Technical communication: Determination of cuprous ions in bacterial leachates and for environmental monitoring

A sensitive and precise spectrophotometric method has been developed for the determination of copper(I) in bacterial leach liquors produced by the action of Thiobacillus ferrooxidans and T. thiooxidans on copper ores. In this method bicinchoninic acid (BCA) has been used as the chromogenic reagent which produces a stable purple complex with Cu(I) which was found to obey Beer's Law and with _max at 560 nm. The coloured complex has a molar extinction coefficient () value of 6.6 × 10³ l mol^–1 cm^–1; specific absorptivity () value of 0.104 ml^–1 g cm^–1 and the Sandell sensitivity (S) value was 0.0096 g cm². Optimal conditions for development of coloration/sensitivity were determined. Interferences due to cations and anions were investigated and various masking agents for alleviating their inhibition were studied. The method has been found very useful in determining ratios of Cu(I) to Cu(II) in bacterial leach liquors and should play a significant role in determining the reaction mechanisms of biological leaching and for environmental monitoring.     

Is birch a suitable reference in estimating dinitrogen fixation in alders by isotope dilution?

Seedlings ofAlnus incana (nodulated and non-nodulated) andBetula papyrifera were fertilized with varying amounts (0, 10, 25, 50, 100, 250 and 500 g N g^–1 soil) of labelled ammonium-N or nitrate-N ( 5.2 A% excess¹⁵N as ammonium sulphate or potassium nitrate). After 4 months in the greenhouse,¹⁵N excess in the plants were determined and an isotope dilution equation was applied to determine the percent of biomass N fixed by theA. incana/Frankia system. When ammonium was used as the sole N source and birch as the non-fixing reference, N-fixation accounted for 95%, 87% and 60% of the plant nitrogen yields with 10, 25 and 50 g N g^–1 rates, additions respectively. At the 100 g N g^–1 fertilization and above N-fixation accounted for less than 10% of the N yield. Similar results were obtained when non-nodulatedA. incana was used as non-fixing reference. With nitrate as the sole N source, N-fixation accounted for 98%, 97%, 97%, 86%, 56% and 12% of N yield with 10, 25, 50, 100, 250 and 500 g N g^–1 additions respectively. These values were similar for both types of reference plants. The direct isotope dilution method was compared to that of the total nitrogen difference method. There was good agreement between the two methods up to 50 g N g^–1 for ammonium and up to 100 g N g^–1 for nitrate. The difference method produced negative values at high concentrations of nitrogen fertilization. Again similar results were obtained by the two reference plants. The results indicate that birch can be used as a non-fixing control in isotope dilution studies but that care must be exercised in selecting the type and quantity of labelled nitrogen fertilizer.     

Chemolithotrophic growth ofDesulfovibrio desulfuricans with hydrogen coupled to ammonification of nitrate or nitrite

Two of nine sulfate reducing bacteria tested,Desulfobulbus propionicus andDesulfovibrio desulfuricans (strain Essex 6), were able to grow with nitrate as terminal electron acceptor, which was reduced to ammonia. Desulfovibrio desulfuricans was grown in chemostat culture with hydrogen plus limiting concentrations of nitrate, nitrite or sulfate as sole energy source. Growth yields up to 13.1, 8.8 or 9.7 g cell dry mass were obtained per mol nitrate, nitrite or sulfate reduced, respectively. The apparent half saturation constants (K _s) were below the detection limits of 200, 3 or 100 mol/l for nitrate, nitrite of sulfate, respectively. The maximum growth rates {ie63-1} raised from 0.124 h^-1 with sulfate and 0.150 h^-1 with nitrate to 0.193 h^-1 with nitrite as electron acceptor. Regardless of the electron acceptor in the culture medium, cell extracts exhibited absorption maxima corresponding to cytochromec and desulfoviridin. Nitrate reductase was found to be inducible by nitrate or nitrite, whereas nitrite reductase was synthesized constitutively. The activities of nitrate and nitrite reductases with hydrogen as electron donor were 0.2 and 0.3 mol/min·mg protein, respectively. If limiting amounts of hydrogen were added to culture bottles with nitrate as electron acceptor, part of the nitrate was only reduced to the level of nitrite. In media containing nitrate plus sulfate or nitrite plus sulfate, sulfate reduction was suppressed.The results demonstrate that the ammonification of nitrate or nitrite can function as sole energy conserving process in some sulfate-reducing bacteria.     

