Phallus impudicus loaded with γ-Fe2O3 as solid phase bioextractor for the preconcentrations of Zn(II) and Cr(III) from water and food samples

We investigated the application of fungus Phallus impudicus loaded γ-Fe₂O₃ nanoparticles as a biosorbent for magnetic solid phase extractions of trace levels of Zn(II) and Cr(III) ions from natural samples before their measurements by inductively coupled plasma optical emission spectrometry. The characterization of magnetized P. impudicus was performed using the scanning electron microscope, the energy dispersive X-ray and Fourier transform infrared spectroscopy. Important experimental factors were investigated. The experimental results fitted well to the Langmuir adsorption model and pseudo-second order kinetic model. Limit of detections of targeted ions by magnetic solid phase extraction method based on use of P. impudicus were found as 10.5 ngL⁻¹ and 12.6 ngL⁻¹ respectively for Cr(III) and Zn(II). The sorption capacities of the biosorbent were 22.8 mgg⁻¹ for Cr(III) and 25.6 mgg⁻¹ for Zn(II). The preconcentration factors were achieved as 100 for both of ions. RSDs for inter- and intraday precisions were found as lower than 2.0% and 2.1% respectively for both of targeted ions. The accuracy of the recommended process was tested by recovery measurements on the certificated reference materials and successfully applied for quantification recoveries of Cr(III) and Zn(II) ions from water and food samples.     

Calcium and cyclic AMP as possible mediators of neurohormone action in the hindgut of the cockroach, Leucophaea maderae

Adenosine 3′,5′-monophosphate (cyclic AMP) (10⁻⁵ g/ml) often caused a gradual increase in spotaneous contractile activity of the hindgut of the cockroach, Leucophaea maderae, and on rare occasions it would evoke a hormone-like response. However, aminophylline (2·5 × 10⁻⁴ g/ml) was capable of mimicking the neurohormone, and a concentration of 2·5 × 10⁻⁵ g/ml potentiated the contractile response evoked by the neurohormone: these responses were blocked by either the presence of 1 mM manganous ion or in a high potassium solution (162 mM). Propranolol (10⁻⁶ g/ml) and dopamine (10⁻⁴ g/ml) suppressed both spontaneous contractile events and neurohormone action. Dopamine (5 × 10⁻⁶ g/ml) also blocked action potential generation as did propranolol at 10⁻⁴ g/ml.These results lead us to suppose that cyclic AMP might serve as a mediator of neurohormone action by increasing calcium transport across the surface membrane of muscle fibres. Caffeine (2·5 × 10⁻⁴ g/ml), like aminophylline, caused a hormone-like response in normal hindguts. Even when the visceral muscles of the hindgut were depolarized in 162 mM potassium solution (without calcium), caffeine was still capable of inducing a phasic response. However, the addition of 2 mM calcium to such potassium-depolarized preparations caused a gradual increase in muscle tonus and substantially potentiated the response to caffeine.Such findings clearly implicate calcium as the mediator of excitation-contraction coupling in visceral muscle. While the interactions between the neurohormone, cyclic AMP, and calcium seem to be largely associated with the surface membrane and action potential generation.     

Potential availability of anaerobic treatment with digester slurry of animal waste for the reclamation of acid mine water containing sulfate and heavy metals

The use of an anaerobic digester slurry of cattle waste for the reclamation of acid mine water was examined. When the digester slurry was mixed with acid mine water, anaerobic digestion, including sulfate reduction and methanogenesis, was enhanced. In the mixture of acid mine water and the digester slurry, sulfate reduction proceeded without diminishing methanogenesis. The digester slurry and its supernatant (SDF-sup) showed a significant capacity to act as a strong alkaline reagent, and the pH of the acid mine water was markedly elevated by the addition of the digester slurry of SDF-sup even at the low ratio of 1% (v/v). Precipitation of heavy metals in the acid mine water occurred as the pH was elevated by the addition of SDF-sup. When the digester slurry was added at the ratio of 5% (v/v) to acid mine water which had been pretreated with SDF-sup, the rate of sulfate reduction increased with increasing the concentration of sulfate in the mixture up to about 1,400 mg·l⁻¹. In acid mine water pretreated with SDF-sup and supplemented with the digester slurry at the ratio of 5% (v/v), the maximum amount of sulfate reduced within 20 d of incubation was about 1,000 mg·l⁻¹, and the maximum rate of sulfate reduction was about 120 mg SO₄²⁻·l⁻¹·d⁻¹.     

