Nutrient removal by thermophilic Fischerella (Mastigocladus laminosus) in a simulated algaculture process

A novel nutrient removal/waste heat utilization process was simulated using semicontinuous cultures of the thermophilic cyanobacterium Fischerella. Dissolved inorganic carbon (DIC)-enriched cultures, maintained with 10 mg l⁻¹ daily productivity, diurnally varying temperature (from 55°C to 26–28°C), a 12:12 light cycle (200 μE sec⁻¹ m⁻²) and 50% biomass recycling into heated effluent at the beginning of each light period, removed > 95% of NO₃⁻ + NO₂⁻−N, 71% of NH₃-N, 82% of PO₄³⁻ −P, and 70% of total P from effluent water samples containing approximately 400 μg l⁻¹ combined N and 60 μg l⁻¹ P. Nutrient removal was not severely impaired by an altered temperature gradient, doubled light intensity, or DIC limitation. Recycling 75% of the biomass at the end of each light period resulted in unimpaired NO₃⁻ + NO₂⁻ removal, 38–45% P removal and no net NH₃ removal. Diurnally varying P removal, averaging 50–60%, and nearly constant > 80% N removal, are therefore projected for a full-scale process with continuous biomass recycling.     

Perchlorate and nitrate reductase activity in the perchlorate-respiring bacterium perclace

The perchlorate (ClO₄⁻)-respiring organism, strain perc1ace, can grow using nitrate (NO₃⁻) as a terminal electron acceptor. In resting cell suspensions, NO₃⁻ grown cells reduced ClO₄⁻, and ClO₄⁻ grown cells reduced NO₃⁻. Activity assays showed that nitrate reductase (NR) activity was 1.31 μmol min⁻¹ (mg protein)⁻¹ in ClO₄⁻ grown cells, and perchlorate reductase (PR) activity was 4.24 μmol min⁻¹ (mg protein)⁻¹ in NO₃⁻ grown cells. PR activity was detected within the periplasmic space, with activities as high as 14 μmol min⁻¹ (mg protein)⁻¹. The NR had a pH optimum of 9.0 while the PR had an optimum of 8.0. This study suggests that separate terminal reductases are present in strain perclace to reduce NO₃⁻ and ClO₄⁻.     

Nitrite effect on nitrous oxide emission from denitrifying activated sludge

Laboratory-scale experiments were conducted to examine the N₂O emission during the denitrification process. For each of the 6 runs carried out, synthetic effluent was fed in a 10 l batch mixed liquor to investigate the effect of nitrite on N₂O emission and Helium was continuously bubbled through the reactor at constant rate (0.12 l/min) to favour N₂O transfer and detection. An increasing COD/NO₃⁻-N influent ratio from 3 to 7 was firstly applied (runs 1–3). Secondly, NO₂⁻ pulse additions were performed during run 4 and 5 (10 and 20 mg N/l, respectively). Finally, the reactor was fed with influent containing both NO₂⁻ and NO₃⁻. We showed that N₂O emission was detected shortly after NO₂⁻ accumulation, few minutes after the substrate feeding. The highest emission occurred at the lower COD/NO₃⁻-N ratio (=3) and at the higher NO₂⁻ addition (20 mg N/l). In addition, the higher nitrogen conversion to N₂O gas (14.4%) was obtained with an influent containing initially both NO₂⁻ and NO₃⁻. Our results suggest a direct effect of the NO₂⁻ concentration on the N₂O emission. We have also confirmed the inhibitory effect of NO₂⁻ concentration on N₂O reduction.     

Kinetics of the reactions of nitrogen dioxide with glutathione,cysteine, and uric acid at physiological pH

