gill cells with plasmids encoding viral or reporter proteins. Furthermore, the effects of the concentration and composition of liposomes/lipoplex on the viability of the cells were evaluated. Transfection of the gill cells was possible with both plasmids following transfection with lipoplexes of a neutral charge. Low concentrations and neutral/negatively charged formulations were favourable with respect to the toxicity of the formulations. Given that the mucous barrier covering the gills is overcome, this system might be useful for the priming of the local immunity in the fish gills.     

Liver and muscle fatty acid composition of mature and immature rainbow trout (<Emphasis Type="Italic">Oncorhynchus mykiss</Emphasis>) fed two different diets

Fatty acid composition of liver and muscle tissues of immature and mature Oncorhynchus mykiss fed on two different diets were determined. Fatty acid analyses were carried out by gas chromatography. Palmitic acid (C16:0), oleic acid (C18:1 n-9), linoleic acid (C18:2 n-6) and docosahexaenoic acid (C22:6 n-3) were the major components in both liver and muscle tissues of immature and mature rainbow trout of both sexes. The amounts of C22:6 n-3 were higher in the liver (29.04 ± 0.06 − 27.41 ± 0.17%) and muscle (13.05 ± 0.40 − 11.37 ± 0.21%) of immature fish than in mature fish and depended on the composition of the diet. Results of this study show that fatty acid composition in fish tissues can considerably vary, depending on the age of fish and their diet. Thus more detailed studies are necessary on the influence of diet on immature and mature fish fatty acid composition. The age and diet of fish consumed may also be important for human health.     

Effects of global change factors on fatty acids and mycosporine‐like amino acid production in Chroothece richteriana (Rhodophyta)

Under natural conditions, Chroothece richteriana synthesizes a fairly high proportion of fatty acids. However, nothing is known about how environmental changes affect their production, or about the production of protective compounds, when colonies develop under full sunshine with high levels of UV radiation. In this study, wild colonies of C. richteriana were subjected to increasing temperature, conductivity, ammonium concentrations and photosynthetically active radiation (PAR), and UV radiations to assess the potential changes in lipid composition and mycosporine‐like amino acids (MAAs) concentration. The PERMANOVA analysis detected no differences for the whole fatty acid profile among treatments, but the percentages of α‐linolenic acid and total polyunsaturated fatty acids increased at the lowest assayed temperature. The percentages of linoleic and α‐linolenic acids increased with lowering temperature. γ‐linolenic and arachidonic acids decreased with increasing conductivity, and a high arachidonic acid concentration was related with increased conductivity. The samples exposed to UVB radiation showed higher percentages of eicosapentaenoic acid and total monounsaturated fatty acids, at the expense of saturated fatty acids. MAAs accumulation increased but not significantly at the lowest conductivity, and also with the highest PAR and UVR exposure, while ammonium and temperature had no effect. The observed changes are probably related with adaptations of both membrane fluidity to low temperature, and metabolism to protect cells against UV radiation damage. The results suggest the potential to change lipid composition and MAAs concentration in response to environmental stressful conditions due to climate change, and highlight the interest of the species in future research about the biotechnological production of both compound types.     

Ichthyotoxicity of Chattonella marina (Raphidophyceae) to damselfish (Acanthochromis polycanthus): the synergistic role of reactive oxygen species and free fatty acids

