Zooplankton responses to predation by larval bluegill: an enclosure experiment

SUMMARY 1. Larval fish are gape-limited predators that forage on prey of specific sizes, and thus may be expected to differentially affect members of a zooplankton community, possibly altering the size-structure or species composition.
2. I used an enclosure experiment to look at the effect of predation by larval bluegill on the dynamics of two zooplankton communities, one dominated by large-bodied individuals and the other by small-bodied individuals. Enclosures containing these zooplankton received a zero, low, medium, or high density of larval bluegill predators.
3. Increasing larval density had a negative effect on zooplankton abundance and abundance declined similarly in the large-bodied and small-bodied communities.
4. Zooplankton size-structure, as estimated by the length of the average zooplankton, increased and then decreased during the experiment, decreasing faster at higher larval fish densities. When zooplankton size-structure was estimated as the length of the average cladoceran, size-structure declined in the large-bodied but not in the small-bodied community and the greatest decline in size-structure was seen in the medium and high larval density treatments.
5. Ordination of each community using multidimensional scaling (MDS) indicated that the trajectory of change in species composition differed between the presence and absence of larval fish. In both communities, the degree of response by individual taxa depended on the density of bluegill larvae. This effect on zooplankton abundance, size-structure and community composition suggests that larval fish may make an important contribution to zooplankton dynamics in many lakes and ponds.     

Eutrophication and its control by biomanipulation: an enclosure experiment

Biomanipulation experiments were carried out in small enclosures in a small, shallow eutrophic lake in eastern England. The effects of fish removal on water quality and planktonic communities were examined in relation to nutrients and macrophytes. Exclusion of fish resulted in enhanced densities of the large-bodied Daphnia hyalina which, in turn, led to improvements in water quality. The provision of refuges from fish predation also enhanced Daphnia populations enough to suggest this strategy as feasible for the restoration of this lake. The development of a mysid population in enclosures without fish indicated that some indirect effects might occur if fish are completely removed.     

Roles of phosphate and an enoyl radical in ferritin iron mobilization by 5-aminolevulinic acid

5-Aminolevulinic acid (ALA), a heme precursor that accumulates in acute intermittent porphyria (AIP) and lead poisoning, undergoes enolization and subsequent iron-catalyzed oxidation at neutral pH. Iron is released from horse spleen ferritin (HoSF) by both ALA-generated O₂^•− and enoyl radical (ALA√), which amplifies the chain of ALA oxidation (autocatalysis). Iron chelators such as EDTA, ATP, but not citrate, and phosphate accelerate this process and ALA-promoted iron release from HoSF is faster in horse spleen isoferritins containing larger amounts of phosphate in the core. ALA (+0.377 V versus standard hydrogen electrode) is less effective in releasing iron from ferritin than are thioglycollic acid, 6-hydroxydopamine, and N,N,N′,N′-tetramethyl-p-phenylenediamine. During electrochemical one electron oxidation of ALA in a nitrogen atmosphere, spin trapping experiments with 3,5-dibromo-4-nitrosobenzenesulfonic acid demonstrated the formation of a spin adduct characterized by a six line signal, indicating a secondary carbon-centered radical and attributed to a resonant ALA√ radical. Iron is also released in such anaerobic electrochemical oxidations of ALA in the presence of ferritin, suggesting that, in addition to O₂^•−, ALA√ can promote iron mobilization from ferritin. Hence, ALA√ may amplify the metal-catalyzed oxidation of ALA, damaging ALA-accumulating cells and possibly contributing to the symptoms of porphyria.     

Possible role of the polyuronic components in accumulation and mobilization of iron and phosphate at the soil--root interface.

With the aim to investigate the role of the polyuronic components in the accumulation of iron and phosphate at the soil-root interface, the interactions of Ca-polygalacturonates (PGAs) with Fe(III) and P ions and of Fe(III)-Ca-polygalacturonates (Fe-PGAs) with P ions were studied at pH 4.7. The role of citric, malic and pyruvic acids in the mobilization of Fe(III) and P, in the presence and absence of Ca(II) 2.5mM, was also investigated. The sorption kinetics evidenced that P diffuses freely through the calcium polysaccharidic matrix whereas Fe(III) accumulates as an hydroxypolymer. The sorption kinetics of P by the Fe-PGA indicated that the amount of P sorbed increases with increasing its initial concentration up to a constant value equal to 0.98micromol/3.87micromolmg(-1) of Fe(III)-polymer trapped. The FT-IR spectra of the P-Fe-PGA systems, show bands attributable to P-O(H) stretching vibrations. The study of systems with a constant initial P amount and varying Fe(III) amounts allowed to hypothesize that phosphate settles down inside holes formed by the carboxylate groups of galacturonic units. Citric and malic acids showed to be active in the mobilization of both Fe and P whereas pyruvic acid appeared inactive.     