ATP-dependent chloride transport in plasma membrane vesicles from Aplysia intestine

A Cl⁻-stimulated ATPase activity, which is sensitive to both thiocyanate and vanadate, has been localized to the plasma membrane of Aplysia enterocytes. Utilizing plasma membrane vesicles from Aplysia enterocytes, ATP stimulated Cl⁻ uptake to approximately 2.5-times that of control in a Na⁺, K⁺ and HCO₃⁻-free medium. This ATP-dependent Cl⁻ uptake was sensitive to both thiocyanate and vanadate. These results are consistent with the hypothesis that the active Cl⁻ absorptive process in Aplysia intestine could be a Cl⁻-stimulated ATPase found in the enterocyte plasma membrane.     

Regulation of intestinal hPepT1 (SLC15A1) activity by phosphodiesterase inhibitors is via inhibition of NHE3 (SLC9A3)

The H⁺-coupled transporter hPepT1 (SLC15A1) mediates the transport of di/tripeptides and many orally-active drugs across the brush-border membrane of the small intestinal epithelium. Incubation of Caco-2 cell monolayers (15 min) with the dietary phosphodiesterase inhibitors caffeine and theophylline inhibited Gly-Sar uptake across the apical membrane. Pentoxifylline, a phosphodiesterase inhibitor given orally to treat intermittent claudication, also decreased Gly-Sar uptake through a reduction in capacity (V_max) without any effect on affinity (K_m). The reduction in dipeptide transport was dependent upon both extracellular Na⁺ and apical pH but was not observed in the presence of the selective Na⁺/H⁺ exchanger NHE3 (SLC9A3) inhibitor S1611. Measurement of intracellular pH confirmed that caffeine was not directly inhibiting hPepT1 but rather having an indirect effect through inhibition of NHE3 activity. NHE3 maintains the H⁺-electrochemical gradient which, in turn, acts as the driving force for H⁺-coupled solute transport. Uptake of β-alanine, a substrate for the H⁺-coupled amino acid transporter hPAT1 (SLC36A1), was also inhibited by caffeine. The regulation of NHE3 by non-nutrient components of diet or orally-delivered drugs may alter the function of any solute carrier dependent upon the H⁺-electrochemical gradient and may, therefore, be a site for both nutrient-drug and drug-drug interactions in the small intestine.     

Exploitation of micellar medium for photochemical-spectrofluorimetric flow-injection determination of fenvalerate

A photochemical flow-injection methodology for the fluorimetric determination of fenvalerate, a nonfluorescent pyrethroid pesticide, is proposed. The sample was irradiated by ultraviolet light inside a reaction coil in a nonstop mode and the photodegradation products were monitored by spectrofluorimetry at λ_exc=277 nm, λ_em=329 nm. The exploitation of a micellar medium resulted in a pronounced fluorescence enhancement with a concomitant tenfold sensitivity improvement. Several surfactants were evaluated, and best results were obtained with sodium dodecylsulphate (SDS). The calibration plot was linear within 2.0×10⁻⁶ and 1.0×10⁻⁵ mol l⁻¹ fenvalerate. The proposed system is very stable, handles 30 samples h⁻¹ and requires only 60 μmol SDS per determination. The detection limit is 5×10⁻⁷ mol l⁻¹. The method was evaluated in the determination of fenvalerate in tap water.     

Immunodetection of a 90 000-Mr polypeptide related to yeast plasma membrane ATPase in plasma membrane from maize shoots

Maize shoot plasma membranes were prepared using either polyethyleneglycol (PEG)-dextran phase partition or centrifugation through a 30% sucrose cushion. The ATPase specific activity of membranes obtained with the phase partition method (1.4 μmol P_i · min⁻¹ · mg⁻¹ protein) was twice that of those prepared with the sucrose cushion method. After solubilization by lysolecithin and precipitation by ammonium sulfate, ATPase activities of the order of 3.0–3.5 μmol P_i · min⁻¹ · mg⁻¹ were obtained. A polypeptide of M_r = 90 000 was enriched during ATPase purification.Antibodies against pure plasma membrane ATPase from Saccharomyces cerevisiae inhibited the plant ATPase activity. Immunodetection during purification of the plant enzyme strongly supported the conclusion that the polypeptide of M_r = 90 000 belongs to plant plasma membrane ATPase.     