Nitrogen dioxide (NO₂^•) is a key biological oxidant. It can be derived from peroxynitrite via the interaction of nitric oxide with superoxide, from nitrite with peroxidases, or from autoxidation of nitric oxide. In this study, submicromolar concentrations of NO₂^• were generated in < 1 μs using pulse radiolysis, and the kinetics of scavenging NO₂^• by glutathione, cysteine, or uric acid were monitored by spectrophotometry. The formation of the urate radical was observed directly, while the production of the oxidizing radical obtained on reaction of NO₂^• with the thiols (the thiyl radical) was monitored via oxidation of 2,2′-azino-bis-(3-ethylthiazoline-6-sulfonic acid). At pH 7.4, rate constants for reaction of NO₂^• with glutathione, cysteine, and urate were estimated as 2 × 10⁷, 5 × 10⁷, and 2 × 10⁷ M⁻¹ s⁻¹, respectively. The variation of these rate constants with pH indicated that thiolate reacted much faster than undissociated thiol. The dissociation of urate also accelerated reaction with NO₂^• at pH > 8. The thiyl radical from GSH reacted with urate with a rate constant of 3 × 10⁷ M⁻¹ s⁻¹. The implications of these values are: (i) the lifetime of NO₂^• in cytosol is < 10 μs; (ii) thiols are the dominant ‘sink’ for NO₂^• in cells/tissue, whereas urate is also a major scavenger in plasma; (iii) the diffusion distance of NO₂^• is 0.2 μm in the cytoplasm and < 0.8 μm in plasma; (iv) urate protects GSH against depletion on oxidative challenge from NO₂^•; and (v) reactions between NO₂^• and thiols/urate severely limit the likelihood of reaction of NO₂^• with NO• to form N₂O₃ in the cytoplasm.     

A study in UF-membrane reactor on activity and stability of nitrile hydratase from Microbacterium imperiale CBS 498-74 resting cells for propionamide production

The bioconversion of propionitrile to propionamide was catalysed by nitrile hydratase (NHase) using resting cells of Microbacterium imperiale CBS 498-74 (formerly, Brevibacterium imperiale). This microorganism, cultivated in a shake flask, at 28 °C, presented a specific NHase activity of 34.4 U mg_DCW⁻¹ (dry cell weight). The kinetic parameters, K_m and V_max, tested in 50 mM sodium phosphate buffer, pH 7.0, in the propionitrile bioconversion was evaluated in batch reactor at 10 °C and resulted 21.6 mM and 11.04 μmol min⁻¹ mg_DCW⁻¹, respectively. The measured apparent activation energy, 25.54 kJ mol⁻¹, indicated a partial control by mass transport, more likely through the cell wall.

UF-membrane reactors were used for kinetic characterisation of the NHase catalysed reaction. The time dependence of enzyme deactivation on reaction temperature (from 5 to 25 °C), on substrate concentrations (from 100 to 800 mM), and on resting cell loading (from 1.5 to 200 μg  ml⁻¹) indicated: lower diffusional control (E_a=37.73 kJ mol⁻¹); and NHase irreversible damage caused by high substrate concentration. Finally, it is noteworthy that in an integral reactor continuously operating for 30 h, at 10 °C, 100% conversion of propionitrile (200 mM) was attained using 200 μg  ml⁻¹ of resting cells, with a maximum volumetric productivity of 0.5 g l⁻¹ h⁻¹.     

Nitrogen mineralisation and plant nitrogen acquisition in a nitrogen-limited calcareous grassland

A field study measured the rate of soil mineral N supply and its effects on plant biomass and N accumulation in a 13-year-old, naturally regenerating, calcareous grassland. Gross rates of N mineralisation (2 μg g⁻¹ day⁻¹, i.e. 0.69 kg ha⁻¹ day⁻¹), assessed using ¹⁵N pool dilution, were at the lower end of the range previously reported for grasslands. Weekly additions of liquid N fertiliser ([NH₄]₂SO₄, NH₄NO₃ or KNO₃) and, to a lesser extent the addition of water, increased plant growth substantially, demonstrating that the primary constraint to plant growth was low N availability. In plants that had received NO₃⁻, the activity of the inducible enzyme nitrate reductase in shoots initially increased in proportion to the amount of NO₃⁻ supplied. However, as above-ground herbage accumulated, nitrate reductase activity declined to similar low levels in all treatments, despite the continuance of the constant NO₃⁻ additions. The decline in NR specific activity reflected declining tissue NO₃⁻ concentrations, although total plant NRA may have remained constant during the period of study. The study has shown that plant growth is limited by low N mineralisation rates and indeed the soil is a sink for much added N. Low water availability provides an additional constraint on N mineralisation in this calcareous grassland soil. Any disturbances in the N cycle which increase the availability of mineral N will result in a substantial increase in plant growth within this ecosystem.     

