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Changes in the molar percentage of two omega-3 fatty acids, 20:5n-3 (EPA) and 22:6n-3 (DHA), occur in juvenile northern quahogs, Mercenaria mercenaria, as descending autumn temperatures approach winter lows in the temperate zone. Incorporation of these highly unsaturated fatty acids compensates for the effect of low temperature on cell membrane viscosity by lowering the phase transition of membrane phospholipids. Prior studies have demonstrated that the ability of bivalve mollusks, like M. mercenaria, to manufacture these compounds de novo does not exist or may be limited at best. Insufficient exogenous supply of EPA and DHA, therefore, may restrict their ability to overcome the inhibiting effect of high viscosity on cell membrane phospholipids during this interval. In the present study, a matrix of cultured algae containing various quantities of these compounds was administered to four groups of juvenile M. mercenaria as they adapted to low temperature. Each group displayed a unique response to diet in relative fatty acid profile and mortality. The group receiving abundant EPA adapted well during the early-phase temperature decline, and the one receiving abundant DHA adapted well to the late-phase temperature decline. The group receiving abundant DHA also enjoyed best overall survival following a severe 5-day drop in temperature. The strain native to the local region suffered between 31 and 117 % higher mortality than the notata strain during the 72-day period of temperature decline from 18 to 6 °C. [ABSTRACT FROM AUTHOR]

Senegalese sole ( Solea senegalensis) is a eurytherm teleost that under natural conditions can be exposed to annual water temperature fluctuations between 12 and 26°C. This study assessed the effects of temperature on sole metabolic status, in particular in what concerns plasma free amino acid changes during thermal acclimation. Senegalese sole maintained at 18°C were acclimated to either cold (12°C) or warm (26°C) environmental temperatures for 21 days. Fish maintained at 18°C served as control. Plasma concentrations of cortisol, glucose, lactate, triglycerides, proteins, and free amino acids were assessed. Cold acclimation influenced interrenal responses of sole by increasing cortisol release. Moreover, plasma glucose and lactate concentrations increased linearly with temperature, presumably reflecting a higher metabolic activity of sole acclimated to 26°C. Acclimation temperature affected more drastically plasma concentrations of dispensable than that of indispensable amino acids, and different acclimation temperatures induced different responses. Asparagine, glutamine and ornithine seem to be of particular importance for ammonia detoxification mechanisms, synthesis of triglycerides that may be used during homeoviscous adaptation and, to a lesser extent, as energetic substrates in specimens acclimated to 12°C. When sole is acclimated to 26°C taurine, glutamate, GABA and glycine increased, which may suggest important roles as antioxidant defences, in osmoregulatory processes and/or for energetic purposes at this thermal regimen. In conclusion, acclimation to different environmental temperatures induces several metabolic changes in Senegalese sole, suggesting that amino acids may be important for thermal acclimation. [ABSTRACT FROM AUTHOR]

In this study, we examine changes in fatty acid composition of polar and neutral lipids in gill, liver, and muscle of freshwater alewives ( Alosa pseudoharengus) after temperature challenges in the laboratory. Alewives experienced either a warm or cold challenge in which temperatures were raised or lowered 0.5°C day over 4-6 weeks. In alewives experiencing the cold challenge, gill polar lipids showed evidence of significant remodeling, including decreases in palmitic acid and saturated fatty acids and increases in n-3 and n-6 highly unsaturated fatty acids including docosahexaenoic acid (DHA) and arachidonic acid. In alewives experiencing the warm challenge, we observed significant increases in saturated fatty acids (due mainly to increased palmitic acid) and decreases in polyunsaturated fatty acids in polar lipids of muscle and liver tissue. Fish that died during the cold challenge had significantly higher levels of palmitic acid in muscle polar lipids compared to fish that survived; fish that died during the warm challenge displayed complex changes in fatty acid composition. Based on theoretical considerations, the changes in polar lipids we observed during thermal acclimation are likely to promote appropriate membrane fluidity under each thermal regime. The increased incorporation of highly unsaturated fatty acids during cold acclimation could have significant physiological and ecological implications. In particular, since highly unsaturated fatty acids are typically scarce in freshwater food webs, dietary deficiencies in these essential fatty acids may be a significant factor in winter mortality of freshwater alewives. [ABSTRACT FROM AUTHOR]