Transformation of the filamentous fungus Gibberella fujikuroi using the Aspergillus niger niaD gene encoding nitrate reductase

Summary A transformation system for Gibberella fujikuroi based on the Aspergillus niger nitrate reductase gene (niaD) was developed. A strain (designated SG140) carrying a non-reverting niaD mutation (niaD11) was generated by screening mutagenised cells for non-growth on nitrate as sole nitrogen source. Transformation frequencies of 1–2 transformants per g DNA were observed when strain SG140 was transformed to nitrate utilisation. Southern blot analyses of niaD⁺ transformants showed that the vector DNA sequences were integrated into the chromosomal DNA. The results demonstrate that the A. niger niaD gene is expressed in G. fujikuroi.     

Relationships between external nitrate availability,nitrate uptake and expression of nitrate reductase in roots of barley grown in N-limited split-root cultures

Despite the large number of studies of nitrate metabolism in plants, it remains undetermined to what extent this key plant system is controlled by overall plant N nutrition on the one hand, and by the nitrate ion itself on the other hand. To investigate these questions, V _max for nitrate uptake (high-affinity range), and nitrate reductase (NR) mRNA and activity, were measured in roots of N-limited barley (Hordeum vulgare L. cv. Golf) grown under conditions of constant relative addition of nitrate, with the seminal roots split between two culture compartments. The total amount of nitrate added per unit time (0.09·d^-1) was distributed between the two root parts (subroots) in ratios of 1000, 982, 955, 9010, 8020, and 5050. These nitrate-addition ratios resulted in nitrate fluxes ranging from 0 to 23 mol nitrate·g^-1 DW root·h^-1, while the external nitrate concentrations varied between 0 and 1.2 M. The apparent V _max for net nitrate uptake showed saturation-type responses to nitrate flux maintained during preceding growth. The flux resulting in half-maximal induction of nitrate uptake was approximately 4 mol nitrate·g^-1 DW root·h^-1, corresponding to an external nitrate concentration of 0.7 M. The activity of NR and levels of NR mRNA did not saturate within the range of nitrate fluxes studied. None of the parameters studied saturated with respect to the steady-state external nitrate concentration. At the zero nitrate addition — the 0%-root — initial uptake activity as determined in short-term ¹⁵N-labelling experiments was insignificant, and NR activity and NR mRNA were not detectable. However, nitrate uptake was rapidly induced, showing that the 0%-root had retained the capacity to respond to nitrate. These results suggest that local nitrate availability has a significant impact on the nitrate uptake and reducing systems of a split-root part when the total plant nitrate nutrition is held constant and limiting.Abbreviation NR nitrate reductase This work was supported by the Lars Hierta Memory Foundation, the Royal Swedish Academy of Sciences, and by the Swedish Natural Science Research Council via project grants (to C.-M.L. and B.I.) and visiting scientist grant (to W.H.C.). We thank Mrs. Ellen Campbell for technical advice, and Mrs. Judith V. Purves, Long Ashton Research Station, Long Ashton, UK, for analyses of ¹⁵N-labelling in tissue samples.     

Utilization of nitrate by bacteroids of Bradyrhizobium japonicum in the soybean root nodule

