Al-Najjar, MA, de Beer, D, Jorgensen, BB, Kuhl, M & Polerecky, L 2010, 'Conversion and conservation of light energy in a photosynthetic microbial mat ecosystem', ISME Journal, vol. 4, no. 3, pp. 440-449.
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Here we present, to the best of our knowledge, the first balanced light energy budget for a benthic microbial mat ecosystem, and show how the budget and the spatial distribution of the local photosynthetic efficiencies within the euphotic zone depend on the absorbed irradiance (Jabs). Our approach uses microscale measurements of the rates of heat dissipation, gross photosynthesis and light absorption in the system, and a model describing light propagation and conversion in a scatteringabsorbing medium. The energy budget was dominated by heat dissipation on the expense of photosynthesis: in light-limiting conditions, 95.5% of the absorbed light energy dissipated as heat and 4.5% was channeled into photosynthesis. This energy disproportionation changed in favor of heat dissipation at increasing irradiance, with >99% of the absorbed light energy being dissipated as heat and <1% used by photosynthesis at Jabs>700?µmol?photon?m-2?s-1 (>150?J?m-2?s-1). Maximum photosynthetic efficiencies varied with depth in the euphotic zone between 0.014-0.047 O2 per photon. Owing to steep light gradients, photosynthetic efficiencies varied differently with increasing irradiances at different depths in the euphotic zone; for example, at Jabs>700?µmol?photon?m-2?s-1, they reached around 10% of the maximum values at depths 0-0.3?mm and progressively increased toward 100% below 0.3?mm. This study provides the base for addressing, in much more detail, the photobiology of densely populated photosynthetic systems with intense absorption and scattering. Furthermore, our analysis has promising applications in other areas of photosynthesis research, such as plant biology and biotechnology.
Amoroso, S, Clarke, RJ, Larkum, A & Quinnell, R 2010, 'Electrogenic plasma membrane H+-ATPase activity using voltage sensitive dyes', Journal of Bioenergetics and Biomembranes, vol. 42, no. 5, pp. 387-393.
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Fast responding voltage sensitive dyes, RH421 and di-4-ASPBS, were used to study the electrogenic properties of plant plasma membrane proton pumps on sealed plasma membrane vesicles extracted by two-phase partitioning from Beta vulgaris and Avena sativa cv Swan root material. Fluorescence spectroscopy in the presence of the dye RH421 (10.8 nM) was sufficiently sensitive to detect electrogenic activity of the extracted plant vesicles. The dye detection system could detect inhibition of electrogenic activity of vesicles by vanadate (75 μM) and stimulation by nigericin (0.5 μM). The newly developed dye di-4-ASPBS was less sensitive to detecting the electrogenic proton pump activity. This study represents an important innovation in plant biophysics as this class of fast responding voltage sensitive dyes have never to our knowledge been used to study electrogenic proton pump activity derived from plant membranes and represents a novel approach for carrying out such studies. © 2010 Springer Science+Business Media, LLC.
Andersen, SB, Vestergaard, ML, Ainsworth, TD, Hoegh-Guldberg, O & Kuhl, M 2010, 'Acute tissue death (white syndrome) affects the microenvironment of tabular Acropora corals', Aquatic Biology, vol. 10, no. 1, pp. 99-104.
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White syndrome (WS) is a collective term for coral diseases that cause acute tissue loss, resulting in apparently healthy tissue bordering on exposed skeleton. In this study, the microenvironmental condition and tissue structure of WS-affected tabular acroporid corals were assessed by O2 microelectrodes and histological techniques. The high spatial resolution of the microelectrode measurements enabled an evaluation of the extent of physiological changes at, and 2 cm away from, the WS border. Respiration of the coral host was decreased on the skeletonâtissue border but was comparable to that of healthy corals only 2 cm away from the border. Histological data, however, showed a decrease in mesogloea thickness on and 2 cm away from the WS border, which correlates with a previously observed allocation of photoassimilates away from the WS border. We suggest that there are colony-wide negative effects of WS which affect only the host physiology and, as disparate etiologies are evident in WS, these must be distinguished through the utilization of a multiple tool approach.
Ashworth, J, Taylor, GK, Havranek, JJ, Quadri, SA, Stoddard, BL & Baker, D 2010, 'Computational reprogramming of homing endonuclease specificity at multiple adjacent base pairs', NUCLEIC ACIDS RESEARCH, vol. 38, no. 16, pp. 5601-5608.