Sedimentation of Nodularia spumigena and distribution of nodularin in the food web during transport of a cyanobacterial bloom from the Baltic Sea to the Kattegat

Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 10³ cells ml⁻¹), and cells (4.2 10³ cells ml⁻¹) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l⁻¹), samples of sedimenting material (a toxin accumulation rate of 20 μg m^-2 day⁻¹), zooplankton (up to 0.1 ng ind.⁻¹ in copepods), blue mussels (70–230 μg kg⁻¹ DW), pelagic and benthic fish (herring (1.0–3.4 μg kg⁻¹ DW in herring muscle or liver) and flounder (1.3-6.2 μg kg⁻¹ DW in muscle, and 11.7-26.3 μg kg⁻¹ DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day⁻¹ at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters.     

A comparison of models for predicting slurry production on a pig farm

Three methods of predicting slurry production were compared with the volumes actually produced on a 150 sow breeding and fattening pig unit. The methods were based on (a) feed, water and slurry relationships measured in crated and penned pigs; (b) values given in the literature and used by ADAS to predict slurry outputs from pigs; (c) a method based on the digestibility of feed and of water measured at the actual piggery. Method (a) was not found appropriate because of the high overall water:meal ratio found in the unit (13:1). Method (b) was able to predict dry matter production accurately but underestimated the volume produced unless the ADAS allowance of 0·5 litres pig⁻¹ day⁻¹ for washing water and leaking drinkers was increased to 10 litres. Method (c) was the best method for estimating volume but underestimated dry matter production. Combining the better aspects of methods (b) and (c) allows volume, dry matter production and dry matter concentration to be predicted satisfactorily. The daily movements of slurry from the reception pit were very variable. The use of water meters on pig units is recommended to identify wastage.     

The physiological and morphological features of M. thyroarytenoideus internus and externus of the rabbit in relation to the activity of the vocal cord

• 1.1. Electrical, mechanical and morphological properties of M. thyroarytenoideus internus and externus (Int. M. and Ext. M., respectively) of the rabbit were investigated.
• 2.2. The membrane potentials of Int. M. and Ext. M. were −80.1 and −77.2 mV, respectively, and both muscles generated the overshoot action potentials by electrical stimulation. The electrical properties of both muscles were essentially the same.
• 3.3. The critical membrane potential to trigger the potassium-induced (K⁺) contracture was −52mV in Int. M. On the other hand, in Ext. M., the contracture was hardly developed, but when it was developed, the critical membrane potential was −25mV. The K⁺ contracture was facilitated in both muscles by substitution of Cl⁻ by Br⁻, NO⁻₃ or SCN⁻.
• 4.4. Both muscles generated twitch contraction by electrical stimulation, and Ext. M. showed faster contraction than Int. M.
• 5.5. Active state for the tension development of both muscles was compared. The decay time of Ext. M. was much shorter than that of Int. M. Substitution of Cl⁻ by foreign anions (Br⁻, NO⁻₃ and SCN⁻) and treatment with caffeine enhanced the amplitude and prolonged the duration of the active state of both muscles.
• 6.6. Histochemical analysis (succinic dehydrogenase and myosin ATPase staining methods) revealed that Ext. M. was composed of solely white fibres, while Int. M. was composed of several types of fibres. The electron microscopic observation revealed that Int. M. was composed of red and intermediate fibres and Ext. M. was of white ones.
• 7.7. The results suggest that the differences of mechanical properties were presumably due to the differences of development of sarcoplasmic reticulum in both muscle tissues. The specific features of these muscles were discussed in relation to vocal cord activity.

     

The distribution of lead in the soils and herbage of West Pembrokeshire

Lead has been determined in top and subsoil samples from over 500 sites in West Pembrokeshire. Topsoils contain from <1 to 356 μg g⁻¹ Pb with a mean of 39 μ g⁻¹ Pb while subsoils contain 0 to 172 μg g⁻¹ Pb with a mean value of 22 μg g⁻¹ Pb.Lead has also been determined in herbage samples from north west Pembrokeshire and in these, the Pb contents range from <1 μg g⁻¹ to 9 μg g⁻¹ but most samples contain <2 μg g⁻¹. Maximum contents of Pb were found in March when samples were taken at the same site throughout the growing season.Soil samples showed maximum Pb contents around towns but this pattern was not duplicated by herbage.     

