Belli, SI, Walker, RA & Flowers, SA 2005, 'Global protein expression analysis in apicomplexan parasites: Current status', Proteomics, vol. 5, no. 4, pp. 918-924.
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Members of the phylum Apicomplexa are important protozoan parasites that cause some of the most serious, and in some cases, deadly diseases in humans and animals. They include species from the genus Plasmodium, Toxoplasma, Eimeria, Neospora, Cryptosporid
Bengtson Nash, S, Schreiber, U, Ralph, PJ & Muller, JF 2005, 'The combined SPE: Tox Y-PAM phytotoxicity assay; application and appraisal of a novel Biomonitoring tool for the aquatic environment', Biosensors and Bioelectronics, vol. 20, no. 7, pp. 1443-1451.
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Mounting concerns regarding the environment impact of herbicides has meant a growing requirement for accurate, timely information regarding herbicide residue contamination of, in particular, aquatic systems. Conventional methods of detection remain limited in temrns of practicality due to high costs of oeration and the specialised information that analysis provides. A new phytotoxicity bioassay wa trialled for the detection of herbicide residues in filter-purified (Milli-Q) as sell as antural waters. The performance of the system, which combines solid-phase extraction (SPE) wtih the ToxY-PAM dual-channel yield annalyser (Heinz Walz GmbH), was tested alongside the traditional method of liquid chromatography-mass spectometry (LC-MS). The assay methodology was found to be highly sensitive (LOD 0.1 ngL-1 diuron) with good reproducibility. The study showed that the assay protocol is time effective and can be employed for the aquatic screening of herbicide residues in purified as well as natural waters.
Charpy-Roubaud, C & Larkum, AWD 2005, 'Dinitrogen fixation by exposed communities on the rim of Tikehau atoll (Tuamotu Archipelago, French Polynesia)', Coral Reefs, vol. 24, no. 4, pp. 622-628.
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Various types of sub-aerially exposed microbial mats, including emergent mats, beach sand, beach rock and Kopara mats, are widespread on the 78 km (25 km2) of rim surrounding the Tikehau atoll lagoon. These mats form laminated accretions or diffuse microbial communities growing under high insolation and temperatures, and are therefore subject to desiccation. Both heterocystous and non-heterocystous cyanobacteria occur in these mats. Using acetylene reduction techniques, nitrogenase activity was observed at all sites over a period of 5 years and was 3-17 times higher during daylight than at night in all communities except for beach rock. 15N2 measurements indicated a molar ratio of acetylene reduction to N2 fixed of 1.6 for all exposed communities. Estimated N2 fixation ranged from 1.44 to 8.0 mg N m-2 day-1 in these exposed communities (mean of 4.66 mg N m-2 day-1) with beachrock showing the highest rates. For the whole reef rim, daily N2 fixation amounted to 98.42 kg N day-1 which represents 28% of the rate of fixation in the entire lagoon (area 400 km2). © Springer-Verlag 2005.
Chen, M, Bibby, TS, Nield, J, Larkum, A & Barber, J 2005, 'Iron deficiency induces a chlorophyll d-binding Pcb antenna system around Photosystem I in Acaryochloris marina', Biochimica et Biophysica Acta - Bioenergetics, vol. 1708, no. 3, pp. 367-374.
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The prochlorophyte-like cyanobacterium Acaryochloris marina contains two pcb genes, pcbA and pcbC, which encode chlorophyll (Chl) d-binding antenna proteins PcbA and PcbC, respectively. Using real-time reverse transcriptase polymerase chain reaction (RT-PCR), it is shown that when Acaryochloris cells are grown in an iron-deficient medium, the transcription of the pcbC gene is up-regulated compared to that of pcbA. Biochemical and immunological analyses indicated that under the same iron-deficient conditions, the level of Photosystem I (PSI) decreased compared with that of Photosystem II (PSII). Electron microscopy revealed that concomitant with these changes was the formation of Pcb-PSI supercomplexes which, in their largest form, were composed of 18 Pcb subunits forming a ring around the trimeric PSI reaction centre core. Mass spectrometry indicated that the PcbC protein is the main constituent of this outer PSI antenna system. It is therefore concluded that in Acaryochloris, the PcbC protein forms an antenna for PSI when iron levels become limiting and in this way compensates for the drop in the level of PSI relative to PSII which occurs under these conditions. © 2005 Elsevier B.V. All rights reserved.