Bacteroids of Bradyrhizobium japonicum strain CB1809, unlike CC705, do not have a high level of constitutive nitrate reductase (NR; EC 1.7.99.4) in the soybean (Glycine max. Merr.) nodule. Ex planta both strains have a high activity of NR when cultured on 5 mM nitrate at 2% O₂ (v/v). Nitrite reductase (NiR) was active in cultured cells of bradyrhizobia, but activity with succinate as electron donor was not detected in freshly-isolated bacteroids. A low activity was measured with reduced methyl viologen. When bacteroids of CC705 were incubated with nitrate there was a rapid production of nitrite which resulted in repression of NR. Subsequently when NiR was induced, nitrite was utilized and NR activity recovered. Nitrate reductase was induced in bacteroids of strain CB1809 when they were incubated in-vitro with nitrate or nitrite. Increase in NR activity was prevented by rifampicin (10 g· ml^-1) or chloramphenicol (50 g·ml^-1). Nitrite-reductase activity in bacteroids of strain CB1809 was induced in parallel with NR. When nitrate was supplied to soybeans nodulated with strain CC705, nitrite was detected in nodule extracts prepared in aqueous media and it accumulated during storage (1°C) and on further incubation at 25°C. Nitrite was not detected in nodule extracts prepared in ethanol. Thus nitrite accumulation in nodule tissue appears to occur only after maceration and although bacteroids of some strains of B. japonicum have a high level of a constitutive NR, they do not appear to reduce nitrate in the nodule because this anion does not gain access to the bacteroid zone. Soybeans nodulated with strains CC705 and CB1809 were equally sensitive to nitrate inhibition of N₂ fixation.Abbreviations NR nitrate reductase - NiR nitrite reductase - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Changes in amino acid content of an algal feed species (Navicula sp.) and their effect on growth and survival of juvenile abalone (Haliotis rubra)

The growth and survival of juvenile Haliotis rubra, when fed with the diatom Navicula sp. cultured in f/2 medium containing combined nitrogen at 24.71 mg NO₃-N L^–1 (high), 12.35 mg NO₃-N L^–1 (standard) or 2.47 mg NO₃-N L^–1 (low), were compared in a 33-day trial. The alga in the low nitrogen medium contained 37% less total amino acid than that in the high and standard nitrogen media. There was a slightly greater reduction in essential amino acids (40%) compared to non-essential amino acids (35%). Juvenile abalone feeding on Navicula grown in medium with low nitrate and lower total amino acid content grew more slowly than when fed on the same species grown in standard or higher nitrogen medium with a higher amino acid content. The growth rate of juveniles was highest (43 m d^–1) in the high nitrate treatment followed (40 m d^–1) by the standard nitrate treatment and lowest (31 m d^–1) in the low nitrate treatment. The survival of the juveniles was also effected by the diet. Survival was better in the high and standard nitrogen media (88%) than the low nitrogen medium (75%). The results suggest that in order to achieve uniformity in nutritional quality of diatoms and good growth of abalone juveniles in commercial abalone nurseries, the nitrogen concentration in tanks should be monitored and additional nitrate added to provide an optimum concentration of between 2 and 12 mg NO₃-N L^–1.     

Genetic mapping by means of protoplast fusion in Bacillus subtilis

Summary A new mapping method involving protoplast fusion in Bacillus subtilis is described. Protoplasts from an isogenic standard marker strain containing purA and from a strain containing both purB and the marker, x, to be mapped were fused with polyethylene glycol, and purA ⁺ purB ⁺ fusants were selected. After isolation of single colonies and determination of unselected markers, marker x was mapped between two standard markers. This method was fully applicable to PBS1-resistant strains (e.g., lyt strains). The results obtained by protoplast fusion, conventional transformation and/or lysed protoplast transformation indicated that a lyt strain, Ni15, contained two new autolysin-minus mutations (lyt-151 and lyt-152). The properties of lyt-15 are also discussed.Abbreviations NTG N-methyl-N-nitro-N-nitrosoguanidine - SMM 0.5 M sucrose, 0.02 M MgCl₂, 0.02 M maleate buffer, pH 6.5     

Nitrate effects on the nodulation of legumes inoculated with nitrate-reductase-deficient mutants of Rhizobium