Effect of phosphate on bacterioferritin-catalysed iron(II) oxidation

The iron(III) mineral cores of bacterioferritins (BFRs), as isolated, contain a significant component of phosphate, with an iron-to-phosphate ratio approaching 1:1 in some cases. In order to better understand the in vivo core-formation process, the effect of phosphate on in vitro core formation in Escherichia coli BFR was investigated. Iron cores reconstituted in the presence of phosphate were found to have iron-to-phosphate ratios similar to those of native cores, and possessed electron paramagnetic resonance properties characteristic of the phosphate-rich core. Phosphate did not affect the stoichiometry of the initial iron(II) oxidation reaction that takes place at the intrasubunit dinuclear iron-binding sites (phase 2 of core formation), but did increase the rate of oxidation. Phosphate had a more significant effect on subsequent core formation (the phase 3 reaction), increasing the rate up to five-fold at pH 6.5 and 25 °C. The dependence of the phase 3 rate on phosphate was complex, being greatest at low phosphate and gradually decreasing until the point of saturation at ~2 mM phosphate (for iron(II) concentrations <200 M). Phosphate caused a significant decrease in the absorption properties of both phase 2 and phase 3 products, and the phosphate dependence of the latter mirrored the observed rate dependence, suggesting that distinct iron(III)-phosphate species are formed at different phosphate concentrations. The effect of phosphate on absorption properties enabled the observation of previously undetected events in the phase 2 to phase 3 transition period.Abbreviations BFR Bacterioferritin - EcBFR Escherichia coli BFR - PaBFR Pseudomonas aeruginosa BFR - AvBFR Azotobacter vinelandii BFR - ITPG Isopropyl -d-thiogalactopyranoside - MES 2-(N-morpholino)-ethanesulfonic acid     

Response of a zooplankton community to the addition of unsaturated fatty acids: an enclosure study

1. The effect of the addition of emulsions with different fatty acid composition to a semi-natural zooplankton community was studied in enclosures.
2. The reactions of different taxa in the zooplankton community to the addition of the emulsions were different. The copepods showed almost no reaction, nor did the selective cladocerans ( Bosmina ) or rotifers ( Synchaeta or Polyarthra ). The non-selective filterfeeding cladocerans Daphnia and Ceriodaphnia , and the rotifer Keratella , showed responses to the addition of the emulsions.
3.  Keratella showed the highest density in the enclosures with high amounts of highly unsaturated fatty acids added, whereas both Daphnia and Ceriodaphnia reached the highest numbers in the enclosures where we added emulsions of saturated fatty acids only.
4. Our results suggest that different taxa may be limited by different factors, even though they use similar food sources. Hence, we conclude that it is very difficult to generalize on the limiting factors in aquatic systems.     

Manganese(II), iron(II) and nickel(II) chloride complexes with monodeprotonated anionic guanine

Upon refluxing 2:1 mixtures of guanine (guH) and MnCl₂, FeCl₂ or NiCl₂ in a 7:3 (v/v) mixture of ethanol and triethyl orthoformate for 1–2 weeks, partial substitution of gu^? for Cl^? groups occurs, and solid complexes of the M(gu)Cl·2ROH (R = C₂H₅ for M = Mn; R = H for M = Fe, Ni) type are obtained. The new complexes are pentacoordinated and appear to be linear chainlike polymeric species, involving a single-bridged

_n backbone. Coordination number five is attained by the presence of one terminal chloro and two terminal ROH ligands per metal ion. Most probable binding sites of bidentate bridging gu^? are the N(7) and N(9) imidazole ring nitrogens. IR evidence rules out the possibility of coordination of gu^? through any of the exocyclic potential ligand sites (O(6) oxygen or N(2) nitrogen) [1].     