Bacillus sp. ORAs2 and Pseudomonas sp. ORAs5, two arsenic-resistant bacterial strains previously isolated from sediments of the Orbetello Lagoon, Italy, were tested for their adaptation to mixed contaminants on the level of membrane fatty acid composition. The two bacterial strains were characterized by high levels of arsenic resistance, and Pseudomonas sp. ORAs5 was also shown to be solvent-tolerant. The bacterial strains were exposed to mixtures of two toxic compounds: arsenic at fixed concentrations and toluene in variable amounts or, alternatively, toluene at constant values along with arsenic added at variable concentrations. Both strains react to the contaminants by changing the composition of their membrane fatty acids. Bacillus sp. strain ORAs2 showed a correlation between growth rate decreases and fatty acids degree of saturation increases in both cases, although pointedly in the presence of 1, 2, and 3 mM of toluene and different additions of arsenic, counteracting membranes fluidity induced by toxic compounds. In Pseudomonas sp. ORAs5, adaptive changes in membrane composition was observed both in terms of increases in the degree of saturation and in the trans/ cis ratio of unsaturated fatty acids in the presence of varying toluene and constant arsenic concentrations, whereas only minor changes occurred with increasing arsenic and constant toluene concentrations. Thus, on the level of membrane composition, Bacillus sp. ORAs2 showed a higher potential for adaptation to the presence of mixed pollutants, suggesting its probable suitability for bioremediation purposes. [ABSTRACT FROM AUTHOR]

Third-instar larvae of the goldenrod gall fly Eurosta solidaginis (Diptera: Tephritidae) survive extended periods in winter during which tissue water is frozen. Both low temperature and reduced water activity during freezing present challenges for the structural integrity of cellular lipids. Fatty acids of both phospholipids and triacylglycerols from fat body cells of E. solidaginis were analyzed throughout fall and early winter, a period that encompasses the acquisition of freeze-tolerance, to determine if adaptations to freezing include changes in fatty acid unsaturation. The five most abundant fatty acids from both fractions were (in decreasing order) oleic (40–65%), palmitoleic (18–20%), palmitic (12–17%), linoleic (5–10%), and stearic acids (4 –7%). This represents a typical complement of Dipteran fatty acids, although oleic acid levels were higher in E. solidaginis than those reported from other Dipterans (˜28%; Downer 1985). From September to November, monounsaturates increased from 59 to 70% in phospholipids at the expense of saturated fatty acids (25% –20%) suggesting activation of a Δ9-desaturase enzyme. These changes resulted in an increase in the ratio of unsaturated to saturated fatty acids (U/S) from 3.0 to 4.2, although there was no change in the average number of double bonds per fatty acid (unsaturation index, UI ≈ 1.2 in phospholipids and 0.9 in triacylglycerols throughout the season). These changes were temporally correlated to decreasing ambient temperatures and increasing larval and fat body cell freeze-tolerance. [ABSTRACT FROM AUTHOR]

The effects of temperature and pressure on Na/K-adenosine triphosphatases (Na/K-ATPases) from gills of marine teleost fishes were examined over a range of temperatures (10-25°C) and pressures (1-680 atm). The relationship between gill membrane fluidity and Na/K-ATPase activity was studied using the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH). The increase in temperature required to offset the membrane ordering effects of high pressure was 0.015-0.025°C·atm, the same coefficient that applied to Na/K-ATPase activities. Thus, temperature-pressure combinations yielding the same Na/K-ATPase activity also gave similar estimates of membrane fluidity. Substituion of endogenous lipids with lipids of different composition altered the pressure responses of Na/K-ATPase. Na/K-adenosine triphosphatase became more sensitive to pressure in the presence of chicken egg phosphatidylcholine, but phospholipids isolated from fish gills reduced the inhibition by pressure of Na/K-ATPase. Cholesterol increased enzyme pressure sensitivity. Membrane fluidity and pressure sensitivity of Na/K-ATPase were correlated, but the effects of pressure also dependent on the source of the enzyme. Our results suggest that pressure adaptation of Na/K-ATPase is the result of both changes in the primary structure of the protein and homeoviscous adaptation of the lipid environment. [ABSTRACT FROM AUTHOR]