The effect of nitrate on the symbiotic properties of nitrate-reductase-deficient mutants of a strain of cowpea rhizobia (32H1), and of a strain of Rhizobium trifolii (TA1), were examined; the host species were Macroptilium atropurpureum (DC.) Urb. and Trifolium subterraneum L. Nitrate retarded initial nodulation by the mutant strains to an extent similar to that found with the parent strains. It is therefore unlikely that nitrite produced from nitrate by the rhizobia, plays a significant role in the inhibition of nodulation by nitrate. Nitrite is an inhibitor of nitrogenase, and its possible production in the nodule tissue by the action of nitrate reductase could be responsible for the observed inhibition of nitrogen fixation when nodulated plants are exposed to nitrate. However, the results of this investigation show that nitrogen fixation by the plants nodulated by parent or mutant strains was depressed by similar amounts in the presence of nitrate. No nitrite was detected in the nodules. Nodule growth, and to a lesser extent, the nitrogenase specific activity of the nodules (mol C₂H₄g^–1 nodule fr. wt. h^–1), were both affected by the added nitrate.     

The fate of 15N-labelled nitrate additions to a northern hardwood forest in eastern Maine,USA

We followed the movements of ¹⁵N-labelled nitrate additions into biomass and soil pools of experimental plots (15×15 m each) in a mid-successional beech-maple-birch-spruce forest in order to identify sinks for nitrate inputs to a forest ecosystem. Replicate plots (n=3) were spray-irrigated with either 28 or 56 kg N ha^–1 year^–1 using ¹⁵N-labelled nitric acid solutions (¹⁵N = 344 ) during four successive growing seasons (April–October). The ¹⁵N contents of foliage, bolewood, forests floor and mineral soil (0–5 cm) increased during the course of treatments. Mass balance calculations showed that one-fourth to one-third of the nitrate applied to forest plots was assimilated into and retained by above ground plant tissues and surface soil horizons at both rates of nitrate application. Plant and microbial assimilation were of approximately equal importance in retaining nitrate additions to this forest. Nitrate use among tree species varied, however, with red spruce showing lower rates of nitrate assimilation into foliage and bolewood than American beech and other deciduous species.     

The prime plasmalemma ATPase of the halophilic alga Dunaliella bioculata: purification and characterization

The prime plasmalemma ATPase of the halophilic green alga Dunaliella bioculata has been solubilized by Triton X-100 from a plasmalemma-rich membrane fraction and purified by anion-exchange chromatography. Vanadate-sensitive ATPase activity was totally enriched about 230-fold to a specific activity of approx. 250 nkat·mg protein^–1. The presence of Mg²⁺ or Mn²⁺ is essential for ATP hydrolysis by the enzyme. In addition to an equimolar requirement (11 Mg²⁺: ATP), there is further stimulation by Mg²⁺ (up to 20 mM) and by (100 mM) monovalent cations (K⁺ NH ₄ ⁺ >Rb⁺ -Na⁺ >Cs⁺ >Li⁺-choline⁺). Most anions have no or little effect. With a molecular mass of about 105 kDa for the single subunit, sensitivity to vanadate and N,N-dicyclohexylcarbodiimide (50% inhibition at about 1 M and 0.3 mM, respectively), strict ATP-specificity, and an acidic pH optimum, this enzyme shows the typical characteristics of the common type of H⁺-ATPase in the plasmalemma of higher plants and fungi. These results undermine the hypothesis of a wider distribution of a special (high salt) type of plasmalemma ATPase as found in the marine alga Acetabularia.Abbreviations BTP 1,3-bis[tris(hydroxymethyl)-methylamino]propane - DCCD N,N-dicyclohexylcarbodiimide - DES diethylstilbestrol - Mega-9 nonanoyl-N-methyl-glucamide - Mes N-morpholinoethanesulfonic acid - Mops N-morpholinopropanesulfonic acid - PAGE polyacrylamide-gel electrophoresis - PM plasmalemma-enriched membrane fraction - SDS sodium dodecyl sulfate This work was supported by the Deutsche Forschungsgemeinschaft; we thank Drs. M. Ikeda and D. Oesterhelt (MPI für Biochemie, Martinsried, FRG) for generous and valuable information about their work prior to publication.     