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Askaer, L, Elberling, B, Glud, RN, Kuhl, M, Lauritsen, FR & Joensen, HP 2010, 'Soil heterogeneity effects on O2 distribution and CH4 emissions from wetlands: In situ and mesocosm studies with planar O2 optodes and membrane inlet mass spectrometry', Soil Biology & Biochemistry, vol. 42, no. 12, pp. 2254-2265.
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The importance of soil heterogeneity for methane emission from a wetland soil is assessed by in situ point measurements of depth-specific O2 and CH4 concentrations and simultaneous soil CH4 fluxes at contrasting water levels. Profile measurements, and associated assumptions in their interpretation, were validated in a controlled mesocosm drainage and saturation experiment applying planar O2 optodes and membrane inlet mass spectrometry. Results show that peat soil is heterogeneous containing dynamic macropore systems created by both macrofauna and flora, which facilitate preferential flow of water, O2 and CH4 and vary temporally with changes in the moisture regime. The O2 content above the water table after drainage varied horizontally from 0 to 100% air saturation within few mm. Oxic zones were observed below the water level and anoxic zones were observed in layers above the water level in periods up to days after changes in the water level. This study shows that although water table position is a competent proxy of soil CH4 fluxes at larger spatio-temporal scales, it becomes inadequate at higher spatial resolution, i.e. at the scale of the soil pedon and below. High resolution O2 measurements using planar O2 optodes have great potential to enhance our understanding of the effect of the water table position on O2 dynamics on scales of several cm to mm in wetland soils.
Chaloub, RM, Reinert, F, Nassar, CAG, Fleury, BG, Mantuano, DG & Larkum, AWD 2010, 'Photosynthetic properties of three Brazilian seaweeds', Revista Brasileira de Botanica, vol. 33, no. 2, pp. 371-374.
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Photosynthetic performance of distinct marine macroalgae, Ulva fasciata Delile (green alga), Lobophora variegata (J. V. Lamouroux) Womersley ex E. C. Oliveira (brown alga), and Plocamium brasiliensis (Greville) M. A. Howe & W. R. Taylor (red alga), were compared using a pulse amplitude-modulated fluorometer. The maximum quantum yield (Fv/Fm) ranged from 0.80 to 0.51, and the lowest value was found in P. brasiliensis. Under 400 μmol photons m-2 s-1 irradiance, the highest value of photochemical quenching (qP = 0.92 ± 0.13) was observed for U. fasciata. The red alga P. brasiliensis dissipated high amounts of excitation energy (qN = 0.56 ± 0.09), resulting in relatively low values for the effective quantum yield of PS-II (0.23 ± 0.04), as well as for the relative electron transport rate (3.3 ± 0.7). The high photosynthetic potential found for U. fasciata partially explains the species ability for rapid growth and high productivity.
Craggs, RJ & Sutherland, DL 2010, 'Win-win – extracting energy from wastewater', Water and Atmosphere, vol. 1, no. 5.
Csaszar, N, Ralph, PJ, Frankham, R, Berkelmans, R & van Oppen, MJ 2010, 'Estimating the Potential for Adaptation of Corals to Climate Warming', PLoS ONE, vol. 5, no. 3, pp. 1-8.
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The persistence of tropical coral reefs is threatened by rapidly increasing climate warming, causing a functional breakdown of the obligate symbiosis between corals and their algal photosymbionts (Symbiodinium) through a process known as coral bleaching. Yet the potential of the coral-algal symbiosis to genetically adapt in an evolutionary sense to warming oceans is unknown. Using a quantitative genetics approach, we estimated the proportion of the variance in thermal tolerance traits that has a genetics basis (i.e. heritability) as a proxy for their adaptive potential in the widespread Indo-Pacific reef-building coral Acropora millepora. We chose two physiologically different populations that associate respectively with one thermotolerant (Symbiodinium clade D) and one less tolerant symbiont type (Symbiodinium C2). In both symbiont types, pulse amplitude modulated (PAM) fluorometry and high performance liquid chromatography (HPLC) analysis revealed significant heritabilities for traits related to both photosynthesis and photoprotective pigment profile. However, quantitative real-time polymerase chain reaction (qRT - PCR) assays showed a lack of heritability in both coral host populations for their own expression of fundamental stress genes. Coral colony growth, contributed to by both symbiotic partners, displayed heritability. High heritabilities for functional key traits of algal symbionts, along with their short clonal generation time and high population sizes allow for their rapid thermal adaptation. However, the low overall heritability of coral host traits, along with the corals' long generation time, raise concern about the timely adaptation of the coral-algal symbiosis in the face of continued rapid climate warming.
Doblin, MA, Murphy, KR & Ruiz, GM 2010, 'Thresholds for tracing ships' ballast water:an Australian case study', Marine Ecology Progress Series, vol. 408, pp. 19-32.