A nitrite reductase with cytochrome oxidase activity from Micrococcus denitrificans

The formation of nitrite reductase and cytochrome c in Micrococcus denitrificans was repressed by O₂. The purified nitrite reductase utilized reduced forms of cytochrome c, phenazine methosulphate, benzyl viologen and methyl viologen, respectively, as electron donors. The enzyme was inhibited by KCN, NaN₃ and NH₂OH each at 1 mM, whereas CO and bathocuproin, diethyl dithiocarbamate, o-phenanthroline and ,'-dipyridyl at 1 mM concentrations were relatively ineffective. The purified enzyme contains cytochromes, probably of the c and a₂ types, in one complex. A K_m of 46 μM for NO₂⁻ and a pH optimum of 6.7 were recorded for the enzyme. The molecular weight of the enzyme was estimated to be around 130000, and its anodic mobility was 6.8·10⁻⁶ cm²·sec⁻¹·V⁻¹ at pH 4.55.

The most highly purified nitrite reductase still exhibited cytochrome c oxidase activity with a K_m of 27 μM for O₂. This activity was also inhibited by KCN, NaN₃ and NH₂OH and by NO₂⁻.

A constitutive cytochrome oxidase associated with membranes was also isolated from cells grown anaerobically with NO₂⁻. It was inhibited by smaller amounts of KCN, NaN₃ and NH₂OH than the cytochrome oxidase activity of the nitrite reductase enzyme and also differed in having a pH optimum of about 8 and a K_m for O₂ of less than 0.1 μM. Spectroscopically, cytochromes b and c were found to be associated with the constitutive oxidase in the particulate preparation. Its activity was also inhibited by NO₂⁻.

The physiological role of the cytochrome oxidase activity associated with the purified nitrite reductase is likely to be of secondary importance for the following reasons: (a) it accounts for less than 10% of total cytochrome c oxidase activity of cell extracts; (b) the constitutive cytochrome c oxidase has a smaller K_m for O₂ and would therefore be expected to function more efficiently especially at low concentrations of O₂.     

Elemental composition and food intake of Phialidium hydromedusae in the laboratory

Elemental composition and feeding rate of hydromedusae Phialidium sp. on copepods were studied in the laboratory. Regression equations for both mature and immature medusae allowed the estimation of their dry weight (DW), total C and N content as a function of their diameter. The mean C content as percentage of the DW varied from 13.13% ( ) for the immature to 19.38% (5.68) for the mature individuals. The mean N content is 4.03% (2.49) of DW of immatures and 5.85% (2.70) of the matures. Ingestion rate of Phialidium sp. fed on copepods (200–500 μm) increased with prey density but reached a maximum at high prey concentrations. A maximum ingestion rate of 8.55 (1.6) copepods · medusa ⁻¹ · h⁻¹ was reached for prey concentrations of > 140 copepods · 1 ⁻¹ for both immature and mature medusae. Maximum daily consumption of prey weight varied from 1.41 to 978% C body weight for mature medusae and from 2.90 to 975% for the immature individuals.     

Bipyridylium quaternary salts and related compounds. V. Pulse radiolysis studies of the reaction of paraquat radical with oxygen. Implications for the mode of action of bipyridyl herbicides

1. Rate constants for reduction of paraquat ion (1,1′-dimethyl-4,4′-bipyridy-lium, PQ²⁺) to paraquat radical (PQ⁺·) by e⁻_aq and CO₂⁻· have been measured by pulse radiolysis. Reduction by e⁻_aq is diffusion controlled (k = 8.4·10¹⁰ M⁻¹·s⁻¹) and reduction by CO₂⁻· is also very fast k = 1.5·10¹⁰ M⁻¹·s⁻¹).

2. The reaction of paraquat radical with oxygen has been analysed to give rate constants of 7.7·10⁸ M⁻¹·s⁻¹ and 6.5·10⁸ M⁻¹·s⁻¹ for the reactions of paraquat radical with O₂ and O₂⁻·, respectively. The similarity in these rate constants is in marked contrast to the difference in redox potentials of O₂ and O₂⁻· (− 0.59 V and + 1.12 V, respectively).