Rapid in vitro multiplication of jujube through mature stem explants

Stem explants obtained from a mature tree of Ziziphus mauritiana Lamk were grown on modified Murashige and Skoog medium containing 3800 mg l^-1 potassium nitrate, 2475 mg l^-1 ammonium nitrate, 11 M benzyladenine and 0.5 M indole-3-acetic acid. During successive subcultures 15–20 shoots per inoculum were produced. Rooting was induced by pretreatment with 50 M indolebutyric acid or 1-naphthaleneacetic acid for 24 h followed by transfer to auxin-free White's medium. Plantlets grew well in a soil and vermiculite mixture.Abbreviations IAA Indole-3-acetic acid - NAA 1-naphthaleneacetic acid - BA benzyladenine - MS Murashige and Skoog     

Increased taxane accumulation in callus cultures of Taxus cuspidata and Taxus × media by some elicitors and precursors

In Taxus cuspidata callus, vanadyl sulfate (10 mg l^–1) induced a high (146 g g^–1 dry wt) production of 10-deacetylbaccatin III in comparison to 7 g g^–1 dry wt of the control. The content of paclitaxel in this species increased from 16 g g^–1 to 74 g g^–1 dry wt when 20 mg phenylalanine l^–1 was used. In T. media, p-aminobenzoic acid induced the highest content of 10-deacetylbaccatin III (481 g g^–1 dry wt) versus 181 g g^–1 in the control. Paclitaxel increased from 89 to 139 g g^–1 dry wt after adding chitosan (20 mg l^–1) to the cultures.     

Effect of aluminium on yield and plant chemical concentrations of some temperate legumes

The aluminium (Al) tolerance of 34 temperate legume species (143 genotypes, including 57 from Trifolium repens) was determined in 60 experiments over a 3 year period in a low ionic strength (2.7 × 10^-3 M) solution culture. For each genotype, the relationship between solution Al³⁺ activity (M) and relative yield was determined and the Al³⁺ activity associated with a 50% reduction in yield (Al_RY50) calculated. In addition, plant chemical concentrations were determined in at least one genotype from most species. For white clover, Al_RY50 over all genotypes had an approximately normal distribution with mean of 1.31 M for the tops and 1.51 M for the roots, and a standard deviation of about 0.4. This suggested that Al tolerance had a polygenic inheritance. For the other species tested, Al_RY50 ranged from 0.15 to 4.53 M in the tops and from 0.21 to 4.89 M in the roots. In the tops and roots, 37% and 26% respectively of the genotypes had an Al_RY50 less than 1 M, including all species tested in the genera Melilotus and Medicago. Only 8% or 23% of the genotypes, based on the tops and roots respectively, had an Al_RY50 greater than 2, including all genotypes in the species Lotus pedunculatus. Except for Lotus, there were no consistent differences between genera in plant chemical concentrations. In Lotus, concentrations of Ca, Zn, Mn and Cu in the tops and of all elements except B in the roots were lower than that of the other species. The Al_RY50 of the species was not related to plant chemical concentrations in the absence of Al. Depending on the plant element, increasing solution Al concentrations had no significant effect on plant chemical concentrations for 56–94% of the species. When a significant effect did occur, increasing Al in solution generally decreased S and K concentrations and increased Mn, Zn, Cu Fe, B and Al concentrations in the tops and roots and decreased Ca concentrations in the tops. Plant P concentrations decreased in the tops but increased in the roots. Increasing Al in solution increase plant Al at the average rate of 44 g g^-1 M ^-1 (range 20–87) in the tops and 333 g M ^-1 (range 162–616) in the roots.     

Iron assimilation in plants: reduction of a ferriphytosiderophore by NADH:nitrate reductase from squash

NADH:nitrate reductase (EC 1.6.6.1) from squash (Cucurbita maxima Duch., cv. Buttercup) can catalyze the reduction of a ferriphytosiderophore from barley (Hordeum vulgare L. cv. Europa). Maximal activity occurs at pH 6, with an apparentK _m andV _max of 76 M and 21 nmol·min^-1·(mg protein)^-1, respectively. The ferriphytosiderophore strongly inhibits nitrate reduction catalyzed by nitrate reductase at the optimal pH for nitrate reduction, i.e. 7.5. On the contrary, nitrate is a poor inhibitor of ferriphytosiderophore reduction catalyzed by nitrate reductase at the optimal pH for this reaction, pH 6.0. Thus, squash has the potential to assimilate the iron from a ferriphytosiderophore synthesized by another plant.     

