Collier, CJ, Lavery, PS, Ralph, PJ & Masini, RJ 2008, 'Physiological characteristics of the seagrass Posidonia sinuosa along a depth-related gradient of light availability', MARINE ECOLOGY PROGRESS SERIES, vol. 353, pp. 65-79.
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Physiological plasticity has the capacity to prolong seagrass survival under reduced light conditions. However, when light is attenuated across a depth gradient, the relative importance of this over other mechanisms for tolerating long-term light reduction (such as morphological adjustments and shoot loss) has been guestioned. This study aimed to describe a number of the physiological characteristics of Posidonia sinuosa Cambridge et Kuo along a depth-related gradient of light availability (1.6 to 9.0 m depth) and infer how these characteristics are important for the long-term maintenance of the meadow. Rapid light curve-derived parameters, light harvesting pigments, photoprotective pigments and nutrient and carbohydrate concentrations exhibited few differences among depth strata, but showed some (albeit limited) adjustment between the seasons. It was inferred that some physiological plasticity is possible in P. sinuosa but that differences in the depth-related gradient of long-term light availability were not sufficient to induce physiological differences, even at the depth limit. Shoot density reductions, which reduce the effects of self-shading, possibly offset depth-related light reductions. Because the physiological characteristics we examined did not explain the adaptations by P. sinuosa to the long-term gradient of light availability, they may not be useful indicators of long-term light reduction. © Inter-Research 2008.
Demir, E, Coyne, KJ, Doblin, MA, Handy, SM & Hutchins, DA 2008, 'Assessment of microzooplankton grazing on Heterosigma akashiwo using a species-specific approach combining quantitative real-time PCR (QPCR) and dilution methods', MICROBIAL ECOLOGY, vol. 55, no. 4, pp. 583-594.
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Delaware's Inland Bays (DIB) are subject to numerous mixed blooms of harmful raphidophytes each year, and Heterosigma akashiwo is one of the consistently occurring species. Often, Chattonella subsalsa, C. cf. verruculosa, and Fibrocapsa japonica co-occur
Demir, E, Coyne, KJ, Doblin, MA, Handy, SM & Hutchins, DA 2008, 'Assessment of microzooplankton grazing on Heterosigma akashiwo using a species-specific approach combining quantitative real-time PCR (QPCR) and dilution methods (vol 55, pg 583, 2008)', MICROBIAL ECOLOGY, vol. 55, no. 4, pp. 581-582.
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Dufresne, A, Ostrowski, M, Scanlan, DJ, Garczarek, L, Mazard, S, Palenik, BP, Paulsen, IT, Tandeau de Marsac, N, Wincker, P, Dossat, C, Ferriera, S, Johnson, J, Post, AF, Hess, WR & Partensky, F 2008, 'Unravelling the genomic mosaic of a ubiquitous genus of marine cyanobacteria', Genome Biology, vol. 9, no. 5, pp. R90-R90.
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Background: The picocyanobacterial genus Synechococcus occurs over wide oceanic expanses, having colonized most available niches in the photic zone. Large scale distribution patterns of the different Synechococcus clades (based on 16S rRNA gene markers) suggest the occurrence of two major lifestyles ('opportunists'/'specialists'), corresponding to two distinct broad habitats ('coastal'/'open ocean'). Yet, the genetic basis of niche partitioning is still poorly understood in this ecologically important group. Results: Here, we compare the genomes of 11 marine Synechococcus isolates, representing 10 distinct lineages. Phylogenies inferred from the core genome allowed us to refine the taxonomic relationships between clades by revealing a clear dichotomy within the main subcluster, reminiscent of the two aforementioned lifestyles. Genome size is strongly correlated with the cumulative lengths of hypervariable regions (or 'islands'). One of these, encompassing most genes encoding the light-harvesting phycobilisome rod complexes, is involved in adaptation to changes in light quality and has clearly been transferred between members of different Synechococcus lineages. Furthermore, we observed that two strains (RS9917 and WH5701) that have similar pigmentation and physiology have an unusually high number of genes in common, given their phylogenetic distance. Conclusion: We propose that while members of a given marine Synechococcus lineage may have the same broad geographical distribution, local niche occupancy is facilitated by lateral gene transfers, a process in which genomic islands play a key role as a repository for transferred genes. Our work also highlights the need for developing picocyanobacterial systematics based on genome-derived parameters combined with ecological and physiological data. © 2008 Dufresne et al.; licensee BioMed Central Ltd.