Properties of glucose-dehydrogenase-poly(ethylene glycol)-NAD conjugate as an NADH-regeneration unit in enzyme reactors

Glucose-dehydrogenase-poly(ethylene glycol)-NAD conjugate (GlcDH-PEG-NAD) was prepared and its kinetic properties as an NADH-regeneration unit were investigated. The conjugate has about two molecules of active and covalently linked NAD per tetramer. The specific activity of the enzyme moiety of the conjugate in the presence of exogenous NAD is about 77% of that of the native enzyme, and this decrease is mainly due to the decrease in the V_max value. The conjugate has the same pH-stability profile as the native enzyme and an internal activity of 0.26s⁻¹ (as a monomer); its NAD moiety has similar coenzyme activity to poly(ethylene glycol)-bound NAD. These results indicate that GlcDH-PEG-NAD can be used as an NADH-regeneration unit for many dehydrogenase reactions. The coupled reaction of GlcDH-PEG-NAD and lactate dehydrogenase was then studied. The specific activity of the conjugate is 1.1 s⁻¹ (as a tetramer), the recycling rate of the active NAD moiety is 0.54 s⁻¹, and the apparent K_m value for glucose is 24 mM. Kinetically, lactate dehydrogenase behaves like a substrate with an apparent K_m value of 1.8 units·ml⁻¹ in this coupled reaction system with low coenzyme concentration. l-Lactate was continuously produced from pyruvate in a reactor with a PM10 ultrafiltration membrane, and containing GlcDH-PEG-NAD and lactate dehydrogenase. GlcDH-PEG-NAD proved to be applicable in continuous enzyme reactors as an NADH-regeneration unit with a large molecular size.     

Proton production from nitrogen transformation drives stream export of base cations in acid-sensitive forested watersheds

The biogeochemical cycles of nitrogen (N) and base cations (BCs), (i.e., K⁺, Na⁺, Ca²⁺, and Mg²⁺), play critical roles in plant nutrition and ecosystem function. Empirical correlations between large experimental N fertilizer additions to forest ecosystems and increased BCs loss in stream water are well demonstrated, but the mechanisms driving this coupling remain poorly understood. We hypothesized that protons generated through N transformation (PPR_N)—quantified as the balance of NH₄⁺ (H⁺ source) and NO₃⁻ (H⁺ sink) in precipitation versus the stream output will impact BCs loss in acid-sensitive ecosystems. To test this hypothesis, we monitored precipitation input and stream export of inorganic N and BCs for three years in an acid-sensitive forested watershed in a granite area of subtropical China. We found the precipitation input of inorganic N (17.71 kg N ha⁻¹ year⁻¹ with 54% as NH₄⁺–N) was considerably higher than stream exported inorganic N (5.99 kg N ha⁻¹ year⁻¹ with 83% as NO₃⁻–N), making the watershed a net N sink. The stream export of BCs (151, 1518, 851, and 252 mol ha⁻¹ year⁻¹ for K⁺, Na⁺, Ca²⁺, and Mg²⁺, respectively) was positively correlated (r = 0.80, 0.90, 0.84, and 0.84 for K⁺, Na⁺, Ca²⁺, and Mg²⁺ on a monthly scale, respectively, P < 0.001, n = 36) with PPR_N (389 mol ha⁻¹ year⁻¹) over the three years, suggesting that PPR_N drives loss of BCs in the acid-sensitive ecosystem. A global meta-analysis of 15 watershed studies from non-calcareous ecosystems further supports this hypothesis by showing a similarly strong correlation between ∑BCs output and PPR_N (r = 0.89, P < 0.001, n = 15), in spite of the pronounced differences in environmental settings. Collectively, our results suggest that N transformations rather than anions (NO₃⁻ and/or SO₄²⁻) leaching specifically, are an important mediator of BCs loss in acid-senstive ecosystems. Our study provides the first definitive evidence that the chronic N deposition and subsequent transformation within the watershed drive stream export of BCs through proton production in acid-sensitive ecosystems, irrespective of their current relatively high N retention. Our findings suggest the N-transformation-based proton production can be used as an indicator of watershed outflow quality in the acid-sensitive ecosystems.     

The growth dynamics of Halophila hawaiiana

A functional growth model was developed for Halophila hawaiiana Doty and Stone, based on its regular plastochrone interval, and the relationship between leaf area and plant biomass. The model allows estimates of biomass, productivity and turnover from easily collected field samples. From these samples, the number of actively growing apical buds, total leaf number and total leaf area for a unit area were determined. This model was applied to a meadow in Kaneohe Bay, Oahu. The mean biomass was 104.25 g dry wt. m⁻² and the productivity 7.11 g dry wt. m⁻² day⁻¹. The turnover time was 14.7 days.     