Chen, M, Bibby, TS, Nield, J, Larkum, AWD & Barber, J 2005, 'Structure of a large photosystem II supercomplex from Acaryochloris marina', FEBS Letters, vol. 579, no. 5, pp. 1306-1310.
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Acaryochloris marina is a prochlorophyte-like cyanobacterium containing both phycobilins and chlorophyll d as light harvesting pigments. We show that the chlorophyll d light harvesting system, composed of Pcb proteins, functionally associates with the photosystem II (PSII) reaction center (RC) core to form a giant supercomplex. This supercomplex has a molecular mass of about 2300 kDa and dimensions of 385 Å x 240 Å. It is composed of two PSII-RC core dimers arranged end-to-end, flanked by eight symmetrically related Pcb proteins on each side. Thus each PSII-RC monomer has four Pcb subunits acting as a light harvesting system which increases the absorption cross section of the PSII-RC core by almost 200%. © 2005 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.
Chen, M, Eggink, LL, Hoober, JK & Larkum, AWD 2005, 'Influence of structure on bindinq of chlorophylls to peptide ligands', Journal of the American Chemical Society, vol. 127, no. 7, pp. 2052-2053.
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Four classes of chlorophyll (Chl), a, b, c, and d, are involved in photosynthesis within cyanobacteria, algae, and plants. These classes have different evolutionary origins, chemical properties, and biological functions. Our results demonstrate that peptide-bound ligands provided by the imidazole group of histidine and the charge-compensated glutamate-arginine ion pair readily form coordination bonds with Chls a and d but do not interact significantly with Chls b and c. These ligands are apparently not sufficiently strong Lewis bases to displace strongly coordinated water from Chls b and c. These differences determine specificity of binding of Chls in light-harvesting complexes and play an important role in assembly of stable Chl-protein complexes, which has had a profound impact on the evolution of photosynthetic organisms. Copyright © 2005 American Chemical Society.
Chen, M, Hiller, RG, Howe, CJ & Larkum, AWD 2005, 'Unique origin and lateral transfer of prokaryotic chlorophyll-b and chlorophyll-d light-harvesting systems', Molecular Biology and Evolution, vol. 22, no. 1, pp. 21-28.
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pcb genes, encoding proteins binding light-harvesting chlorophylls, were cloned and sequenced from the Chl d-containing cyanobacterium, Acaryochloris marina, and the Chl b-containing cyanobacterium, Prochloron didemni. Both organisms contained two tandem pcb genes. Peptide fingerprinting confirmed the expression of one of the A. marina pcb genes. Phylogenetic tree reconstruction using distance-matrix and maximum-likelihood methods indicated a single origin of the pcb gene family, whether occurring in Chl b-containing or Chl d-containing organisms. This may indicate widespread lateral transfer of the Pcb protein-based light-harvesting system.
Chen, M, Telfer, A, Lin, S, Pascal, A, Larkum, AWD, Barber, J & Blankenship, RE 2005, 'The nature of the photosystem II reaction centre in the chlorophyll d-containing prokaryote, Acaryochloris marina', Photochemical and Photobiological Sciences, vol. 4, no. 12, pp. 1060-1064.
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Pigment-protein complexes enriched in photosystem II (PS II) have been isolated from the chlorophyll (Chl) d containing cyanobacterium, Acaryochloris marina. A small PS II-enriched particle, we call 'crude reaction centre', contained 20 Chl d, 0.5 Chl a and 1 redox active cytochrome b-559 per 2 pheophytin a, plus the D1 and D2 proteins. A larger PS II-enriched particle, we call 'core', additionally bound the antenna complexes, CP47 and CP43, and had a higher chlorophyll per pheophytin ratio. Pheophytin a could be photoreduced in the presence of a strong reductant, indicating that it is the primary electron acceptor in photosystem II of A. marina. A substoichiometric amount of Chl a (less than one chlorophyll a per 2 pheophytin a) strongly suggests that Chl a does not have an essential role in the photochemistry of PS II in this organism. We conclude that PS II, in A. marina, utilizes Chl d and not Chl a as primary electron donor and that the primary electron acceptor is one of two molecules of pheophytin a. © The Royal Society of Chemistry and Owner Societies 2005.
Coyne, K, Handy, S, Demir, E, Whereat, E, Hutchins, DA, Portune, K, Doblin, MA & Cary, S 2005, 'Improved quantitative real-time PCR assays for enumeration of harmful algal species in field samples using an exogenous DNA reference standard', Limnology and Oceanography: Methods, vol. 3, pp. 381-391.