3. These rate constants, together with that for the self-reaction of O₂⁻·, have been used to calculate the steady-state concentration of O₂⁻· under conditions thought to apply at the site of reduction of paraquat in the plant cell. On the basis of these calculations the decay of O₂⁻· appears to be governed almost entirely by its self-reaction, and the concentration 5 μm away from the thylakoid is still 90% of that at the thylakoid itself. Thus, O₂⁻· persists long enough to diffuse as far as the chloroplast envelope and tonoplast, which are the first structures to be damaged by paraquat treatment. O₂⁻· is therefore sufficiently long-lived to be a candidate for the phytotoxic product formed by paraquat in plants.     

Growth and photosynthesis of Hydrocotyle ranunculoides L. fil. in Central Europe

Floating Pennywort (Hydrocotyle ranunculoides L. fil.) is a worldwide distributed aquatic plant. The species is native to North America and quite common also in Central and South America. In Europe, Japan and Australia it is known as an alien plant, sometimes causing serious problems for affected ecosystems and human use of water bodies. Starting from Western Europe with an eastwards directed spread, Floating Pennywort was recorded in Germany in 2004 for the first time. Since then, the species spread out and got established in western parts of Central Europe. For a definite prediction of the potential of a further spread, data about biology, in particular growth and photosynthesis are needed. Here, regeneration capacity, growth at different nutrient availabilities and photosynthesis of H. ranunculoides were investigated. In addition biomass samples were taken in the field. Results show an enormous regeneration capacity (e.g., by forming new shoots from small shoot fragments), increasing growth rates under increasing nutrient availability and a maximum increase of biomass reaching 0.132±0.008 g g⁻¹ dw d⁻¹. Dense populations of H. ranunculoides growing in ponds and oxbows were found at high nutrient content of the substrate, the biomass reaching there up to 532.4±14.2 g dw m⁻². Gas exchange analysis showed a physiological optimum of H. ranunculoides CO₂ uptake at temperatures between 25 and 35 °C and high photon flux densities (PPFD) above 800 μmol photons m⁻² s⁻¹. In comparison, native Hydrocotyle vulgaris showed an optimum of net photosynthesis at 20–30 °C and a light saturation of CO₂ gas exchange at 350 μmol photons m⁻² s⁻¹.     

Oxidative phosphorylation coupled to oxygen uptake and nitrate reduction in Micrococcus denitrificans

A procedure is described for preparing particles from cells of Micrococcus denitrificans which were broken osmotically after treatment with lysozyme.

1. 1. The preparations catalysed ATP synthesis coupled to O₂ uptake or NO₃⁻ reduction. With NADH or succinate as the electron donors the P:O ratios were about 1.5 and 0.5, respectively; and the P:NO₃⁻ ratios were about 0.9 and 0.06, respectively.

2. 2. Addition of ADP or P_i to the reaction mixture increased the rates of NADH-dependent O₂ uptake and NO₃⁻ reduction. Addition of 1 mM 2,4-dinitrophenol, which inhibited phosphorylation by 50–60%, increased the basal rates of electron transport.

3. 3. Evidence derived from spectrophotometry and from the differential inhibition by antimycin A of O₂ and NO₃⁻ reduction leads to the conclusion that the nitrate reductase interacted with the respiratory chain in the region of the b-type cytochrome, and that the c-type cytochrome present was not involved in the reduction of NO₃⁻ to NO₂⁻.

Characterization of the particulate nitrite oxidase and its component activities from the chemoautotroph Nitrobacter agilis

1. Difference spectra, at room and liquid N₂ temperatures, of S₂O₄²⁻-, and NO₂⁻-reduced intact cells and cell-free preparations of Nitrobacter agilis demonstrated the presence of cytochromes of the c- and a-types. Reduction of cytochromes by succinate, and to a limited extent, by NADPH also occurred, provided KCN (0.1 mM) was also present.