George, S, Tushar, KV, Unnikrishn, KP, Hashim, KM & Balachandr, I 2008, 'Hemidesmus indicus (L.) R. Br. A Review', Journal of Plant Sciences, vol. 3, no. 2, pp. 146-156.
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Hemidesmus indicus (L.) R. Br. (Periplocaceae) is being used widely in Ayurvedic medicine. The history of its medicinal importance dates back to ancient times. The present review deals with studies undertaken in various aspects of this plant in the areas of morphology, anatomy, pharmacology, chemistry and ethnobotany along with medicinal uses. © 2008 Academic Journals Inc.
Glibert, PM, Azanza, R, Burford, M, Furuya, K, Abal, E, Al-Azri, A, Al-Yamani, F, Andersen, P, Anderson, DM, Beardall, J, Berg, GM, Brand, L, Bronk, D, Brookes, J, Burkholder, JM, Cembella, A, Cochlan, WP, Collier, JL, Collos, Y, Diaz, R, Doblin, M, Drennen, T, Dyhrman, S, Fukuyo, Y, Furnas, M, Galloway, J, Graneli, E, Ha, DV, Hallegraeff, G, Harrison, J, Harrison, PJ, Heil, CA, Heimann, K, Howarth, R, Jauzein, C, Kana, AA, Kana, TM, Kim, H, Kudela, R, Legrand, C, Mallin, M, Mulholland, M, Murray, S, O'Neil, J, Pitcher, G, Qi, Y, Rabalais, N, Raine, R, Seitzinger, S, Salomon, PS, Solomon, C, Stoecker, DK, Usup, G, Wilson, J, Yin, K, Zhou, M & Zhu, M 2008, 'Ocean urea fertilization for carbon credits poses high ecological risks', MARINE POLLUTION BULLETIN, vol. 56, no. 6, pp. 1049-1056.
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The proposed plan for enrichment of the Sulu Sea, Philippines, a region of rich marine biodiversity, with thousands of tonnes of urea in order to stimulate algal blooms and sequester carbon is flawed for multiple reasons. Urea is preferentially used as a nitrogen source by some cyanobacteria and dinoflagellates, many of which are neutrally or positively buoyant. Biological pumps to the deep sea are classically leaky, and the inefficient burial of new biomass makes the estimation of a net loss of carbon from the atmosphere questionable at best. The potential for growth of toxic dinoflagellates is also high, as many grow well on urea and some even increase their toxicity when grown on urea. Many toxic dinoflagellates form cysts which can settle to the sediment and germinate in subsequent years, forming new blooms even without further fertilization. If large-scale blooms do occur, it is likely that they will contribute to hypoxia in the bottom waters upon decomposition. Lastly, urea production requires fossil fuel usage, further limiting the potential for net carbon sequestration. The environmental and economic impacts are potentially great and need to be rigorously assessed. © 2008 Elsevier Ltd. All rights reserved.
Harel, M, Ben-Dov, E, Rasoulouniriana, D, Siboni, N, Kramarsky-Winter, E, Loya, Y, Barak, Z, Wiesman, Z & Kushmaro, A 2008, 'A new Thraustochytrid, strain Fng1, isolated from the surface mucus of the hermatypic coral Fungia granulosa', FEMS MICROBIOLOGY ECOLOGY, vol. 64, no. 3, pp. 378-387.
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Hennige, SJ, Smith, DJ, Perkins, R, Consalvey, M, Paterson, DM & Suggett, DJ 2008, 'Photoacclimation, growth and distribution of massive coral species in clear and turbid waters', Marine Ecology Progress Series, vol. 369, pp. 77-88.
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Massive coral species play a key role in coral reef ecosystems, adding significantly to physical integrity, long term stability and reef biodiversity. This study coupled the assessment of the distribution and abundance of 4 dominant massive coral species, Diploastrea heliopora, Favia speciosa, F. matthaii and Porites lutea, with investigations into species-specific photoacclimatory responses within the Wakatobi Marine National Park of southeast Sulawesi, Indonesia, to determine the potential of photoacclimation to be a driver of biological success. For this, rapid light curves using pulse amplitude modulated (PAM) chlorophyll a fluorescence techniques were employed with additional manipulations to circumvent differences of light quality and absorption between species and across environmental gradients. P. lutea was examined over a range of depths and sites to determine patterns of photoacclimation, and all 4 species were assessed at a single depth between sites for which long-term data for coral community structure and growth existed. Light availability was more highly constrained with depth than between sites; consequently, photoacclimation patterns for P. lutea appeared greater with depth than across environmental gradients. All 4 species were found to differentially modify the extent of non-photochemical quenching to maintain a constant photochemical operating efficiency (qP). Therefore, our results suggest that these massive corals photoacclimate to ensure a constant light-dependent rate of reduction of the plastoquinone pool across growth environments. © Inter-Research 2008.