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To limit the spread of non-indigenous marine species, ships can be legally required to conduct ballast water exchange (BWE) prior to discharging ballast water. It has been proposed to verify BWE by measuring concentrations of coastal tracers in ballast tanks, which should track their removal. Using 3 Australian ports as case studies (Port Botany, Port Curtis and Port Phillip Bay), each representing a different BWE verification difficulty level, the spatial and temporal variability of chromophoric dissolved organic matter (CDOM) and 3 trace elements (manganese [Mn], barium [Ba] and phosphorus [P]), were measured to assess their utility as tracers of coastal (unexchanged) ballast water. CDOM fluorescence at λex/λem = 320/414 nm (C2*) and 370/494 nm (C3*) and Mn concentrations were significantly higher in ports than in the adjacent Tasman Sea, except near port entrances and at a few sites in Port Botany. Ba concentrations demonstrated the least power to discriminate coastal sources, but P easily discriminated water from mesotrophic Port Phillip Bay. In general, tracers showed greater variation between and within ports, rather than between seasons. Conservative BWE thresholds were calculated to be 1.6 quinine sulphate equivalents for C2*, 0.9 quinine sulphate equivalents for C3*, 1.4 μg lâ1 for Mn and 6.9 μg lâ1 for Ba. Overall, these thresholds would allow water sourced from eastern Australian ports to be identified as coastal at 92%, 69% and 74% of sites examined using C3*, Mn and Ba, respectively, requiring 71 ± 26%, 54 ± 40% and 59 ± 38% replacement with mid-ocean water to be within ocean baseline concentration ranges.
Exton, DA, Smith, DJ, McGenity, TJ, Steinke, M, Hills, AJ & Suggett, DJ 2010, 'Application of a Fast Isoprene Sensor (FIS) for measuring isoprene production from marine samples', Limnology And Oceanography-methods, vol. 8, pp. 185-195.
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Research into isoprene production from marine sources traditionally relies on gas chromatography techniques which are labor intensive, provide a slow sample turnover, and require significant method training. An alternative method is the use of a Fast Iso
Hennige, SJ, Smith, DJ, Walsh, S, McGinley, MP, Warner, ME & Suggett, DJ 2010, 'Acclimation and adaptation of scleractinian coral communities along environmental gradients within an Indonesian reef system', Journal Of Experimental Marine Biology And Ecology, vol. 391, no. 1-2, pp. 143-152.
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In 2007 and 2008, multiple sites were identified in the Wakatobi Marine National Park, South East Sulawesi, Indonesia, which each represented a point along a gradient of light quality, temperature and turbidity. This gradient included `optimal, intermediate and marginal sites, where conditions were close to the survival threshold limit for corals. Coral communities changed across this gradient from diverse, mixed growth form assemblages to specialised, massive growth form dominated communities. The massive coral Goniastrea aspera was the only species identified at the most marginal and optimal sites. Branching species Acropora formosa and Porites cylindrica were only identified at optimal sites. The in hospite Symbiodinium community also changed across the environmental gradient from members of the Symbiodinium clade C on optimal reefs (in branching and massive species) to clade D on marginal reefs (in massive species). Substantial variability in respiration and photosynthesis was observed in massive coral species under different environmental conditions, which suggests that all corals cannot be considered equal across environments. Studying present-day marginal environments is crucial to further understanding of future reef bio-diversity, functioning and accretion, and from work presented here, it is likely that as future climate change extends marginal reef range, branching coral diversity may decrease relative to massive, more resilient corals.
Herrera-Silveira, JA, Cebrian, J, Hauxwell, J, Ramirez-Ramirez, J & Ralph, PJ 2010, 'Evidence of negative impacts of ecological tourism on turtlegrass (Thalassia testudinum) beds in a marine protected area of the Mexican Caribbean', Aquatic Ecology, vol. 44, no. 1, pp. 23-31.
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Many marine protected areas (MPAs) have been established in recent years. Some MPAs are open to tourists to foster environmental education and generate revenue for the MPA. This has been coined âecological tourismâ. Here, we examine the impact of ecological tourism on turtlegrass (Thalassia testudinum) health in one area of the âCosta Occidental de Isla Mujeres, Punta Cancún y Punta Nizucâ MPA in the Mexican Caribbean. A heavily visited location was compared with an unvisited location. Turtlegrass leaves at the visited location were sparser, shorter, grew more slowly, and had more epiphytes than at the unvisited location. Vertical and horizontal rhizomes of turtlegrass also grew more slowly at the visited than at the unvisited location. There is reasonable evidence to suggest that the observed differences are likely due to the deleterious impacts of novice and careless snorkelers. If continuing, these impacts could cause severe degradation of the visited areas in this MPA and, thus, changes in management policies seem in order.