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Quantitative real-time PCR (QPCR) is a powerful and sensitive method for quantitative detection of microorganisms. Application of this methodology for enumeration of harmful algal bloom (HAB) species has the potential to revolutionize our approach to HAB research, making it possible to identify correlations between cell abundances and factors that regulate bloom dynamics. Its application to ecological studies, however, has produced mixed results. QPCR assays typically rely of the generation of standard curves from plasmids or laboratory cultures that may be unrealistic whencompared to amplification of DNA extracted from field samples. In addition, existing methods often fail to incorporate controls to assess variability in extraction and amplification efficiencies,or include controls that are sequence-specific and preclude the investigation of multiple species. Here, we describe the development and rigorous analysis of QPCR awways for two HAB species, Chattonella subsala and Heterosigma akashiwo, in which we introduce a known concentration of exogenous DNA plasmid into the extraction buffer as a refernce standard. Since the target DNA is extracted in the presence of the reference standard, inherent variability in extraction and amplification efficiencies affect both target and standard equally. Furthermore, the reference standard is application to QPCR analysis of any microbial species. Using environmental bloom samples as calibrators, we evaluated the accuracy of the comparative Ct method for enumeration of target species in several field smaples, Out investigation demonstrates that the comparative Ct method with an exogenous DNA reference standard provides both accurate and reproducible quantification of HAB species in environmental samples.
Drake, L, Meyer, A, Forsberg, R, Baier, R, Doblin, MA, Heinemann, SH, Johnson, W, Koch, M, Roblee, P & Dobbs, FC 2005, 'Potential invasion of microorganisms and pathogens via 'interior hull fouling': biofilms inside ballast water tanks', Biological Invasions, vol. 7, pp. 969-982.
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Surfaces submerged in an aquatic milieu are covered to some degree with biofilms - organic matrices that can contain bacteria, microalgae, and protozoans, sometimes including disease-causing forms. One unquantified risk of aquatic biological invatsions is the potential for biofilms within ships' ballast water tanks to harbour pathogens, and, in tuen, seed othe waters. To begin to evaluate this vector, we collected biofilm samples fromtanks' surfaces and deployed controlled-surface sampling units within tanks. We then measured a variety of microbial metrics within the biofilms to test the hypotheses that pathogens are present in biofilms and that biofilms have higher microbial densities compared to ballst water. Field experiments and sampling of coastwise and oceangoing ships arriving at ports in Chesapeake Bay and the North American Great Lakes showed the presence of abundant microorganisms, including pathogens, in biofilms. These results suggest that ballast-tank biofilms represent an additional risk of microbial invasion, provided they release cells into the water or they are sloughed off during normal ballasting operations.
Ferris, MJ, Sheehan, KB, Kuhl, M, Cooksey, K, Wigglesworth-Cooksey, B, Harvey, R & Henson, JM 2005, 'Algal Species and Light Microenvironment in a Low-pH, Geothermal Microbial Mat Community', Applied and Environmental Microbiology, vol. 71, no. 11, pp. 7164-7171.
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nicellular algae are the predominant microbial mat-forming phototrophs in the extreme environments of acidic geothermal springs. The ecology of these algae is not well known because concepts of species composition are inferred from cultivated isolates and microscopic observations, methods known to provide incomplete and inaccurate assessments of species in situ. We used sequence analysis of 18S rRNA genes PCR amplified from mat samples from different seasons and different temperatures along a thermal gradient to identify algae in an often-studied acidic (pH 2.7) geothermal creek in Yellowstone National Park. Fiber-optic microprobes were used to show that light for algal photosynthesis is attenuated to <1% over the 1-mm surface interval of the mat. Three algal sequences were detected, and each was present year-round.
Handy, S, Coyne, K, Portune, K, Demir, E, Doblin, MA, Hare, CE, Cary, S & Hutchins, DA 2005, 'Evaluating vertical migration behaviour of harmful raphidophytes in the Delaware Inland Bays utilizing quantitative real-time PCR', Aquatic Microbial Ecology, vol. 40, pp. 121-132.