New Substrates for Enteropeptidase: I. Biologically Active Hepta-, Octa-, and Nonapeptides

Enteropeptidase (enterokinase, EC 3.4.21.9) hydrolyzes peptide bonds formed by carboxyl groups of Lys or Arg residue if less than four negatively charged amino acid residues are in positions P ₂–P ₅ of its substrate. We determined the kinetic parameters of three substrates of this type: human angiotensin II (AT) (DR VYIHPF) and the Hb(2–8) (LTAEEK A) and Hb(1–9) (MLTAEEK AA) peptides of the cattle hemoglobin -chain. The K _m values for all the substrates (10^–3 M) were one order of magnitude higher than those of the typical synthetic substrates of enteropeptidase or chimeric proteins with the –DDDDK– full-size linker (K _m 10^–4 M). The k _cat values for AT and Hb(2–8) were also close and low (30 min^–1). The general hydrolysis efficiency of such substrates is no more than 1% of the corresponding value for the typical peptide and protein substrates of the enteropeptidase. However, the elongation of Hb(2–8) peptide by one amino acid residue from both its N- and C-termini results in a dramatic increase in the catalytic efficiency of the hydrolysis: the k _cat value for Hb(1–9) is 1510 min^–1, which means that it is hydrolyzed only three times less effective than the chimeric protein with the full-size linker.     

Calcium acetate induces calcium uptake and formation of calcium-oxalate crystals in isolated leaflets of Gleditsia triacanthos L.

During treatment of isolated, peeled leaflets of Gleditsia triacanthos with 0.5–2 mM [⁴⁵Ca]acetate, saturation of the cell-wall free space with Ca²⁺ occurred within 10 min and was followed by a period of 6–10 h during which there was no significant Ca-uptake into the protoplast, but apoplastic Ca²⁺ was periodically released into the medium. Later, Ca²⁺ was absorbed for 3–4 d at rates of up to 2.2 mol Ca²⁺·h^-1·(g FW)^-1 to final concentrations of 350 mol Ca²⁺· (g FW)^-1. The distribution of absorbed Ca²⁺ between cell wall, vacuole and Ca-oxalate crystals was determined during Ca-uptake. Wheras intact, cut leaflets deposited absorbed Ca²⁺ as Ca-oxalate in the crystal cells, peeled leaflets lacking crystal cells accumulated at least 40–50 mol·(g FW)^-1 soluble Ca²⁺ before the absorbed Ca²⁺ was precipitated as Ca-oxalate. These observations indicate that the mechanisms for the continuous uptake of Ca²⁺, the synthesis of oxalate and the precipitation of Ca²⁺ as Ca-oxalate are operational in the crystal cells of intact leaflets, but not in the mesophyll cells of peeled leaflets where they must be induced by exposure to Ca²⁺. The precipitation of absorbed Ca²⁺ as Ca-oxalate by the crystal cells of isolated Gleditsia leaflets illustrates the role of these cells in the excretion of surplus Ca²⁺ which enters normal, attached leaves with the transpiration stream.In addition to acetate, only Ca-lactate and Ca-carbonate lead to Ca-uptake, but at rates well below those observed with Ca-acetate. Other small organic anions (citrate, glycolate, glyoxalate, malate) and inorganic anions (chloride, nitrate, sulfate) did not permit Ca-uptake. Acetate-¹⁴C was rapidly absorbed during Ca-uptake, but less than 20% was incorporated into Ca-oxalate; the rest remained mostly in the soluble fraction or was metabolized to CO₂. Acetate, as a permeable weak acid, may enable rapid Ca-uptake by stimulating proton extrusion at the plasmalemma and by serving as a counterion during Ca-accumulation in the vacuole, but is unlikely to function as the principal substrate for oxalate synthesis.     