Kalaitzis, JA, Chau, R, Kohli, GS, Murray, SA & Neilan, BA 2010, 'Biosynthesis of toxic naturally-occurring seafood contaminants', Toxicon, vol. 56, no. 2, pp. 244-258.
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Outbreaks of human illness caused by the consumption of contaminated seafood, continues to be a major problem particularly for the shellfish industry. Toxins from marine, brackish and freshwater environments, which are often produced as a result of harmful algal blooms, have been implicated as the causative agents of these poisonings. Commonly, poisoning events have been grouped into one of six classes, Paralytic Shellfish Poisoning (PSP), Diarrhetic Shellfish Poisoning (DSP), Neurotoxic Shellfish Poisoning (NSP), Ciguatera Fish Poisoning (CFP), Azaspiracid Shellfish Poisoning (AZP), and Amnesiac Shellfish Poisoning (ASP). The causative agents of these specific poisonings along with their biosyntheses are discussed in this review. The highly unusual and complex structures of most common seafood toxins have made them interesting targets for biosynthetic studies. Many of the toxins presented are biosynthesized via complex pathways that have been elucidated either through isotope labelled precursor feeding studies and/or characteriza- tion of the genes encoding the producing organisms biosynthetic machinery. Feeding studies key to our understanding of a particular toxins biosynthesis, such as the incor- poration of unusual precursors, as well as unique biosynthetic pathways and rare chemical mechanisms involved in the assembly process are highlighted. More recently, however, modern genomics-based techniques have been used for the elucidation of biosynthetic pathways and these are presented in the context of polyketide, non-ribosomal peptide, and hybrid pathway derived, toxin assembly.
Khan, N-UH, Pandya, N, Kumar, M, Bera, PK, Kureshy, RI, Abdi, SHR & Bajaj, HC 2010, 'Influence of chirality using Mn(III) salen complexes on DNA binding and antioxidant activity', ORGANIC & BIOMOLECULAR CHEMISTRY, vol. 8, no. 19, pp. 4297-4307.
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Korecko, J, Jirka, V, Sourek, B & Cerveny, J 2010, 'Module greenhouse with high efficiency of transformation of solar energy, utilizing active and passive glass optical rasters', SOLAR ENERGY, vol. 84, no. 10, pp. 1794-1808.
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Kumar, M, Gupta, V, Kumari, P & Reddy, CRK 2010, 'Assesment of nutrient composition and antioxidant potential of seaweeds from Caulerpaceae.', Journal of Food Composition and Analysis, vol. 24, no. 2, pp. 270-278.
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Abstract
The proximate nutrient composition, mineral contents, enzymatic and non-enzymatic antioxidant potential of three Caulerpa species were investigated. All three species were high in ash (24.20–33.70%) and carbohydrate content (37.23–48.95%) on dry weight basis (DW). The lipid content ranged between 2.64 and 3.06% DW. The mineral contents varied marginally among the species but were in the order of Na > K > Ca > Mg. The Na/K ratio among the species varied from 1.80 to 2.55 and was lowest in C. scalpelliformis. A 10 g DW of Caulerpa powder contains 11–21% Fe, 52–60% Ca and 35–43% Mg, which is higher than the recommended daily allowance (RDA), compared with non-seafood. The percentage sum of PUFAs (C18:2, C18:3, C20:4 and C20:5) in total fatty acids was highest in both C. scalpelliformis (39.25%) and C. veravelensis (36.73%) while it was the lowest in C. racemosa (24.50%). The n−6/n−3 ratio among the species varied from 1.44 to 7.72 and remained within the prescribed WHO standards (<10). Further, the higher enzymatic dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) and non-enzymatic antioxidant potential of Caulerpa species found in the present study confirm their usefulness in terms of nutrients and antioxidants.
Kumar, M, Kumari, P, Gupta, V, Anisha, PA, Reddy, CRK & Jha, B 2010, 'Differential responses to cadmium induced oxidative stress in marine macroalga Ulva lactuca (Ulvales, Chlorophyta)', BIOMETALS, vol. 23, no. 2, pp. 315-325.
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Kumar, M, Kumari, P, Gupta, V, Reddy, CRK & Jha, B 2010, 'Biochemical responses of red alga Gracilaria corticata (Gracilariales, Rhodophyta) to salinity induced oxidative stress', JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY, vol. 391, no. 1-2, pp. 27-34.
