Determination of selenium and its compounds in marine organisms

In this study, we investigate the type and quantity of selenium compounds in fish and marine organisms, using ion-pair reversed phase LC–ICP-MS, developed and applied for the analysis of Atlantic cod, Atlantic salmon, Greenland halibut, Atlantic herring, blue mussel, common crab, scallop, calanus, and Euphasia super. Of the samples examined, the lowest level of selenium was found in farmed Atlantic salmon (0.17 mg Se kg⁻¹ dm). The total selenium extraction efficiency by phosphate buffer was 2.5 times higher in sea plankton and shellfish samples than in fish samples. Analysis of Se species in each hydrolysate obtained by proteolysis showed the presence of selenomethionine, which constituted 41.5% of the selenium compounds detected in hydrolysates of Atlantic herring and 98.4% of those in extracts of Atlantic salmon. Inorganic compounds, such as selenates and selenites, were detected mainly in sea plankton and shellfish samples (<0.13 mg Se kg⁻¹ wm), although no correlation was found between the presence of inorganic compounds and total selenium concentration. The accuracy of the total selenium determination was validated using a certified reference material (oyster tissue (NIST 1566b)). A lyophilised powder of cod (Gadus morhua) was used to validate speciation analysis, enzymatic hydrolysis of lyophilised powder of cod recovered 54 ± 6% of total selenium, and SeMet constituted 83.5 ± 5.28% of selenium detected in hydrolysates. The chromatographic detection limits were, respectively, 0.30 ng mL⁻¹, 0.43 ng mL⁻¹, 0.54 ng mL⁻¹, 0.55 ng mL⁻¹, 0.57 ng mL⁻¹ and 0.72 ng mL⁻¹ for selenate, selenomethionine, selenite, Se-methyl-selenocysteine, selenocystine and selenomethionine selenoxide.The data on selenium concentrations and speciation presented here could be useful in estimating levels of selenium intake by seafood consumption.     

Membrane lipid composition and overwintering site of the wading bird Calidris alpina

• 1.1. Two subspecies of the wading bird, Calidris alpina, differ in overwintering site; C. alpina alpina overwinters in Britain at water temperatures of ≈ 7°C, and C. alpina schinzii overwinters in Africa, wading in water ≈ 15°C.
• 2.2. Phosphoglyceride fatty acids from the uninsulated leg tissues of C. alpina alphina have a significantly higher U/S ratio (weight per cent of monoenes + PUFA/weight per cent of saturates) than those from C. alpina schinzii, due to the enrichment of monoenes at the expense of saturates.
• 3.3. The accumulation of monoenes in the cold-water wader may be an adaptation to conserve the fluidity of cellular membranes in exposed extremities.

     

Seasonal movements of crayfish in a fluctuating wetland: implications for restoring wading bird populations

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The adaptive significance of stealing in a marine bird and its relationship to parental quality

Kleptoparasitism (food theft) is a tactic used opportunisticallyby many foraging birds, but little is known about its fitnessbenefits. Here we show that habitual kleptoparasitism by individualparent roseate terns (Sterna dougallii) is associated with consistentlysuperior reproductive performance relative to nonkleptoparasitic("honest") parents, as measured by growth and survival to fledgingamong their offspring. In broods of two, both chicks of kleptoparasiticparents exhibited superior growth performance during the middleand later stages of the rearing period, relative to chicks ofhonest parents. This difference was especially pronounced insecond-hatched chicks, whose survival is highly variable amongyears and dependent on food availability. Over a 10-year period,average productivity (number of chicks fledged per pair) wassignificantly higher among kleptoparasites than among honestparents, with a larger relative difference during years of foodshortage. Our study indicates that kleptoparasitism in roseateterns is an important component of parental quality and providesthe first evidence that food stealing is associated with enhancedfitness in a facultatively kleptoparasitic seabird.     

The binding of selenium to the lipids of two unicellular marine algae

Axenic cultures of the green algae $\text{Dunaliella}\text{primolecta}$ and red algae $\text{Porphyridium}\text{cruentum}$ were grown in the presence of sublethal quantities of selenite. All purified lipids from both algae were found to contain bound selenium, except for saturated hydrocarbons. Of the lipids which contain selenium, carotenoid pigments contain the greatest concentrations. Lipid-associated selenium is not metabolically incorporated. The selenium is probably non-covalently bound to the lipids.     