Establishment and application of hyperbranched rolling circle amplification coupled with lateral flow dipstick for the sensitive detection of Karenia mikimotoi

The dinoflagellate Karenia mikimotoi is a noxious and harmful algal bloom (HAB)-forming microalga. Establishing a rapid, accurate, and sensitive method of detecting this harmful alga is necessary to provide warnings of imminent HABs through field monitoring. Here, an isothermal amplification technique combined with a rapid analytical method for nucleic acid-based amplified products, i.e., hyperbranched rolling circle amplification (HRCA) coupled with lateral flow dipstick (LFD), hereafter denoted as HRCA-LFD, was established to detect K. mikimotoi. The HRCA-LFD assay relied on a padlock probe (PLP) targeting DNA template and an LFD probe targeting PLP. The sequenced internal transcribed spacer of K. mikimotoi through molecular cloning was used as the target of PLP. The optimized HRCA conditions was determined to be as follows: PLP concentration, 20 pM; ligation temperature, 65 °C; ligation time, 10 min; amplification temperature, 61 °C; and amplification time, 30 min. The developed HRCA-LFD assay was specific for K. mikimotoi, displaying no cross-reactivity with other common microalgae. Sensitivity-comparison tests indicated that HRCA-LFD assay was 100-fold more sensitive than PCR, with a detection limit of 0.1 cell mL⁻¹ when used to analyze spiked field samples. The analysis with field samples also indicated that HRCA-LFD assay was suitable for samples with a target cell density range of 1–1000 cells mL⁻¹. All of these results suggested that HRCA-LFD assay is an alternative method for the sensitive and reliable detection of K. mikimotoi from marine water samples.     

Lactic acid from acid whey permeate in a membrane recycle bioreactor

Whey permeate was obtained by ultrafiltration of cottage cheese whey and supplemented with yeast extract. The lactose in the permeate was converted into lactic acid by Lactobacillus bulgaricus in a high-performance membrane bioreactor configured in the cell recycle mode. At a cell concentration of 10 g l⁻¹, optimum productivity of lactic acid was 35 g l⁻¹ h⁻¹. Increasing the cell concentration to 30 g l⁻¹ enabled the use of a dilution rate of 1 h⁻¹ with complete substrate utilization. At 60 g l⁻¹, productivity was over 80 g l⁻¹ h⁻¹ with complete substrte utilization; this is vastly superior to conventional batch fermentations.     

The Structure of a Macroinvertebrate Community in a Northern German Lake Outlet (Lake Belau,Schleswig-Holstein) with Special Emphasis on Abundance,Biomass and Secondary Production

The structure of macroinvertebrate communities was studied at I I sampling sites of the outlet of Lake Belau in the lowlands of northern Germany. To describe the structures of macrobenthic animal communities three different units were examined: abundance, biomass, and secondary production. 112 taxa were collected from the entire stream. The numbers of species ranged from 31 (fine sand) to 70 (submerged macrophytes). For the stream, average macroinvertebrate density was 18.400 ind. M⁻¹. Density was highest at the macrophytes amounting to 35,630 individuals per m², and lowest in the pure sand with only 3,900 ind. M⁻². Average biomass (dry mass) was 194 g DM m⁻² varying from 9.8 (peat) to 381 g DM m⁻² (gravel with mollusk shells near the upstream lake). For the stream, average annual production was 129 g DM m⁻² varying from 15 (peat) to 286 g DM m⁻² (macrophytes). The highest values for each unit were found in stream sections with gravel and submerged macrophytes. Lower values occured in sections that contained peat and sand. Usually, a single structure of the macroinvertebrate community was dominated by less than ten taxa, which varied at each sampling site depending on the units observed.     