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Kumari, P, Kumar, M, Gupta, V, Reddy, CRK & Jha, B 2010, 'Tropical marine macroalgae as potential sources of nutritionally important PUFAs', FOOD CHEMISTRY, vol. 120, no. 3, pp. 749-757.
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Larkum, AWD 2010, 'Limitations and prospects of natural photosynthesis for bioenergy production', Current Opinion in Biotechnology, vol. 21, no. 3, pp. 271-276.
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Solar energy is clearly a major future source of energy for humans. While solar photovoltaic and thermal harvesting are attractive there will be a need for biofuels to replace fossil fuels. Natural photosynthesis offers a means to do this, but photosynthesis is inherently inefficient. Terrestrial plants have already been used as a source of biofuels and this use will increase in the future, despite a number of attendant problems. Microalgae as a source of biofuels have to be technically proven and artificial photosynthesis/biohydrogen production lies further into the future. Consideration of these approaches must be weighed against (i) crop production in a hungry, as well as a fuel-hungry, world and (ii) the need to sustain biodiversity. © 2010 Elsevier Ltd.
Lavery, TJ, Roudnew, B, Gill, P, Seymour, JR, Seuront, L, Johnson, G, Mitchell, J & Smetacek, V 2010, 'Iron Defecation By Sperm Whales Stimulates Carbon Export In The Southern Ocean', Proceedings Of The Royal Society B-Biological Sciences, vol. 277, no. 1699, pp. 3527-3531.
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The iron-limited Southern Ocean plays an important role in regulating atmospheric CO2 levels. Marine mammal respiration has been proposed to decrease the efficiency of the Southern Ocean biological pump by returning photosynthetically fixed carbon to the
Lilley, R, Ralph, PJ & Larkum, A 2010, 'The determination of activity of the enzyme Rubisco in cell extracts of the dinoflagellate alga Symbiodinium sp. by manganese chemiluminescence and its response to short-term thermal stress of the alga', Plant Cell and Environment, vol. 33, no. 6, pp. 995-1004.
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The dinoflagellate alga Symbiodinium sp., living in symbiosis with corals, clams and other invertebrates, is a primary producer in coral reefs and other marine ecosystems. The function of the carbon-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) in dinoflagellates is difficult to study because its activity is rapidly lost after extraction from the cell. We report procedures for the extraction of Rubisco from Symbiodinium cells and for stable storage. We describe a continuous assay for Rubisco activity in these crude cell extracts using the Mn2+ chemiluminescence of Rubisco oxygenase. Chemiluminescence time courses exhibited initial transients resembling bacterial Form II Rubisco, followed by several minutes of linearly decreasing activity. The initial activity was determined from extrapolation of this linear section of the time course. The activity of fast-frozen cell extracts was stable at -80 °C and, after thawing and storage on ice, remained stable for up to 1 h before declining non-linearly. Crude cell extracts bound [14C] 2-carboxy-D-arabitinol 1,5-bisphosphate to a high molecular mass fraction separable by gel filtration chromatography. After pre-treatment of Symbiodinium cell cultures in darkness at temperatures above 30 °C, the extracted Rubisco activities decreased, with almost complete loss of activity above 36 °C. The implications for the sensitivity to elevated temperature of Symbiodinium photosynthesis are assessed.
McMinn, A, Pankowskii, A, Ashworth, C, Bhagooli, R, Ralph, PJ & Ryan, K 2010, 'In situ net primary productivity and photosynthesis of Antarctic sea ice algal, phytoplankton and benthic algal communities', Marine Biology, vol. 157, no. 6, pp. 1345-1356.
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Primary production at Antarctic coastal sites is contributed from sea ice algae, phytoplankton and benthic algae. Oxygen microelectrodes were used to estimate sea ice and benthic primary production at several sites around Casey, a coastal area in eastern Antarctica. Maximum oxygen export from sea ice was 0.95 mmol O2 m-2 h-1 (*11.7 mg C m-2 h-1) while from the sediment it was 6.08 mmol O2 m-2 h-1 (*70.8 mg C m-2 h-1). When the ice was present O2 export from the benthos was either low or negative. Sea ice algae assimilation rates were up to 3.77 mg C (mg Chl-a)-1 h-1 while those from the benthos were up to 1.53 mg C (mg Chl-a)-1 h-1. The contribution of the major components of primary productivity was assessed using fluorometric techniques. When the ice was present approximately 55â65% of total daily primary production occurred in the sea ice with the remainder unequally partitioned between the sediment and the water column. When the ice was absent, the benthos contributed nearly 90% of the primary production.