This investigation aimed to elucidate the relative roles of putative brevetoxins, reactive oxygen species and free fatty acids as the toxic principle of the raphidophyte Chattonella marina, using damselfish as the bioassay. Our investigations on Australian C. marina demonstrated an absence or only very low concentrations of brevetoxin-like compounds by radio-receptor binding assay and liquid chromatography–mass spectroscopy techniques. Chattonella is unique in its ability to produce levels of reactive oxygen species 100 times higher than most other algal species. However, high levels of superoxide on their own were found not to cause fish mortalities. Lipid analysis revealed this raphidophyte to contain high concentrations of the polyunsaturated fatty acid eicosapentaenoic acid (EPA; 18–23% of fatty acids), which has demonstrated toxic properties to marine organisms. Using damselfish as a model organism, we demonstrated that the free fatty acid (FFA) form of EPA produced a mortality and fish behavioural response similar to fish exposed to C. marina cells. This effect was not apparent when fish were exposed to other lipid fractions including a triglyceride containing fish oil, docosahexaenoate-enriched ethyl ester, or pure brevetoxin standards. The presence of superoxide together with low concentrations of EPA accelerated fish mortality rate threefold. We conclude that the enhancement of ichthyotoxicity of EPA in the presence of superoxide can account for the high C. marina fish killing potential.     

Antioxidant defense of rainbow trout (Oncorhynchus mykiss) in relation to dietary n-3 highly unsaturated fatty acids and vitamin E contents

This study examined the modulation of the antioxidant status and related physiological changes in rainbow trout Oncorhynchus mykiss under different levels of dietary n-3 highly unsaturated fatty acids (n-3 HUFA) and vitamin E. Six diets containing 0, 100 or 1000 mg alpha-tocopheryl acetate kg(-1) diet and 20% or 48% n-3 HUFA provided by normal fish oil or DHA concentrated fish oil, respectively, were fed to 100 g size fish for 15 weeks. Growth of fish fed vitamin E deficient diets under both levels of n-3 HUFA were slightly retarded, accompanied by a reduction of hematocrit values, an enlargement of liver and spleen, an elevation of lipid hydroperoxide in red blood cell and the antioxidant enzymes (superoxide dismutase, catalase, glutathione peroxidase). Supplementation of vitamin E could protect the fish from these adverse effects; however the higher dose was no better compared to the moderate dose. The modulations were clearly seen in fish fed high n-3 HUFA (48%) since they were under greater oxidative stress as indicated by the markers, lipid hydroperoxide and 8-isoprostane. The increased activity of enzymes corresponds to physiological mechanisms combating the elevation of free radicals under oxidative stress and a dietary fatty acid profile-dependent moderate dose of vitamin E is all that is required to function as an effective antioxidant.     

Fatty acids and stable isotopes (δ13C and δ15N) reveal temporal changes in narwhal (Monodon monoceros) diet linked to migration patterns

Narwhals (Monodon monoceros) are sentinel species in the Arctic and to investigate marine food web changes from 1982–2011 we examined diet using fatty acids, δ¹⁵N, and δ¹³C, in narwhals from Baffin Bay (BB) and northern Hudson Bay (NHB). We predicted temporal changes would be greater in NHB due to a significant reduction in summer ice cover. In NHB, δ¹⁵N significantly increased, δ¹³C displayed a parabolic trend, and fatty acids gradually shifted, albeit not significantly, over time. δ¹⁵N was stable, δ¹³C decreased, and fatty acids significantly changed over time in BB. Stable isotope mixing models indicated a dietary reduction in capelin and increase in Greenland halibut from 1994–2000 to 2006–2011 in BB, while capelin was an important dietary component for narwhals in NHB in recent years (2006–2011). These dietary changes may be attributed to changes in sea ice and narwhal migration. Seasonal dietary changes, as evidenced by changes in blubber fatty acids and skin and muscle stable isotopes, were not as apparent in the NHB population, which may be indicative of a reduced migratory distance. Long‐term monitoring of narwhal diet and migratory patterns associated with reduced sea ice provides invaluable information about how the marine ecosystem will redistribute with global warming.     