2. A particulate, heat-labile nitrite oxidase having an absolute requirement for O₂ was prepared from N. agilis cells using sonic oscillation and differential centrifugation. The particles also possessed NADH oxidase, succinoxidase, formate oxidase and traces of NADPH oxidase activity. The stoichiometry of the nitrite oxidase reaction approached the theoretical value of 2 moles of NO₂⁻ consumed per mole of O₂ consumed. The pH optimum of the nitrite oxidase system shifted to progressively more alkaline values as the NO₂⁻ concentration was increased, changing from a pH value of 6.8 at 0.6 mM KNO₂ to pH 8.0 at 0.01 M KNO₂ with apparent K_m's of 0.2 and 1.2 mM NO₂⁻, respectively. Computations of the HNO₂ concentrations present under the above conditions showed an approx. 500-fold greater affinity for HNO₂ which was independent of pH, suggesting the involvement of HNO₂ as both a substrate and an inhibitor (at higher concentrations) of the nitrite oxidase system. The marked inhibition by NaN₃, NaCN and Na₂S, as well the light-reversible inhibition by CO, indicated the presence of cytochrome oxidase which was subsequently characterized. NO₂⁻ proved to be a competitive inhibitor of the nitrite oxidase system.

3. The particulate preparation also possessed a heat-labile nitrite-cytochrome c reductase activity which was energy independent and routinely measured under anaerobic conditions. As in the case of nitrite oxidase, the affinity of the enzyme for NO₃⁻ increased as the pH was lowered, but the pH optimum remained unaffected. In terms of calculated HNO₂ concentration an approximately constant K_m of about 0.2 μM was estimated at the several pH's examined. The inhibition by NO₃⁻ was shown to be competitive. The marked sensitivity of the reductase to several metal-binding agents implicated a metal component in the electron transport chain at the site prior to cytochrome c.

4. The membrane-like composition of the nitrite oxidase system is indicated.     

Photosynthetic photon flux effects on bean response to nitrogen dioxide

Phaseolus vulgaris L. cv. Kinghorn Wax seedlings, supplied with nutrient solution containing either 0 or 5 mM nitrate as sole N source, were exposed to 0.25 μl/l NO₂ for 6 hr each day for 10 days at continuous photosynthetic photon flux (PPF) of 100, 300, 500 or 700 μmol m⁻² sec⁻¹. There was a significant interaction of PPF and nitrate. Shoot and root dry weights increased with increasing PPFs only when nitrate was supplied. The main effects of NO₂ on plant growth were significant; none of the interactions involving NO₂ were significant. Exposure to NO₂ decreased shoot and root dry weight in both the presence and absence of nutrient N and at all PPF levels. All interactions were significant for in vitro leaf nitrate reductase activity (NRA), which increased markedly at PPFs above 100 μmol m⁻² sec⁻¹ when nitrate was supplied. Treatment with NO₂ strongly inhibited enzyme activity in the presence of nitrate, particularly at the 300 μmol m⁻² sec⁻¹ PPF level. These experiments demonstrated that PPF level does not modify the effect of NO₂ on growth but does have a major effect on NRA and on NO₂ effects on NRA in the presence of nutrient nitrate.     

Photosynthetic response of Myriophyllum salsugineum A.E. orchard to photon irradiance, temperature and external free CO2

The photosynthetic capacity of Myriophyllum salsugineum A.E. Orchard was measured, using plants collected from Lake Wendouree, Ballarat, Victoria and grown subsequently in a glasshouse pond at Griffith, New South Wales. At pH 7.00, under conditions of constant total alkalinity of 1.0 meq dm⁻³ and saturating photon irradiance, the temperature optimum was found to be 30–35°C with rates of 140 μmol mg⁻¹ chlorophyll a h⁻¹ for oxygen production and 149 μmol mg⁻¹ chlorophyll a h⁻¹ for consumption of CO₂. These rates are generally higher than those measured by other workers for the noxious Eurasian water milfoil, Myriophyllum spicatum L., of which Myriophyllum salsugineum is a close relative. The light-compensation point and the photon irradiance required to saturate photosynthetic oxygen production were exponentially dependent on water temperature. Over the temperature range 15–35°C the light-compensation point increased from 2.4 to 16.9 μmol (PAR) m⁻² s⁻¹ for oxygen production while saturation photon irradiance increased from 41.5 to 138 μmol (PAR) m⁻² s⁻¹ for oxygen production and from 42.0 to 174 μmol (PAR) m⁻² s⁻¹ for CO₂ consumption. Respiration rates increased from 27.1 to 112.3 μmol (oxygen consumed) g⁻¹ dry weight h⁻¹ as temperature was increased from 15 to 35°C. The optimum temperature for productivity is 30°C.     