Nedbal, L, Cerveny, J, Keren, N & Kaplan, A 2010, 'Experimental validation of a nonequilibrium model of CO2 fluxes between gas, liquid medium, and algae in a flat-panel photobioreactor', JOURNAL OF INDUSTRIAL MICROBIOLOGY & BIOTECHNOLOGY, vol. 37, no. 12, pp. 1319-1326.
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Ostrowski, M, Mazard, S, Tetu, SG, Phillippy, K, Johnson, A, Palenik, B, Paulsen, IT & Scanlan, DJ 2010, 'PtrA is required for coordinate regulation of gene expression during phosphate stress in a marine Synechococcus', ISME JOURNAL, vol. 4, no. 7, pp. 908-921.
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Perinchery, SM, Kuzhiumparambil, U, Vemulpad, S & Goldys, EM 2010, 'The influence of indoxyl sulfate and ammonium on the autofluorescence of human urine', TALANTA, vol. 80, no. 3, pp. 1269-1276.
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Perinchery, SM, Kuzhiumparambil, U, Vemulpad, S & Goldys, EM 2010, 'The potential of autofluorescence spectroscopy to detect human urinary tract infection', TALANTA, vol. 82, no. 3, pp. 912-917.
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Petrou, K, Hill, R, Brown, CM, Campbell, DA, Doblin, MA & Ralph, PJ 2010, 'Rapid photoprotection in sea-ice diatoms from the East Antarctic pack ice', Limnology and Oceanography, vol. 55, no. 3, pp. 1400-1407.
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Photoinhibition and D1 protein re-synthesis were investigated in bottom-dwelling sea-ice microalgal communities from the East Antarctic pack ice during early spring. Bottom-dwelling sea-ice microalgal communities were dominated by diatoms that exhibited rapid photoprotection when exposed to a range of different light levels (10 µmol photons m-2 s-1, 50 µmol photons m-2 s-1, 100 µmol photons m-2 s-1, and 200 µmol photons m-2 s-1). Photosynthetic capacity of photosystem II (PSII) dropped significantly over 3 h under 200 µmol photons m-2 s-1, but largely recovered when placed in a low-light environment (10 µmol photons m-2 s-1) for an additional 3 h. PSII repair rates increased with increasing irradiance, and the D1-protein pool remained steady even under high light (200 µmol photons m-2 s-1). Sea-ice diatoms showed a low intrinsic susceptibility to photoinactivation of PSII across all the light treatments, and a strong and irradiance-dependent induction of nonphotochemical quenching, which did not depend upon chloroplast protein synthesis, was also seen. These highly plastic organisms, once thought to be adapted to shade, are in fact well equipped to withstand rapid and relatively large changes in light at low temperatures with minimal long-term effect on their photosynthetic machinery.
Ragni, M, Airs, R, Hennige, SJ, Suggett, DJ, Warner, ME & Geider, RJ 2010, 'PSII photoinhibition and photorepair in Symbiodinium (Pyrrhophyta) differs between thermally tolerant and sensitive phylotypes', Marine Ecology Progress Series, vol. 406, pp. 57-70.
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Cnidarians containing symbiotic microalgae often inhabit highly variable light environments where successful growth requires that, during transient (potentially stressful) periods of high light (HL), the microalgal cells invest energy in photoprotection to minimise photodamage, or allow for photodamage to occur and invest in photorepair; however, the relative contribution of photoprotection and photorepair remains uncharacterised. Here we determined the light dependence of Photosystem II (PSII) photoinhibition and photorepair in 2 phylotypes of Symbiodinium displaying different susceptibilities to thermal stress. Upon exposure to photon flux densities (PFDs) >500 µmol photons m2 s1 the thermally `sensitive Strain A1.1 displayed higher net photoinhibition, measured as a decrease in maximum PSII efficiency (Fv/Fm), than the thermally `tolerant Strain A1. In contrast, gross photoinhibition, assessed as the decline of Fv/Fm in the presence of an inhibitor of D1 protein synthesis, was similar in the 2 strains. Therefore, photorepair was considered to be the key mechanism minimising net photoinhibition in Strain A1. Consistent with this conclusion, the 2 strains displayed similar capacities for other mechanisms of avoiding photodamage, specifically, photochemical (qP) and non-photochemical (NPQ) excitation energy quenching. Measurements on Strain A1 grown under 2 PFDs (100 and 650 µmol photons m2 s1) revealed that photoacclimation to HL involved the upregulation of qP, which minimised gross photoinhibition by maintaining PSII in a more oxidised state. We conclude that both interspecific (e.g. phylotype diversity) and intraspecific (e.g. photoacclimation state) factors affect the susceptibility of Symbiodinium to light stress.