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Mixed blooms of 4 species of harmful raphidophytes (Chattonella cf. verruculosa, Chattonella subsalsa, Heterosigma akashiwo, and Fibrocapsa japonica) occur in the shallow (1 ti 2m) Delaware Inland Bays (DIB), USA. Raphidophytes vertically migrate in other deeper water ecosystems to utilise deep nutrient stocks at night, and thus obtain an advantage over non-migrating algae.Anoxic DIB sediments release high levels of bioavailable phosphate, which could potentially be used by vertically migrating flagellates. This study aimed to characterise and understamd the migration oatterns of DIB raphidiphytes, and determine whether benthic phosphate fluxes could provide the cells with P. We demonstrated vertical migration of isolated DIB raphidophyte cultures in the laboratory, where differences inthe response of C. subsalsa and H. akashiwo to light:dark period manipulations suggested possible diffeerneces in external versus endogenous regulation of migration behaviour in the 2 species. Natural blooms in the filed (enclosed in a mesocosm system) also exhibited patterns of diel vertical distributions of each species. Our data suggested that these 2 photoautotrophic species spend daylight hours near the surface and are found directly on the sediment surface at night. However, diel changes in particulate C:P ratios did not support the hypothesis that there is preferential uptake of sedimentary phosphate at night. Our results also suggested that the migration behaviour may have important implications for designing sampling strategies for monitoring programs. QPCR has a number of decisive advantages over traditional microscopic counting methods, making this a poweful tool for fine spatial temporal scale detection and enum,eration of vertically migrating harmful algal species.
Hawe, I, Schwarz, A-M, Sutherland, DL & Howard-Williams, C 2005, 'Aquatic Ecosystems of the McMurdo Dry Valleys – the edge of survival', Water and Atmosphere, vol. 11, no. 3, pp. 16-17.
Hill, R & Ralph, PJ 2005, 'Diel and seasonal changes in fluorescence rise kinetics of three scleractinian corals', Functional Plant Biology, vol. 32, no. 6, pp. 549-559.
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The effect of diel oscillations in light on the photosynthetic response of three coral species during summer and winter was studied. Fast induction curves revealed detailed information on primary photochemistry as well as redox states of electron accepto
Hill, R, Frankart, C & Ralph, PJ 2005, 'Impact of bleaching conditions on the components of non-photochemical quenching in the zooxanthellae of a coral', Journal Of Experimental Marine Biology And Ecology, vol. 322, no. 1, pp. 83-92.
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Mass coral bleaching events are a worldwide phenomenon, which generally occur during periods of elevated sea surface temperature and intense sunlight. These conditions result in a decline in photochemical efficiency of symbiotic microalgae (zooxanthellae
Jensen, SI, Kuhl, M, Glud, RN, Jorgensen, LB & Prieme, A 2005, 'Oxic microzones and radial oxygen loss from roots of Zostera marina', Marine Ecology Progress Series, vol. 293, pp. 49-58.
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Oxygen microelectrodes and planar oxygen optodes were used to map the microdistribution of oxygen and the radial oxygen loss (ROL) from roots of Zostera marina kept in natural sediment. Substantial heterogeneity in the oxygen distribution was seen along the roots, with oxygen mainly leaking out from the root tips. Maximum oxygen levels at the root surface reached 19 to 80% of air saturation in the light and the oxygenated zone extended 1 to 2 mm away from the root tip. The oxygen concentration at the root surface decreased to 05% of air saturation at positions 3 to 6 mm behind the root apex. The high oxygen levels at the root tip surface were due to an effective barrier to ROL on the older part of the roots and the presence of an effective gas-transport system in the plant, with numerous intercellular spaces extending very close to the apical meristem of the root. Radial diffusion of oxygen from the root surface created a dynamic 0 to 1 mm-wide oxic microzone around the ~0.3 mm wide roots of Z. marina that varied with irradiance and distance from the root tip. Root-surface oxygen concentrations and ROL measured 2 mm behind the apex increased with increasing irradiance until ROL saturation was reached at irradiances >400 µmol photons m2 s1. The ROL increased from 16.2 nmol O2 cm2 h1 in darkness to 21.6, 28.8 and 36.0 nmol O2 cm2 h1 at incident irradiances of 25, 111 and 467 µmol photons m2 s1, respectively. Based on measured steady-state radial oxygen profiles, the total oxygen export from one 6 cm long root of the first actively growing root bundle with a total surface area of 0.56 cm2 was estimated to be 6.0 to 6.7 nmol O2 h1 in saturating light.
Konig, B, Kohls, O, Holst, G, Glud, RN & Kuhl, M 2005, 'Fabrication and test of sol-gel based planar oxygen optodes for use in aquatic sediments', Marine Chemistry, vol. 97, no. 3-4, pp. 262-276.