Responses of an African wading bird community to resource pulses are related to foraging guild and food‐web position

1. The immediate impacts of nutrient inputs on aquatic systems are well documented, but the ways in which resource pulses affect the wider food web of water‐associated vertebrates remain obscure. 2. We monitored the wading bird community of Barberspan, a natural freshwater lake and Ramsar wetland in South Africa, before, during and after the addition of a pulse of nutrients in the form of a sewage overspill from an upstream processing facility. We counted waders at 13 points around the lake over 3 years, every 2 months from March 2007 to March 2010, and sampled water quality during all counting periods from January 2008 to January 2010. 3. We used our data to test the hypothesis that wading birds that forage directly at lower trophic levels and/or on prey populations that have fast turnover rates, such as those of phytoplankton and invertebrates, will be more heavily influenced by nutrient addition than birds that forage on species with lower turnover rates and/or at higher trophic levels (such as frogs and fish). 4. During the sampling period Barberspan experienced a significant, nutrient‐driven decline and subsequent recovery in dissolved oxygen and pH. This trend was mirrored by significant changes in the wading bird community. Partial Mantel tests and Canonical Correspondence Analysis (CCA) showed that the nutrient pulse had marked short‐term, negative impacts on both the diversity and the abundance of medium‐sized, shoreline foragers such as scolopacids (e.g. sandpipers). 5. Our analysis supports the proposal that both food‐web position and the turnover rate of the prey population are strong influences on ecological responses to resource pulses. Analysis of time series of principal components that describe community composition suggested that recovery of the prey base was rapid and that the bird community was able to respond via immigration. These results must, of course, be considered provisional in the absence of replicated experimental data. 6. More generally, we interpret our results as suggesting that two different mechanisms act in different directions to determine the sensitivity of secondary and tertiary consumers to changes in their prey. First, for ‘earlier’ consumers (i.e. that forage lower in the food web), there are (on average) fewer generalist consumers and fewer stored nutrients in the intervening trophic levels. This increases the sensitivity of earlier consumer populations to changes in the composition of the primary consumer community. Second, the dynamics of prey populations lower in the food web tend to be faster, making recovery faster and serving to decrease the sensitivity of earlier consumers to perturbations. These dynamics may obscure the impacts of nutrient pulses in cases where additional analysis of system trajectories is not undertaken.     

Toxic levels of selenium in enzymes and selenium uptake in tissues of a marine fish

Acute toxicity of selenium as selenite inZosterisessor ophiocephalus by ip injection was studied. The 50% lethal dose and 50% lethal time were measured to be 0.29 ppm and 96 h, respectively. Se concentrations in liver, gill, skin and muscle, and Cyt. P450 level, Se-GPx, and Total GPx enzyme activities in liver were also assessed at different doses and times after injection. Starting at 0.3 ppm injected dose, enzyme activities and Se concentration in tissues but not in muscle, showed significant differences from the control group. A threshold behavior was inferred. Normal conditions of enzyme activities and Se concentration in tissues were restored about 1 wk after injection. Biological elimination half-lives were about 2 d for liver and gill, and 5 d for skin.     

Distribution of selenium in marine animals: relationship to diet

The chemical form of selenium in the muscle tissues of marine animals in relation to diet has been examined. Inorganic selenium concentrations in all muscle tissues were below the detection limits of the analytical method employed (0.001 mg/kg). Selenium was found to be associated in all tissues predominantly with insoluble proteins. Lipid-soluble and ethanol-soluble selenium constituted less than 18% of the selenium present in tissues and was independent of diet.     

Mutagenic activity of selenium compounds

The mutagenicities of selenate (SeO₄²⁻) and selenite (SeO₃²⁻) were determined by two bacterial assay systems: Kada's rec-assay and Ames's Salmonella test. In both assays, these compounds were found to be weak mutagens. In the Salmonella test, selenate (0.05 revertants/nmole) and selenite (0.2 revertants/nmole) gave rise to base-pair substitution.     

Biological effects of selenium compounds with a particular attention to the ontogenetic development

Selenium is a trace element that is essential for living organism. Its beneficial effect is, however, expressed in a very narrow dosage range: the high and low doses of selenium are connected with pathological manifestations. The toxicity depends on the chemical form of selenium, state of organism, interactions with heavy metals and on the stage of ontogenetic development. Whereas one dose of sodium selenite (20 micromol/kg b.w.) is lethal in adult rats, suckling rats are entirely resistant. However, within one week after administration of the same dose, cataract of eye lens developed. The highest incidence of cataract was observed in 10-day-old animals and it decreased until day 20. From postnatal day 20 to day 40 the rats were resistant to both the lethal and cataractogenic effects of selenium. The incidence of cataract may be suppressed by premature weaning, lower hydration of suckling, change of water soluble/water insoluble lens protein ratio, thyroxine treatment, and by interaction with mercury. By means of its oxidative and reduction properties, selenium is involved in the maintenance of the cell redox homeostasis. Typical example is its possible cardioprotective effect: selenium decreased number of arrhythmias, reduced infarct size and improved the contractile recovery after ischemia/reperfusion injury. Selenium supplementation may thus increase cardiac tolerance to ischemic damage.     