Influence of phosphorus concentration on the growth kinetics and stoichiometry of the microalga Scenedesmus obliquus

The growth of the freshwater microalga Scenedesmus obliquus was studied at 30°C in a mineral culture medium with phosphorus concentrations of between 0 and 372 μ . The values for the specific growth rates, between and , fitted a semistructured substrate-limitation model with μ_m1 = 0·0466 h⁻¹, μ_m2 = 0·0256 h⁻¹ and . The specific uptake rate of phosphorus reached a maximum value of q_Sm1 = 658·01 × 10⁻⁴ μmol P mg⁻¹ biomass h⁻¹.     

The reaction between the superoxide anion radical and cytochrome c

1. 1. The superoxide anion radical (O₂⁻) reacts with ferricytochrome c to form ferrocytochrome c. No intermediate complexes are observable. No reaction could be detected between O₂⁻ and ferrocytochrome c.

2. 2. At 20 °C the rate constant for the reaction at pH 4.7 to 6.7 is 1.4 · 10⁶ M⁻¹ · s⁻¹ and as the pH increases above 6.7 the rate constant steadily decreases. The dependence on pH is the same for tuna heart and horse heart cytochrome c. No reaction could be demonstrated between O₂⁻ and the form of cytochrome c which exists above pH ≈ 9.2. The dependence of the rate constant on pH can be explained if cytochrome c has pKs of 7.45 and 9.2, and O₂⁻ reacts with the form present below pH 7.45 with k = 1.4 · 10⁶ M⁻¹ · s⁻¹, the form above pH 7.45 with k = 3.0 · 10⁵ M⁻¹ · s⁻¹, and the form present above pH 9.2 with k = 0.

3. 3. The reaction has an activation energy of 20 kJ mol⁻¹ and an enthalpy of activation at 25 °C of 18 kJ mol⁻¹ both above and below pH 7.45. It is suggested that O₂⁻ may reduce cytochrome c through a track composed of aromatic amino acids, and that little protein rearrangement is required for the formation of the activated complex.

4. 4. No reduction of ferricytochrome c by HO₂ radicals could be demonstrated at pH 1.2–6.2 but at pH 5.3, HO₂ radicals oxidize ferrocytochrome c with a rate constant of about 5 · 10⁵–5 · 10⁶ M⁻¹ · s⁻¹

.     

Crystal and microparticle effects on MDCK cell superoxide production: oxalate-specific mitochondrial membrane potential changes

We have previously shown that crystals of calcium oxalate (COM) elicit a superoxide (O₂⁻) response from mitochondria. We have now investigated: (i) if other microparticles can elicit the same response, (ii) if processing of crystals is involved, and (iii) at what level of mitochondrial function oxalate acts. O₂⁻ was measured in digitonin-permeabilized MDCK cells by lucigenin (10 μM) chemiluminescence. [¹⁴C]-COM dissociation was examined with or without EDTA and employing alternative chelators. Whereas mitochondrial O₂⁻ in COM-treated cells was three- to fourfold enhanced compared to controls, other particulates (uric acid, zymosan, and latex beads) either did not increase O₂⁻ or were much less effective (hydroxyapatite +50%, p < 0.01), with all at 28 μg/cm². Free oxalate (750 μM), at the level released from COM with EDTA (1 mM), increased O₂⁻ (+50%, p < 0.01). Omitting EDTA abrogated this signal, which was restored completely by EGTA and partially by ascorbate, but not by desferrioxamine or citrate. Omission of phosphate abrogated O₂⁻, implicating phosphate-dependent mitochondrial dicarboxylate transport. COM caused a time-related increase in the mitochondrial membrane potential (Δψ_m) measured using TMRM fluorescence and confocal microscopy. Application of COM to Fura 2-loaded cells induced rapid, large-amplitude cytosolic Ca²⁺ transients, which were inhibited by thapsigargin, indicating that COM induces release of Ca²⁺ from internal stores. Thus, COM-induced mitochondrial O₂⁻ requires the release of free oxalate and contributes to a synergistic response. Intracellular dissociation of COM and the mitochondrial dicarboxylate transporter are important in O₂⁻ production, which is probably regulated by Δψ_m.     