Raina, J, Dinsdale, EA, Willis, BL & Bourne, DG 2010, 'Do the organic sulfur compounds DMSP and DMS drive coral microbial associations?', Trends in Microbiology, vol. 18, no. 3, pp. 101-108.
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Dimethylsulfoniopropionate (DMSP) and dimethylsulfide (DMS) are key compounds in the global sulfur cycle. Moreover, DMS is particularly important in climate regulation owing to its role in cloud formation. Reef building corals are major contributors to the production of these two compounds and also form diverse and complex associations with bacteria, which are known to play a crucial role in the degradation of DMSP and DMS. Here, we highlight an extensive overlap between bacterial species implicated in DMSP/DMS degradation and those associated with corals, leading to the hypothesis that these two compounds play a major role in structuring coral-associated bacterial communities, with important consequences for coral health and the resilience of coral reefs. We also explore the publically available metagenome databases and show that genes implicated in DMSP metabolism are abundant in the viral component of coral-reef-derived metagenomes, indicating that viruses can act as a reservoir for such genes.
Rosic, NN, Pernice, M, Dunn, S, Dove, S & Hoegh-Guldberg, O 2010, 'Differential Regulation by Heat Stress of Novel Cytochrome P450 Genes from the Dinoflagellate Symbionts of Reef-Building Corals', APPLIED AND ENVIRONMENTAL MICROBIOLOGY, vol. 76, no. 9, pp. 2823-2829.
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Seery, CR & Ralph, PJ 2010, 'Ecological relevance of a chlorophyll a fluorescence ecotoxicological endpoint', Toxicological and Environmental Chemistry, vol. 92, no. 8, pp. 1529-1540.
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With the increasing use of new techniques to assess toxic stress and the effects of pollution, it is important to ensure that any âânewââ endpoint employed is able to demonstrate a level of eco-relevance. Though recent application of chlorophyll a fluorescence parameters to macroalgal bioassays has been successful, a level of eco-relevance for such use has not been experimentally shown. As such, this article presents a series of experiments designed to establish a link between fluorescence parameters and higher-level effects (supra-individual level). The results show that fluorescence parameters are capable of predicting germination success of macroalgal gametes and can do so much sooner than the actual event of germination. Furthermore, a decline in DF=F0m is shown to be strongly associated with a reduced germination success. Thus, a level of eco-relevance has been established for the fluorescence endpoint that is at least equal to that of the widely accepted germination-based macroalgal bioassays.
Seymour, JR, Ahmed, T, Durham, W & Stocker, R 2010, 'Chemotactic Response Of Marine Bacteria To The Extracellular Products Of Synechococcus And Prochlorococcus', Aquatic Microbial Ecology, vol. 59, no. 2, pp. 161-168.
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The cyanobacterial genera Prochlorococcus and Synechococcus are key phototrophic organisms in the open ocean, and ecological interactions between these groups and heterotrophic bacteria have fundamental importance for marine carbon and nutrient cycling.
Seymour, JR, Simo, R, Ahmed, T & Stocker, R 2010, 'Chemoattraction to Dimethylsulfoniopropionate in the marine microbial food web', Science, vol. 329, no. 5989, pp. 342-345.
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Phytoplankton-produced dimethylsulfoniopropionate (DMSP) provides underwater and atmospheric foraging cues for several species of marine invertebrates, fish, birds, and mammals. However, its role in the chemical ecology of marine planktonic microbes is largely unknown, and there is evidence for contradictory functions. By using microfluidics and image analysis of swimming behavior, we observed attraction toward microscale pulses of DMSP and related compounds among several motile strains of phytoplankton, heterotrophic bacteria, and bacterivore and herbivore microzooplankton. Because microbial DMSP cycling is the main natural source of cloud-forming sulfur aerosols, our results highlight how adaptations to microscale chemical seascapes shape planktonic food webs, while potentially influencing climate at the global scale.
Siboni, N, Rasoulouniriana, D, Ben-Dov, E, Kramarsky-Winter, E, Sivan, A, Loya, Y, Hoegh-Guldberg, O & Kushmaro, A 2010, 'Stramenopile Microorganisms Associated with the Massive Coral Favia sp.', JOURNAL OF EUKARYOTIC MICROBIOLOGY, vol. 57, no. 3, pp. 236-244.
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Spilling, K, Titelman, J, Greve, T & Kuhl, M 2010, 'Microsensor Measurements Of The External And Internal Microenvironment Of Fucus Vesiculosus (Phaeophyceae)', Journal of Phycology, vol. 46, no. 6, pp. 1350-1355.