The influence of light and nutrient addition upon the sediment chemistry of iron in an arctic lake

The geochemical response of sediments to increased nutrient input to an Alaskan, arctic lake was examined using direct measurements of sediment-water chemical fluxes. An unexpected increase in Fe flux occurred when sediments were exposed to high incident radiation and nutrient concentrations. Correlation between light and acid-soluble Fe concentrations suggests that photoreduction of Fe(III) oxides may occur, but nutrient addition enhanced the effect indicating that primary productivity was also important. The processes controlling the flux of Fe from sediments in this lake were complex and included the redox potential (dissolved oxygen concentration) of the water, quality of organic matter present in the sediment, light, and nutrients supplied from the sediments and/or water column. These four factors together with the possibility of direct uptake of Fe by phytoplankton and the possible release of algal reductants may contribute to Fe cycling in this lake.     

Effects of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community of a deep,tropical reservoir: an enclosure experiment

1. An in situ enclosure experiment was conducted in a deep reservoir of southern China to examine (i) the effects of a low biomass (4 g wet weight m^?3) of silver carp (Hypophthalmichthys molitrix) and nutrients on the plankton community and (ii) the response of Daphnia to eutrophication. 2. In the absence of fish, Daphnia galeata dominated the zooplankton community, whereas calanoids were dominant in the fish treatments, followed by D. galeata. Silver carp stocking significantly reduced total zooplankton biomass, and that of D. galeata and Leptodorarichardi, but markedly increased the biomass of smaller cladocerans, copepod nauplii and rotifers. In contrast, nutrient enrichment had no significant effect on the plankton community except for cyclopoids. 3. Chlorophyta, Cryptophyta and Bacillariophyta were dominant phytoplankton groups during the experiment. Chlorophyta with high growth rates (mainly Chlorella vulgaris in the fish enclosures and Ankyra sp. in the fishless enclosures) eventually dominated the phytoplankton community. Total phytoplankton biomass and the biomass of edible phytoplankton [greatest axial linear dimension (GALD) < 30 μm], Chlorophyta, Cryptophyta, Bacillariophyta and Cyanobacteria showed positive responses to fish stocking, while inedible phytoplankton (GALD ≥ 30 μm) was significantly reduced in the fish enclosures. However, there was no significant effect on the plankton community from the interaction of fish and nutrients. 4. Overall, the impact of fish on the plankton community was much greater than that of nutrients. High total phosphorus concentrations in the control treatment and relatively low temperatures may reduce the importance of nutrient enrichment. These results suggest it is not appropriate to use a low biomass of silver carp to control phytoplankton biomass in warmer, eutrophic fresh waters containing large herbivorous cladocerans.     

Predation by underyearling perch (Perca fluviatilis) on a Daphnia galeata population in a short-term enclosure experiment

1. The predation impact of underyearling perch (20 mm total length) on the dynamics of Daphnia galeata was studied in three 6.5-m³ enclosures during a 17-day experiment in June 1995. These data were compared with zooplankton succession in three fish-free control enclosures and in the pelagic zone of Bautzen reservoir, Germany. 2. Due to individual growth during the experiment, fish biomass in the enclosures increased from 210 mg wet body mass (w.b.m.) m^–3 to 830 mg w.b.m. m^–3, equivalent to an increase from 20 kg ha^–1 to 75 kg ha^–1. 3. In the enclosures with fish, biomass of daphnids decreased steadily to values below 1 mg wet weight (w.w.) l^–1 within 17 days, whereas in the fish-free controls and in Bautzen reservoir the Daphnia biomass fluctuated around 8 mg w.w. l^–1. Other zooplankton species exhibited little or no change. Approximately 60 kg ha^–1 was calculated as the critical underyearling perch biomass which may induce a drastic decline of the Daphnia galeata population in Bautzen reservoir. Comparison with values from other lakes is difficult due to differences in water depths and Daphnia biomasses. 4. Mean individual biomass of daphnids, egg ratio and proportion of adult daphnids were significantly lower in the enclosures with fish compared with the control enclosures at the end of the experiment. This may be explained partly by preferential predation of the large, egg-carrying daphnids by fish. However, no difference was found in clutch size and size at first reproduction, possibly due to the short duration of the experiment. 5. It must be assumed that the ‘summer depression’ of daphnids observed in many waters is not the exclusive effect of direct reduction of daphnids by fish predation. Even the high biomass of underyearling perch stocked in the enclosures did not completely account for Daphnia mortality. Instead, the selective loss of large size classes, combined with low food resources and reduced reproduction rates, may induce the marked declines in daphnids.     