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We describe the fabrication of organically modified solgel (ORMOSIL) planar optodes for mapping the two-dimensional oxygen distribution in sediments. All sensor foils were based on the use of ruthenium(II)-tris-(4,7-diphenyl-1,10-phenantrolin)- perchlorate, which is a fluorescent dye quenched dynamically by oxygen. Sensors made with different solgel immobilisation matrices, different concentrations of precursors and indicator dye, as well as different types of scattering particles coimmobilised in the sensor foil were investigated systematically. Optimal sensor performance was obtained with dye concentrations of 210 mmol/kg in an immobilisation matrix made of diphenyldiethoxy-silan and phenyltriethoxy-silan precursors with addition of organically coated TiO2 particles. The sensors exhibited a good mechanical stability and a high sensitivity from 0% to 100% oxygen, which remained constant over at least 36 days. The planar optodes were used with a fluorescent lifetime imaging system for direct mapping of the spatio-temporal variation in oxygen distribution within marine sediment inhabited by the polychaete Hediste diversicolor. The measurements demonstrated the spatio-temporal heterogeneity of the oxygen distribution in bioturbated sediments due to burrow structures and non-constant irrigation activity of the polychaete, which is difficult to resolve with microsensors or with traditional biogeochemical techniques.
Kuehl, M, Chen, M, Ralph, PJ, Schreiber, U & Larkum, A 2005, 'A niche for cyanobacteria containing chlorophyll d', Nature, vol. 433, no. 1, pp. 820-820.
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The cyanobacterium known as Acaryochloris marina is a unique phototroph that uses chlorophyll d as its principal light-harvesting pigment instead of chlorophyll a, the form commonly found in plants, algae and other cyanobacteria; this means that it depends on far-red light for photosynthesis. Here we demonstrate photosynthetic activity in Acaryochloris-like phototrophs that live underneath minute coral-reef invertebrates (didemnid ascidians) in a shaded niche enriched in near-infrared light. This discovery clarifies how these cyanobacteria are able to thrive as free-living organisms in their natural habitat.
Kuhl, M 2005, 'Optical microsensors for analysis of microbial communities', Methods in Enzymology, vol. 397, pp. 166-199.
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Fiber]optic microprobes connected to sensitive light meters are ideal tools to resolve the steep gradients of light intensity and spectral composition that prevail in aggregates and surface]associated microbial communities in sediments, biofilms, and microbial mats. They allow for a detailed mapping of light fields and enable insights to the complex optical properties of such highly light]scattering and ]absorbing microbial systems. Used in combination with microsensors for chemical species, fiber]optic irradiance microprobes allow for detailed studies of photosynthesis regulation and of the photobiology of microbial phototrophs in intact samples under ambient microenvironmental conditions of the natural habitat. Fiber]optic microprobes connected to sensitive fluorometers enable microscale fluorescence measurements, which can be used to map (i) diffusivity and flow; (ii) distribution of photosynthetic microbes, via their photopigment autofluorescence; and (iii) activity of oxygenic photosynthesis via variable chlorophyll fluorescence measurements.
Larkum, A & Kuhl, M 2005, 'Chlorophyll d: the puzzle resolved', Trends in Plant Science, vol. 10, no. 8, pp. 355-357.
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Chlorophyll a (Chl a) has always been regarded as the sole chlorophyll with a role in photochemical conversion in oxygen-evolving phototrophs, whereas chlorophyll d (Chl d), discovered in small quantities in red algae in 1943, was often regarded as an artefact of isolation. Now, as a result of discoveries over the past year, it has become clear that Chl d is the major chlorophyll of a freeliving and widely distributed cyanobacterium that lives in light environments depleted in visible light and enhanced in infrared radiation. Moreover, Chl d not only has a light-harvesting role but might also replace Chl a in the special pair of chlorophylls in both reactions centers of photosynthesis.
Macinnis-Ng, CM, Morrison, DJ & Ralph, PJ 2005, 'Temporal and spatial variation in the morphology of the brown macroalga Hormosira banksii (Fucales, Phaeophyta)', Botanica Marina, vol. 48, no. 3, pp. 198-207.
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Hormosira banksii is a morphologically variable macroalgal species from southeastern and southern Australia, which has been previously categorised into ecoforms according to habitat. This study is by far the largest quantitative evaluation of morphologic
Moore, LR, Ostrowski, M, Scanlan, DJ, Feren, K & Sweetsir, T 2005, 'Ecotypic variation in phosphorus acquisition mechanisms within marine picocyanobacteria', AQUATIC MICROBIAL ECOLOGY, vol. 39, no. 3, pp. 257-269.