Adjustments in fatty acid composition is a mechanism that can explain resilience to marine heatwaves and future ocean conditions in the habitat‐forming seaweed Phyllospora comosa (Labillardière) C.Agardh

Marine heatwaves are extreme events that can have profound and lasting impacts on marine species. Field observations have shown seaweeds to be highly susceptible to marine heatwaves, but the physiological drivers of this susceptibility are poorly understood. Furthermore, the effects of marine heatwaves in conjunction with ocean warming and acidification are yet to be investigated. To address this knowledge gap, we conducted a laboratory culture experiment in which we tested the growth and physiological responses of Phyllospora comosa juveniles from the southern extent of its range (43–31°S) to marine heatwaves, ocean warming and acidification. We used a ‘collapsed factorial design’ in which marine heatwaves were superimposed on current (today's pH and temperature) and future (pH and temperature projected by 2100) ocean conditions. Responses were tested both during the heatwaves, and after a 7‐day recovery period. Heatwaves reduced net photosynthetic rates in both current and future conditions, while respiration rates were elevated under heatwaves in the current conditions only. Following the recovery period, there was little evidence of heatwaves having lasting negative effects on growth, photosynthesis or respiration. Exposure to heatwaves, future ocean conditions or both caused an increase in the degree of saturation of fatty acids. This adjustment may have counteracted negative effects of elevated temperatures by decreasing membrane fluidity, which increases at higher temperatures. Furthermore, P. comosa appeared to down‐regulate the energetically expensive carbon dioxide concentrating mechanism in the future conditions with a reduction in δ¹³C values detected in these treatments. Any saved energy arising from this down‐regulation was not invested in growth and was likely invested in the adjustment of fatty acid composition. This adjustment is a mechanism by which P. comosa and other seaweeds may tolerate the negative effects of ocean warming and marine heatwaves through benefits arising from ocean acidification.     

Changes in fatty acid composition and degree of unsaturation of (brady)rhizobia as a response to phases of growth, reduced water activities and mild desiccation

The effects of growth phase, reductions in the water activity (a _w) of the growth medium and mild desiccation on the composition and the degree of unsaturation of cellular fatty acids (CFA) of Sinorhizobium meliloti, Bradyrhizobium elkaniiand Bradyrhizobium japonicum were studied. During the course of growth, an interchange of cis-vaccenic with lactobacillic acid and a slight increase in palmitic acid were observed while other fatty acids remained constant. The degree of unsaturation was significantly higher in the exponential phase of growth. Reductions in the a _w of the medium led to an increase in lag phase, a reduction in growth rate and maximal optical densities (OD) in stationary phase cells. A decrease in the degree of unsaturation of CFA was also observed as the a _w was reduced from 0.999 to 0.969 and after desiccation to 83.5% relative humidity (R.H.). The changes in the degree of unsaturation of CFA observed after growth at reduced a _w may be one of the pre-adaptation steps to endure more severe desiccation.     

The effect of nitrogen limitation on acetyl-CoA carboxylase expression and fatty acid content in Chromera velia and Isochrysis aff. galbana (TISO)

Lipids from microalgae have become a valuable product with applications ranging from biofuels to human nutrition. While changes in fatty acid (FA) content and composition under nitrogen limitation are well documented, the involved molecular mechanisms are poorly understood. Acetyl-CoA carboxylase (ACCase) is a key enzyme in the FA synthesis and elongation pathway. Plastidial and cytosolic ACCases provide malonyl-CoA for de novo FA synthesis in the plastid and FA elongation in the endoplasmic reticulum, respectively. The present study aimed at investigating the expression of plastidial and cytosolic ACCase in Chromera velia and Isochrysis aff. galbana (TISO) and their impact on FA content and elongation level when grown under nitrogen-deplete conditions. In C. velia, plastidial ACCase was significantly upregulated during nitrogen starvation and with culture age, strongly correlating with increased FA content. Conversely, plastidial ACCase of I. aff. galbana was not differentially expressed in nitrogen-deplete cultures, but upregulated during the logarithmic phase of nitrogen-replete cultures. In contrast to plastidial ACCase, the cytosolic ACCase of C. velia was downregulated with culture age and nitrogen-starvation, strongly correlating with an increase in medium-chain FAs. In conclusion, the expression of plastidial and cytosolic ACCase changed with growth phase and nutrient status in a species-specific manner and nitrogen limitation did not always result in FA accumulation.