Binding characteristics of estrone,estradiol and estriol to the human myometrial estrogen receptor

The human myometrial estrogen receptor in cytosol from pre-menopausal uterine samples has been characterized. At 0° estradiol (K_D 0.38 × 10⁻¹⁰M) has the highest affinity to the receptor followed by estrone (K_D 0.76 × 10⁻¹⁰M) and estriol ((K_D 1.33 × 10⁻¹⁰M). The association rate constant is 2.8 × 10⁵M⁻¹s⁻¹ for estradiol, 2.1 × 10⁵M⁻¹s⁻¹ for estrone and 0.79 × 10⁵M⁻¹s⁻¹ for estriol. The dissociation constants and the association rate constants increase with temperature. The calculated thermodynamic parameters indicate a positive change in entropy for the formation of the estrogen receptor complex.The cytoplasmic estrogen receptor has a sedimentation coefficient of 4 s in low salt sucrose gradients. In buffer containing diisopropylfluorophosphate (DFP) to inhibit proteolytic activity the estrogen receptor complex sediments solely as an 8 s peak if [³H]-estradiol is added to the buffer prior to homogenization and the tissue sample is used immediately after hysterectomy. Estrogen receptor complexes that sediment at 4 s and 8 s are found if [³H]-estradiol is omitted from the homogenization buffer and instead added after the cytosol preparation. Most likely a protease is involved the activity of which is not completely inhibited by DFP.Addition of low concentrations of Cu²⁺ (10 μM) to the cytosol increases the dissociation constant and decreases the estrogen-binding capacity of the receptor. The rate of association is reduced in the presence of 20 μM Cu²⁺. The estrogen receptor complexes do not show any change in their sedimentation profiles in the presence of Cu²⁺.     

Specificity and distribution of antigenic determinants on the polyoma virus capsid and nature of the reaction of immunoglobulin G antibody with the capsid surface.

Antisera to the LP and SP34 strains of polyoma virus have been prepared and their reactions with purified virions studied by double diffusion in agar and direct assay of antibody binding. One or more common antigenic determinants appear on the capsids of both strains. The form of this determinant varies slightly on each of the strains tested. The SP34 strain also carries its own strain-specific antigenic determinant. Both strains of virus were able to bind 150 anti-LP IgG³ molecules per virion and 50 anti-SP IgG molecules per virion. The slow rate of dissociation of bound IgG antibody (k_dissociation = 2 × 10⁻⁶ s⁻¹), and the rapid rate of antibody binding (k_dissociation = 2 × 10⁷m⁻¹ s⁻¹), suggest that IgG antibody is bound to the capsid surface through two antigen-antibody bonds. 50 anti-SP IgG molecules per capsid, divalently bound, completely inhibit the binding of 150 anti-LP IgG molecules, and vice versa. Consideration of the symmetry and molecular dimensions of the IgG molecule and the polyoma virus capsid leads to a model of the divalent interaction of IgG antibody with the common antigenic determinant(s). In this model, one species of antibody binds divalently to opposed subunits of a hexamer morphological unit. The other species of antibody binds divalently to the subunits on either side of the point of tangency of any two morphological units.     

Domoic acid in a marine pelagic food web: Exposure of southern right whales Eubalaena australis to domoic acid on the Península Valdés calving ground,Argentina

The gulfs that surround Península Valdés (PV), Golfo Nuevo and Golfo San José in Argentina, are important calving grounds for the southern right whale Eubalaena australis. However, high calf mortality events in recent years could be associated with phycotoxin exposure. The present study evaluated the transfer of domoic acid (DA) from Pseudo-nitzschia spp., potential producers of DA, to living and dead right whales via zooplanktonic vectors, while the whales are on their calving ground at PV. Phytoplankton and mesozooplankton (primary prey of the right whales at PV and potential grazers of Pseudo-nitzschia cells) were collected during the 2015 whale season and analyzed for species composition and abundance. DA was measured in plankton and fecal whale samples (collected during whale seasons 2013, 2014 and 2015) using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-nitzschia was present in both gulfs with abundances ranging from 4.4 × 10² and 4.56 × 10⁵ cell l⁻¹. Pseudo-nitzschia australis had the highest abundance with up to 4.56 × 10⁵ cell l⁻¹. DA in phytoplankton was generally low, with the exception of samples collected during a P. australis bloom. No clear correlation was found between DA in phytoplankton and mesozooplankton samples. The predominance of copepods in mesozooplankton samples indicates that they were the primary vector for the transfer of DA from Pseudo-nitzschia spp. to higher trophic levels. High levels of DA were detected in four whale fecal samples (ranging from 0.30 to 710 μg g⁻¹ dry weight of fecal sample or from 0.05 and 113.6 μg g⁻¹ wet weight assuming a mean water content of 84%). The maximum level of DA detected in fecal samples (710 μg DA g⁻¹ dry weight of fecal sample) is the highest reported in southern right whales to date. The current findings demonstrate for the first time that southern right whales, E. australis, are exposed to DA via copepods as vectors during their calving season in the gulfs of PV.