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Murray, SA, Jorgensen, MF, Ho, SY, Patterson, DJ & Jermiin, LS 2005, 'Improving the analysis of dinoflagellate phylogeny based on rDNA', Protist, vol. 156, pp. 269-286.
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Muyzer, G, Yildirim, E, van Dongen, U, Kuhl, M & Thar, R 2005, 'Identification of 'Candidatus Thioturbo danicus,' Microaerophilic Bacterium That Builds Conspicuous Veils on Sulfidic Sediments', Applied and Environmental Microbiology, vol. 71, no. 12, pp. 8929-8933.
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Molecular analysis of bacteria enriched under in situ-like conditions and mechanically isolated by micromanipulation showed that a hitherto-uncultivated microaerophilic bacterium thriving in oxygen-sulfide counter-gradients (R. Thar and M. Kühl, Appl. Environ. Microbiol. 68:6310-6320, 2000) is affiliated with the {varepsilon}-subdivision of the Proteobacteria. The affiliation was confirmed by the use of whole-cell hybridization with newly designed specific oligonucleotide probes. The bacterium belongs to a new genus and received the provisional name "Candidatus Thioturbo danicus."
O'Meara, TJ, Sercombe, JK, Morgan, G, Reddel, HK, Xuan, W & Tovey, ER 2005, 'The reduction of rhinitis symptoms by nasal filters during natural exposure to ragweed and grass pollen', Allergy, vol. 60, no. 4, pp. 529-532.
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Oren, A, Pri-El, N, Shapiro, O & Siboni, N 2005, 'Gas vesicles isolated from Halobacterium cells by lysis in hypotonic solution are structurally weakened', FEMS MICROBIOLOGY LETTERS, vol. 252, no. 2, pp. 337-341.
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Petrášek, Z, Schmitt, FJ, Theiss, C, Huyer, J, Chen, M, Larkum, A, Eichler, HJ, Kemnitz, K & Eckert, HJ 2005, 'Excitation energy transfer from phycobiliprotein to chlorophyll d in intact cells of Acaryochloris marina studied by time- and wavelength-resolved fluorescence spectroscopy', Photochemical and Photobiological Sciences, vol. 4, no. 12, pp. 1016-1022.
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The fluorescence decay spectra and the excitation energy transfer from the phycobiliproteins (PBP) to the chlorophyll-antennae of intact cells of the chlorophyll (Chl) d-dominated cyanobacterium Acaryochloris marina were investigated at 298 and 77 K by time- and wavelength-correlated single photon counting fluorescence spectroscopy. At 298 K it was found that (i) the fluorescence dynamics in A. marina is characterized by two emission peaks located at about 650 and 725 nm, (ii) the intensity of the 650 nm fluorescence depends strongly on the excitation wavelength, being high upon excitation of phycobiliprotein (PBP) at 632 nm but virtually absent upon excitation of chlorophyll at 430 nm, (iii) the 650 nm fluorescence band decayed predominantly with a lifetime of 70 ± 20 ps, (iv) the 725 nm fluorescence, which was observed independent of the excitation wavelength, can be described by a three-exponential decay kinetics with lifetimes depending on the open or the closed state (F0 or Fm) of the reaction centre of Photosystem II (PS II). Based on the results of this study, it is inferred that the excitation energy transfer from phycobiliproteins to Chl d of PS II in A. marina occurs with a time constant of about 70 ps, which is about three times faster than the energy transfer from the phycobilisomes to PS II in the Chl a-containing cyanobacterium Synechococcus 6301 (C. W. Mullineaux and A. R. Holzwarth, Biochim. Biophys. Acta, 1991, 68-78, 1098). A similar fast PBP to Chl d excitation energy transfer was also observed at 77 K. At 77 K a small long-lived fluorescence decay component with a lifetime of 14 ns was observed in the 640-700 nm spectral range. However, it has a rather featureless spectrum, not typical for Chl a, and was only observed upon excitation at 400 nm but not upon excitation at 632 and 654 nm. Thus, this long-lived fluorescence component cannot be used as an indicator that the primary PS II donor of Acaryochloris marina contains Chl a. © The Royal Soc...
Ralph, PJ & Gademann, R 2005, 'Rapid light curves: A powerful tool to assess photosynthetic activity', Aquatic Botany, vol. 82, no. 3, pp. 222-237.