Mutagenic activity of selenium compounds.

The mutagenicities of selenate (SeO2/4-) and selenite (SeO2/3-) were determined by two bacterial assay systems: Kada's rec-assay and Ames's Salmonella test. In both assays, these compounds were found to be weak mutagens. In the Salmonella test, selenate (0.05 revertants/nmole) and selenite (0.2 revertants/nmole) gave rise to base-pair substitution.     

Mechanism for proliferation inhibition by various selenium compounds and selenium-enriched broccoli extract in rat glial cells

The objective of this study was to investigate the differential effects of various selenium (Se) compounds and Se-enriched broccoli extracts on cell proliferation and the possible mechanism responsible for the Se-induced growth inhibition. C6 rat glial cells were incubated with graded concentrations up to 1000 nM of selenite, selenate, selenomethionine (SeM), Se-methyl-selenocysteine (SeMCys), high-Se broccoli (H-SeB) extract or low-Se broccoli (L-SeB) extract for 24 and 48 h. MTT results indicated that all Se sources and levels examined inhibited C6 cell proliferation at 48 h. The results from cell cycle progression and apoptosis analysis indicated that SeM, SeMCys, H-SeB or L-SeB treatments at the concentration of 1000 nM reduced the cell population in G₀/G₁ phase, but induced G₂/M phase arrest and increased apoptosis and secondary necrosis in C6 cells at 24 h. The populations of apoptotic cells and secondary necrotic cells were increased by all Se sources examined. The COMET assay indicated that there was no significant DNA single-strand break found for all Se treatments in C6 cells for 48 h. In addition, the Se-induced proliferation inhibition may involve a hydrogen peroxide (H₂O₂)-dependent mechanism with elevated cellular glutathione peroxidase (cGPX) activity. Both H-SeB and L-SeB inhibited C6 cell proliferation but H-SeB was less inhibitory than L-SeB. The proliferation inhibition by H-SeB in C6 cells is apparently related to the increased H₂O₂ with the elevated cGPX activity, but the inhibition by L-SeB was H₂O₂-independent without change in cGPX activity.     

In vivo bioavailability of selenium in enriched Pleurotus ostreatus mushrooms

The in vivo bioavailability of Se was investigated in enriched Pleurotus ostreatus mushrooms. A bioavailability study was performed using 64 Wistar male rats separated in 8 groups and fed with different diets: without Se, with mushrooms without Se, with enriched mushrooms containing 0.15, 0.30 or 0.45 mg kg(-1) Se and a normal diet containing 0.15 mg kg(-1) of Se using sodium selenate. The experiment was performed in two periods: depletion (14 days) and repletion (21 days), according to the Association of Official Analytical Chemists. After five weeks, the rats were sacrificed under carbon dioxide, and blood was drawn by heart puncture. Blood plasma was separated by centrifugation. The total Se concentration in the plasma of rats fed with enriched mushrooms was higher than in rats fed with a normal diet containing sodium selenate. The plasma protein profiles were obtained using size exclusion chromatography (SEC) and UV detectors. Aliquots of effluents (0.5 mL per minute) were collected throughout in the end of the chromatographic column. However, Se was determined by graphite furnace atomic absorption spectrometry (GF AAS) only in the aliquots where proteins were detected by SEC-UV. The plasma protein profile of rats fed with different diets was similar. The highest Se concentration was observed in a peptide presenting 8 kDa. Furthermore, the higher Se concentration in this peptide was obtained for rats fed with a diet using enriched mushrooms (7 μg L(-1) Se) compared to other diets (2-5 μg L(-1) Se). These results showed that Se-enriched mushrooms can be considered as an alternative Se food source for humans, due to their high bioavailability.     

Chemotaxis of Bradyrhizobium japonicum to various organic compounds

The investigation of the chemotactic response of Bradyrhizobium japonicum to amino acids, carbohydrates, multiatomic alcohols, organic acids, and soybean extracts showed that the extracts of some soybean varieties (Chernoburaya and Beskluben'kovaya) contain repellents. This indicates that the soybeans of host plants contain effectors that may play a role at the early stages of their interaction with nodule bacteria.