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We investigated the O2, pH, and irradiance microenvironment in and around the tissue of the brown alga Fucus vesiculosus L. using microsensors. Microsensors are ideal tools for gaining new insights into what limits and controls macroalgal activity and growth at very fine spatial (<100 lm) and temporal (seconds) scales. This first microsensor investigation of a fucoid macroalga revealed differences in the microenvironment and metabolic activities at the level of different cell layers and thallus structures. F. vesiculosus responded quickly to rapid shifts in irradiance resulting in a highly dynamic microenvironment around and within its thallus. In combination with detailed morphological studies and molecular approaches, microsensors offer a promising toolbox to quantitatively describe structural and functional adaptations of macroalgae to environmental conditions, such as flow and light climate, as well as their physiological responses to environmental stressors.
Szabo, M, Premvardhan, L, Lepetit, B, Goss, R, Wilhelm, C & Garab, G 2010, 'Functional heterogeneity of the fucoxanthins and fucoxanthin-chlorophyll proteins in diatom cells revealed by their electrochromic response and fluorescence and linear dichroism spectra', Chemical Physics, vol. 373, no. 1-2, pp. 110-114.
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Electrochromic transient, liner dichroism and 77 K fluorescence excitation and emission spectra show that fucoxanthins and fucoxanthin-chlorophyll proteins exhibit functional heterogeneity in diatom cells.
Wright, JT, Byers, JE, Koukoumaftsis, L, Ralph, PJ & Gribben, PE 2010, 'Native species behaviour mitigates the impact of habitat-forming invasive seaweed', Oecologia, vol. 163, no. 2, pp. 527-534.
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Habitat-forming invasive species cause large, novel changes to the abiotic environment. These changes may elicit important behavioural responses in native fauna, yet little is known about mechanisms driving this behaviour and how such trait-mediated responses influence the fitness of native species. Low dissolved oxygen is a key abiotic change created by the habitat-forming invasive seaweed, Caulerpa taxifolia, which influences an important behavioural response (burrowing depth) in the native infaunal bivalve Anadara trapezia. In Caulerpa-colonised areas, Anadara often emerged completely from the sediment, and we experimentally demonstrate that water column hypoxia beneath the Caulerpa canopy is the mechanism instigating this pop-up behaviour. Importantly, pop-up in Caulerpa allowed similar survivorship to that in unvegetated sediment; however, when we prevented Anadara from popping-up, they suffered >50% mortality in just 1 month. Our findings not only highlight the substantial environmental alteration by Caulerpa, but also an important role for the behaviour of native species in mitigating the effects of habitat-forming invasive species.
Zhang, Y, Chen, M, Church, WB, Lau, KW, Larkum, AWD & Jermiin, LS 2010, 'The molecular structure of the IsiA-Photosystem I supercomplex, modelled from high-resolution, crystal structures of Photosystem I and the CP43 protein', Biochimica et Biophysica Acta - Bioenergetics, vol. 1797, no. 4, pp. 457-465.
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We present the molecular structure of the IsiA-Photosystem I (PSI) supercomplex, inferred from high-resolution, crystal structures of PSI and the CP43 protein. The structure of iron-stress-induced A protein (IsiA) is similar to that of CP43, albeit with the difference that IsiA is associated with 15 chlorophylls (Chls), one more than previously assumed. The membrane-spanning helices of IsiA contain hydrophilic residues many of which bind Chl. The optimal structure of the IsiA-PSI supercomplex was inferred by systematically rearranging the IsiA monomers and PSI trimer in relation to each other. For each of the 6,969,600 structural configurations considered, we counted the number of optimal Chl-Chl connections (i.e., cases where Chl-bound Mg atoms are ≤. 25. Å apart). Fifty of these configurations were found to have optimal energy-transfer potential. The 50 configurations could be divided into three variants; one of these, comprising 36 similar configurations, was found to be superior to the other configurations in terms of its potential to transfer excitation energy to the reaction centres under low-light conditions and its potential to dissipate excess energy under high-light conditions. Compared to the assumed model [Biochemistry 42 (2003) 3180-3188], the new Chl increases by 7% the ability of IsiA to harvest sunlight while the rearrangement of the constituent components of the IsiA-PSI supercomplex increases by 228% the energy-transfer potential. In conclusion, our model allows us to explain how the IsiA-PSI supercomplex may act as an efficient light-harvesting structure under low-light conditions and as an efficient dissipater of excess energy under high-light conditions. © 2009 Elsevier B.V.