Halophila ovalis (R. Br.) Hook. f. from a submarine hot spring in southern Japan

Colonies of the seagrass Halophila ovalis are found growing adjacent to coral Acropora sp. and Seriatopora hystrix in a submarine hot spring (at 15.7 m depth, 28.6°C) at the north coast of Taketomi Island, near the southern tip of Japan. Halophila plants grow in sea water containing sulphide 930 μg S ml⁻¹ and on the substratum with fine precipitates of the submarine hot spring which have sulphide content up to 5400 μg S g⁻¹ DW. The accumulated sulphide concentration reaches as high as 8400 μg S g⁻¹ DW in under ground tissues and 5700 μg S g⁻¹ DW in above-ground tissues, respectively. It is suggested that, not the sulphide concentration but light and possibly water temperature are the limiting factors for the Halophila colonization in the submarine hot spring.     

Effects of food nitrogen content and concentration on the forms of nitrogen excreted by the calanoid copepod, Acartia tonsa

Nitrogen excreted as ammonium, urea, and dissolved primary amines (DPA), and nitrogen ingested by the planktonic calanoid copepod, Acartia tonsa, were measured while fed 4 foods with different N/C ratios in high (500 μg C l^− 1) and low (50 μg C l^− 1) concentrations. Adult copepods were fed the ciliate, Uronema marinum (N/C = 0.26), the diatom, Thalassiosira weissflogii, in log-phase growth (N/C = 0.20), and in senescent-phase growth (N/C = 0.12), and detritus derived from the saltmarsh grass, Spartina alterniflora, (N/C = 0.04). Total nitrogen excreted ranged from 0.06 to 0.18 μg N copepod^− 1 d^− 1 whereas nitrogen ingested exhibited considerably more variation (0.01 to 0.39 μg N copepod ^− 1d ^− 1). Ammonium was the dominant form of nitrogen excreted and was influenced by both food concentration and N/C ratio. Copepods fed foods with N/C ratios resembling their own body composition (log-phase diatoms and ciliates) excreted more ammonium when fed higher concentrations of food. In contrast, copepods fed foods with lower N/C ratios than their own body composition excreted more ammonium when fed lower concentrations of food, suggesting that they were catabolizing body protein for survival. Excretion of urea varied with food N/C ratio, with more urea excreted when the copepods were fed higher N/C foods. The excretion of DPA did not vary with either food concentration or food N/C ratio. Homeostasis serves to conserve the N/C ratio of copepods. Thus nitrogen excretion by healthy copepods should be expected to increase with ingestion only when copepods have high quantities of nitrogen-rich foods relative to the body composition of the copepods.     

Metal accumulation by Halodule wrightii populations

Metal concentrations and population parameters of the seagrass Halodule wrightii were determined at three locations at Rio de Janeiro State, Brazil. The possible increase of metal availability in one of these areas, Sepetiba Bay, as a result of dredging of contaminated bottom sediments which ocurred, was evaluated by analyses of Al, Cd, Cr, Cu, Fe, Ni, Pb and Zn in root, rhizome and shoots. In addition, analyses were carried out in H. wrightii populations from non-contaminated areas located at northwestern (Cabo Frio) and southeastern (Angra do Reis) regions of Rio de Janeiro State. Concurrently, abundance and density data of the seagrass populations were obtained. It was found that concentration from Sepetiba Bay samples up to 1.6 ± 0.4 μg g⁻¹ of Cd, 12 ± 1.0 μg g⁻¹ of Cr, 27 ± 2.4 μg g⁻¹ of Pb, 291 ± 47 μg g⁻¹ of Mn, 128 ± 23 μg g⁻¹ of Zn were significantly higher than that from two other collection sites. An increase in Cd and Zn concentration was observed in H. wrightii from Sepetiba Bay indicating that metal mobilization from contaminated sediments through dredging activities were, at least in part, transferred to the biotic compartment via accumulation by the seagrass. The populations of seagrass within the region demonstrated quite substantial changes in biomass data but not in shoot or rhizome density during the study. Such changes in biomass are to be expected, as these dynamics are typical of the small, isolated monospecific populations of H. wrightii along the Rio de Janeiro coast.