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Rapid light curves provide detailed information on the saturation characteristics of electron transport, as well as the overall photosynthetic performance of a plant. Rapid light curves were collected from samples of Zostera marina grown under low and hi
Ralph, PJ, Larkum, A & Kuehl, M 2005, 'Temporal patterns in effective quantum yield of individual zooxanthellae expelled during bleaching', Journal Of Experimental Marine Biology And Ecology, vol. 316, no. 1, pp. 17-28.
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Bleaching is a worldwide phenomenon affecting coral reefs. During elevated temperature and light conditions (bleaching), expelled zooxanthellae show distinct patterns in photosynthetic health. An innovative new device was used to collect individual expel
Ralph, PJ, Macinnis-Ng, CM & Frankart, C 2005, 'Fluorescence imaging application: effect of leaf age on seagrass photokinetics', Aquatic Botany, vol. 81, no. 1, pp. 69-84.
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We used the Imaging-PAM fluorometer to map spatial variability of photosynthesis in three seagrass species, Halophila ovalis, Zostera capricorni and Posidonia australis. Photosynthesis was described by relative photosynthetic rate (PS/50), effective quan
Ralph, PJ, McMinn, A, Ryan, KG & Ashworth, C 2005, 'Short-term effect of temperature on the photokinetics of microalgae from the surface layers of Antarctic pack ice', Journal Of Phycology, vol. 41, no. 4, pp. 763-769.
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Microalgae growing within brine channels (85 psu salinity) of the surface ice layers of Antarctic pack ice showed considerable photosynthetic tolerance to the extreme environmental condition. Brine microalgae exposed to temperatures above -5 degrees C an
Ralph, PJ, Schreiber, U, Gademann, R, Kuehl, M & Larkum, A 2005, 'Coral photobiology studied with a new imaging pulse amplitude modulated fluorometer', Journal Of Phycology, vol. 41, no. 2, pp. 335-342.
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A new high-resolution imaging fluorometer (Imaging-PAM) was used to identify heterogeneity of photosynthetic activity across the surface of corals. Three species were examined: Acropora nobilis Dana (branching), Goniastrea australiensis Edwards A Haime (
Rodriguez-Lanetty, M, Scaramuzzi, C, Quinnell, RG & Larkum, AWD 2005, 'Transport of symbiotic zooxanthellae in mesogleal canals of Zoanthus robustus?', Coral Reefs, vol. 24, no. 2, pp. 195-196.
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Seymour, JR, Seuront, L & Mitchell, JG 2005, 'Microscale and small scale temporal dynamics of a coastal planktonic microbial community', Marine Ecology Progress Series, vol. 300, pp. 21-37.
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The temporal dynamics of heterotrophic bacteria and Synechococcus-type cyanobacteria communities were studied in a coastal habitat characterised by strong hydrodynamic variability using 10 s (microscale) and 30 min (small-scale) sampling intervals. Flow cytometric analysis allowed for the discrimination of 3 populations of heterotrophic bacteria and the examination of the Synechococcus cell cycle. During the 11 h small-scale study, 2-fold changes in the total abundance of both the bacterial and Synechococcus communities were observed, and clear temporal patterns in the abundance, activity and cellular state of the 2 populations were evident. Cumulative sum analysis further revealed distinct periods and trends in the temporal dynamics of the bacterial and Synechococcus communities. Shifts in the abundance of all heterotrophic bacterial populations were significantly correlated to turbulent energy dissipation. No such correlation was evident for the Synechococcus population, which instead appeared to follow a diel cell cycle very similar in nature to patterns observed in other environments. In 2 microscale studies, conducted during dissimilar hydrodynamic conditions, approx. 2-fold shifts in the abundance of the bacterial and Synechococcus populations were also observed. Microscale temporal patterns were dominated by localised variability and the existence of hotspots in abundance and activity, although cumulative sum analysis also revealed more general trends, sometimes occurring over periods of several minutes.
Smith, DJ, Suggett, DJ & Baker, NR 2005, 'Is photoinhibition of zooxanthellae photosynthesis the primary cause of thermal bleaching in corals?', Global Change Biology, vol. 11, no. 1, pp. 1-11.
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The bleaching of corals in response to increases in temperature has resulted in significant coral reef degradation in many tropical marine ecosystems. This bleaching has frequently been attributed to photoinhibition of photosynthetic electron transport a
Steunou, AS, Bateson, MM, Cohan, FM, Grossman, AR, Khuri, N, Ward, DM, Kuhl, M, Heidelberg, J & Bhaya, D 2005, 'THERMOPHILIC, MAT-DWELLING CYANOBACTERIAL STRAINS AND CONTROL OF METABOLISM', PHYCOLOGIA, vol. 44, no. 4, pp. 40-40.