Selective addressing of heteroditopic ligands by iron(II) and platinum(II)

The heteroditopic ligand 4′-(4,7,10-trioxadec-1-yn-10-yl)-2,2′:6′,2″-terpyridine, 2, contains an N,N′,N″-donor metal-binding domain that recognizes iron(II), and a terminal alkyne site that selectively couples to platinum(II). This selectivity has been used to investigate routes to the formation of heterometallic systems. The single crystal structures of ligand 2 and the complex [Fe(2)₂][PF₆]₂ are reported.     

Mutation in nicotianamine aminotransferase stimulated the Fe(II) acquisition system and led to iron accumulation in rice

Higher plants acquire iron (Fe) from the rhizosphere through two strategies. Strategy II, employed by graminaceous plants, involves secretion of phytosiderophores (e.g. deoxymugineic acid in rice [Oryza sativa]) by roots to solubilize Fe(III) in soil. In addition to taking up Fe in the form of Fe(III)-phytosiderophore, rice also possesses the strategy I-like system that may absorb Fe(II) directly. Through mutant screening, we isolated a rice mutant that could not grow with Fe(III)-citrate as the sole Fe source, but was able to grow when Fe(II)-EDTA was supplied. Surprisingly, the mutant accumulated more Fe and other divalent metals in roots and shoots than the wild type when both were supplied with EDTA-Fe(II) or grown under water-logged field conditions. Furthermore, the mutant had a significantly higher concentration of Fe in both unpolished and polished grains than the wild type. Using the map-based cloning method, we identified a point mutation in a gene encoding nicotianamine aminotransferase (NAAT1), which was responsible for the mutant phenotype. Because of the loss of function of NAAT1, the mutant failed to produce deoxymugineic acid and could not absorb Fe(III) efficiently. In contrast, nicotianamine, the substrate for NAAT1, accumulated markedly in roots and shoots of the mutant. Microarray analysis showed that the expression of a number of the genes involved in Fe(II) acquisition was greatly stimulated in the naat1 mutant. Our results demonstrate that disruption of deoxymugineic acid biosynthesis can stimulate Fe(II) acquisition and increase iron accumulation in rice.     

RNA folding and catalysis mediated by iron (II)

Mg2? shares a distinctive relationship with RNA, playing important and specific roles in the folding and function of essentially all large RNAs. Here we use theory and experiment to evaluate Fe2? in the absence of free oxygen as a replacement for Mg2? in RNA folding and catalysis. We describe both quantum mechanical calculations and experiments that suggest that the roles of Mg2? in RNA folding and function can indeed be served by Fe2?. The results of quantum mechanical calculations show that the geometry of coordination of Fe2? by RNA phosphates is similar to that of Mg2?. Chemical footprinting experiments suggest that the conformation of the Tetrahymena thermophila Group I intron P4-P6 domain RNA is conserved between complexes with Fe2? or Mg2?. The catalytic activities of both the L1 ribozyme ligase, obtained previously by in vitro selection in the presence of Mg2?, and the hammerhead ribozyme are enhanced in the presence of Fe2? compared to Mg2?. All chemical footprinting and ribozyme assays in the presence of Fe2? were performed under anaerobic conditions. The primary motivation of this work is to understand RNA in plausible early earth conditions. Life originated during the early Archean Eon, characterized by a non-oxidative atmosphere and abundant soluble Fe2?. The combined biochemical and paleogeological data are consistent with a role for Fe2? in an RNA World. RNA and Fe2? could, in principle, support an array of RNA structures and catalytic functions more diverse than RNA with Mg2? alone.     

Kinetics and mechanism of iron(III) complexation by ferric binding protein: the role of phosphate