Dynamics of the phycotoxin domoic acid: accumulation and excretion in two commercially important bivalves

Batch cultures of the toxigenic diatomNitzschia pungens Grunow f.multiseries Hasle were fed to blue mussels (Mytilus edulis) and deep sea Atlantic scallops (Placopecten magellanicus) to elucidate conditions under which domoic acid (DA) was accumulated and excreted (depurated). Mussels accumulated the toxin to a maximum level of 13 g g^-1, at rates of 0.21 to 3.7 g h^-1 g^-1, dry weight. Accumulation efficiency (the proportion of accumulated DA to estimated net uptake) ranged from 1–5%. The highest filtration rate of 1.71 h^-1 occurred at concentrations of 4–8 × 10⁶ Nitzschia cells 1^-1 with no formation of pseudofeces. Depuration rates between fed and starved mussels over a 2 h test period were the same. The depuration rate of domoic acid was about 17% d^-1 and did not account for the low uptake efficiencies, so it is suggested that most of the DA is lost from mussels in the solution during the feeding process. Domoic acid accumulation in mussels was dependent on the amount of toxin available, which in turn was a function of the density and growth phase of theNitzschia population. Changes in filtration rate withNitzschia concentration and depuration rate with time can account for the DA levels of mussels collected during toxic episodes in Cardigan Bay, Prince Edward Island, Canada in 1988 and 1989.Scallops accumulated DA (0.39–1.3 g h^-1 g^-1, more slowly than mussels, however, accumulation efficiencies ranged from 5–100%. Filtration rates remained relatively low and constant at 0.081 h^-1. Scallops retained domoic acid longer than mussels, a fact which must be considered in the marketing of whole scallops for human consumption.     

Arsenic concentrations in water and fish from Chautauqua Lake,New York

Synopsis Arsenic persists in Chautauqua Lake, New York waters 13 years after cessation of herbicide (sodium arsenite) application and continues to cycle within the lake. Arsenic concentrations in lake water ranged from 22.4–114.81 g l^–1, = 49.0 ag l^–1. Well water samples generally contained less than 10 g l^–1 arsenic. Arsenic concentrations in lake water exceeded U.S. Public Health Service recommended maximum concentrations (10 g l^–1) and many samples exceeded the maximum permissible limit (50 g l^–1). Fish accumulated arsenic from water but did not magnify it. Fish to water arsenic ratios ranged from 0.4–41.6. Black crappie (Pomoxis nigromaculatus) contained the highest arsenic concentrations (0.14–2.04 g g^–1 ), X = 0.7 g g^–1) while perch (Perca flavescens), muskellunge (Esox masquinongy) and largemouth bass (Micropterus salmoides) contained the lowest concentrations (0.02–0.13 g g^–1). Arsenic concentrations in fish do not appear to pose a health hazard for human consumers.     

The phytoplankton of Lake Liddell,New South Wales: chlorophyll a concentrations,species seasonal succession,and covariation with nutrients

Samples of the phytoplankton in a freshwater lake, Lake Liddell, New South Wales (Lat: 32° 22 S, Long. 150° 1 E) were collected every 4 weeks between October 1987 and November 1988. Chlorophyll a concentrations ranged from 1.8 g 1^–1 to 9.1 g 1^–1 and were positively correlated with the following nutrient parameters: total and nett mass additions of nitrate/nitrite-N and total-N, total additions of Kjeldahl-N, and nett mass addition N-P ratios. There was no correlation between lake nutrient concentrations and chlorophyll a. Factors other than nutrient concentrations appeared to be effecting chlorophyll a concentrations as summer levels were low despite nutrient concentrations being at a maximum. In spring and summer the phytoplankton was dominated by chlorophytes, with dinoflagellates and diatoms most abundant in autumn. During winter cyanobacteria were the most abundant. The relative abundance of chlorophytes was positively correlated with in lake nitrate/nitrite-N concentrations whereas the relative abundance of cyanobacteria was negatively correlated with this parameter. Based on chlorophyll a concentrations and the phytoplankton flora Lake Liddell can be classified as mesotrophic.