Thar, R & Kuhl, M 2005, 'Complex pattern formation of marine gradient bacteria explained by a simple computer model', FEMS MICROBIOLOGY LETTERS, vol. 246, no. 1, pp. 75-79.
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Trapido-Rosenthal, H, Zielke, S, Owen, R, Buxton, LJ, Boeing, B, Bhagooli, R & Archer, J 2005, 'Increased zooxanthellae nitric oxide synthase activity is associated with coral bleaching', Biological Bulletin, vol. 208, no. 1, pp. 3-6.
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Coral bleaching, the breakdown of the symbiotic relationship between host corals and their photosynthetic dinoflagellate endosymbionts, is a phenomenon of major ecological significance. The cellular and molecular mechanisms underlying bleaching are poorl
Ulstrup, K, Hill, R & Ralph, PJ 2005, 'Photosynthetic impact of hypoxia on in hospite zooxanthellae in the scleractinian coral Pocillopora damicornis', Marine Ecology-Progress Series, vol. 286, pp. 125-132.
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Shallow water coral reefs may experience hypoxia under conditions of calm weather doldrums. Anaerobic responses of endosymbionts (i.e. zooxanthellae) within Pocillopora damicornis coral colonies were tested using both slow and fast chlorophyll a fluoresc
van der Meer, MT, Schouten, S, Bateson, MM, Nubel, U, Wieland, A, Kuhl, M, de Leeuw, JW, Damste, JS & Ward, DM 2005, 'Diel Variations in Carbon Metabolism by Green Nonsulfur-Like Bacteria in Alkaline Siliceous Hot Spring Microbial Mats from Yellowstone National Park', Applied and Environmental Microbiology, vol. 71, no. 7, pp. 3978-3986.
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Green nonsulfur-like bacteria (GNSLB) in hot spring microbial mats are thought to be mainly photoheterotrophic, using cyanobacterial metabolites as carbon sources. However, the stable carbon isotopic composition of typical Chloroflexus and Roseiflexus lipids suggests photoautotrophic metabolism of GNSLB. One possible explanation for this apparent discrepancy might be that GNSLB fix inorganic carbon only during certain times of the day. In order to study temporal variability in carbon metabolism by GNSLB, labeling experiments with [13C]bicarbonate, [14C]bicarbonate, and [13C]acetate were performed during different times of the day. [14C]bicarbonate labeling indicated that during the morning, incorporation of label was light dependent and that both cyanobacteria and GNSLB were involved in bicarbonate uptake. 13C-labeling experiments indicated that during the morning, GNSLB incorporated labeled bicarbonate at least to the same degree as cyanobacteria.
Wieland, A, Zopfi, J, Benthien, M & Kuhl, M 2005, 'Biogeochemistry of an Iron-Rich Hypersaline Microbial Mat (Camargue, France)', Microbial Ecology, vol. 49, no. 1, pp. 34-49.
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In situ microsensor measurements were combined with biogeochemical methods to determine oxygen, sulfur, and carbon cycling in microbial mats growing in a solar saltern (Salin-de-Giraud, France). Sulfate reduction rates closely followed the daily temperature changes and were highest during the day at 25C and lowest during the night at 11C, most probably fueled by direct substrate interactions between cyanobacteria and sulfate-reducing bacteria. Sulfate reduction was the major mineralization process during the night and the contribution of aerobic respiration to nighttime DIC production decreased. This decrease of aerobic respiration led to an increasing contribution of sulfide (and iron) oxidation to nighttime O2 consumption. A peak of elemental sulfur in a layer of high sulfate reduction at low sulfide concentration underneath the oxic zone indicated anoxygenic photosynthesis and/or sulfide oxidation by iron, which strongly contributed to sulfide consumption. We found a significant internal carbon cycling in the mat, and sulfate reduction directly supplied DIC for photosynthesis. The mats were characterized by a high iron content of 56 lmol Fe cm)3, and iron cycling strongly controlled the sulfur cycle in the mat. This included sulfide precipitation resulting in high FeS contents with depth, and reactions of iron oxides with sulfide, especially after sunset, leading to a pronounced gap between oxygen and sulfide gradients and an unusual persistence of a pH peak in the uppermost mat layer until midnight.