Iron transport across the periplasmic space to the cytoplasmic membrane of certain Gram-negative bacteria is mediated by a ferric binding protein (Fbp). This requires Fe(3+) loading of Fbp at the inner leaflet of the outer membrane. A synergistic anion is required for tight Fe(3+) sequestration by Fbp. Although phosphate fills this role in the protein isolated from bacterial cell lysates, nitrilotriacetate anion (NTA) can also satisfy this requirement in vitro. Here, we report the kinetics and mechanism of Fe(3+) loading of Fbp from Fe(NTA)(aq) in the presence of phosphate at pH 6.5. The reaction proceeds in four kinetically distinguishable steps to produce Fe(3+)Fbp(PO(4)) as a final product. The first three steps exhibit half-lives ranging from ca. 20 ms to 0.5 min, depending on the concentrations, and produce Fe(3+)Fbp(NTA) as an intermediate product of significant stability. The rate for the first step is accelerated with an increasing phosphate concentration, while that of the third step is retarded by phosphate. Conversion of Fe(3+)Fbp(NTA) to Fe(3+)Fbp(PO(4)) in the fourth step is a slow process (half-life approximately 2 h) and is facilitated by free phosphate. A mechanism for the Fe(3+)-loading process is proposed in which the synergistic anions, phosphate and NTA, play key roles. These data suggest that not only is a synergistic anion required for tight Fe(3+) sequestration by Fbp, but also the synergistic anion plays a critical role in the process of inserting Fe(3+) into the Fbp binding site.     

Complexation of iron(III) and iron(II) by citrate. Implications for iron speciation in blood plasma

Estimates of the concentrations and identity of the predominant complexes of iron with the low-molecular-mass ligands in vivo are important to improve current understanding of the metabolism of this trace element. These estimates require a knowledge of the stability of the iron-citrate complexes. Previous studies on the equilibrium properties of the Fe(III)-citrate and Fe(II)-citrate are in disagreement. Accordingly, in this work, glass electrode potentiometric titrations have been used to re-determine the formation constants of both the Fe(III)- and Fe(II)-citrate systems at 25 degrees C in 1.00 M (Na)Cl and the reliability of these constants has been evaluated by comparing the measured and predicted redox potentials of the ternary Fe(III)-Fe(II)-citrate system. The formation constants obtained in this way were used in computer simulation models of the low-molecular-mass iron fraction in blood plasma. Redox equilibria of iron are thus included in large models of blood plasma for the first time. The results of these calculations show the predominance of Fe(II)-carbonate complexes and a significant amount of aquated Fe(II) in human blood plasma.     

Intramolecular oxidation of the ligand 4-methyl-2-N-(2-pyridylmethyl)aminophenol (Hpyramol) upon coordination with iron(II) chloride and manganese(II) perchlorate

The ligand Hpyramol (Hpyramol=4-methyl-2-N-(2-pyridylmethyl)aminophenol) is found to undergo an oxidative dehydrogenation of its amine function to an imine group upon coordination with iron(II) chloride and manganese(II) perchlorate. X-ray diffraction analyses for both complexes shows differences in the coordination geometry of the complexes most likely because of the two different counter-ions namely the strong coordinating chloride anions and the weak coordinating perchlorate anions. The coordination sphere of the iron(III) complex in [FeCl₂(pyrimol)(MeOH)](MeOH) is best described as a distorted octahedral FeN₂O₂Cl₂ chromophore, while the manganese(II) ions in [Mn(ClO₄)(pyrimol)(Hpyrimol)]₂ are in a distorted octahedral MnN₄O₂ environment with a 2:1 ligand to metal ratio instead of 1:1.     

The requirement for iron (III) in the initiation of lipid peroxidation by iron (II) and hydrogen peroxide

The initiation of lipid peroxidation by Fe2+ and H2O2 (Fenton's reagent) is often proposed to be mediated by the highly reactive hydroxyl radical. Using Fe2+, H2O2, and phospholipid liposomes as a model system, we have found that lipid peroxidation, as assessed by malondialdehyde formation, is not initiated by the hydroxyl radical, but rather requires Fe3+ and Fe2+. EPR spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide and the bleaching of para-nitrosodimethylaniline confirmed the generation of the hydroxyl radical in this system. Accordingly, catalase and the hydroxyl radical scavengers mannitol and benzoate efficiently inhibited the generation and the detection of hydroxyl radical. However, catalase, mannitol, and benzoate could either stimulate or inhibit lipid peroxidation. These unusual effects were found to be consistent with their ability to modulate the extent of Fe2+ oxidation by H2O2 and demonstrated that lipid peroxidation depends on the Fe3+:Fe2+ ratio, maximal initial rates occurring at 1:1. These studies suggest that the initiation of liposomal peroxidation by Fe2+ and H2O2 is mediated by an oxidant which requires both Fe3+ and Fe2+ and that the rate of the reaction is determined by the absolute Fe3+:Fe2+ ratio.