Hill, R & Ralph, PJ 2008, 'Dark-induced reduction of the plastoquinone pool in zooxanthellae of scleractinian corals and implications for measurements of chlorophyll a fluorescence', SYMBIOSIS, vol. 46, no. 1, pp. 45-56.
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Fluorometric measurements of maximum quantum yield (Fv/F m) and fast induction curves (FICs) require coral samples to be dark-adapted (DA). Pathways causing dark-reduction of the plastoquinone (PQ) pool are shown here to be active in corals. Early morning sunlight and far-red light successfully increased Fv/Fm and lowered the O and J steps of FICs in corals that were darkened overnight. The thick-tissued massive coral, Cyphastrea serailia, was shown to be more prone to reduction of the PQ pool, with significant reductions in Fv/Fm occurring after 10 min of DA, and elevated J steps occurring within 200 s following a far-red flash. In thinner-tissued branching species, Pocillopora damicornis and Acropora nobilis, elevation of the J step also occurred within 200 s of DA, but a drop in Fv/Fm was only manifested after 30 min. Pre-exposure to far-red light is an effective and simple procedure to ensure determination of the true maximum quantum yield of Photosystem II (PSII) and accurate FICs which require a fully oxidised inter-system electron transport chain and open PSII reaction centres. ©2008 Balaban.
Hill, R & Ralph, PJ 2008, 'Impact of bleaching stress on the function of the oxygen evolving complex of zooxanthellae from scleractinian corals', JOURNAL OF PHYCOLOGY, vol. 44, no. 2, pp. 299-310.
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Global climate change is leading to the rise of ocean temperatures and is triggering mass coral bleaching events on reefs around the world. The expulsion of the symbiotic dinoflagellate algae is believed to occur as a result of damage to the photosynthetic apparatus of these symbionts, although the specific site of initial impact is yet to be conclusively resolved. Here, the sensitivity of the oxygen evolving complex (OEC) to bleaching stress was studied as well as its natural variation between seasons. The artificial electron donor, diphenyl carbazide (DPC), was added to cultured, freshly isolated and expelled (bleaching treatments only) zooxanthellae suspensions. Chl a fluorescence and oxygen production measurements showed that upon addition of DPC, no restoration of diminished photochemical efficiency occurred under control or bleaching conditions. This result was consistent between 12 h and 5 d bleaching treatments on Pocilloporadamicornis, indicating that the OEC is not the primary site of damage, and that zooxanthellae expulsion from the host is a nonselective process with respect to the functioning of the OEC. Further experiments measuring fast induction curves (FICs) revealed that in both summer and winter, the temperature when OEC function was lost occurred between 7°C and 14°C above the sea surface temperature. FIC and oxygen production measurements of P. damicornis during exposure to bleaching stress demonstrated that the thermotolerance of the OEC increased above the temperature of the bleaching treatment over a 4 h period. This finding indicates that the OEC has the capacity to acclimate between seasons and remains functional at temperatures well above bleaching thresholds. © 2008 Phycological Society of America.
Howe, CJ, Barbrook, AC, Nisbet, RER, Lockhart, PJ & Larkum, AWD 2008, 'The origin of plastids', PHILOSOPHICAL TRANSACTIONS OF THE ROYAL SOCIETY B-BIOLOGICAL SCIENCES, vol. 363, no. 1504, pp. 2675-2685.
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It is generally accepted that plastids first arose by acquisition of photosynthetic prokaryotic endosymbionts by non-photosynthetic eukaryotic hosts. It is also accepted that photosynthetic eukaryotes were acquired on several occasions as endosymbionts by non-photosynthetic eukaryote hosts to form secondary plastids. In some lineages, secondary plastids were lost and new symbionts were acquired, to form tertiary plastids. Most recent work has been interpreted to indicate that primary plastids arose only once, referred to as a 'monophyletic' origin. We critically assess the evidence for this. We argue that the combination of Ockham's razor and poor taxon sampling will bias studies in favour of monophyly. We discuss possible concerns in phylogenetic reconstruction from sequence data. We argue that improved understanding of lineage-specific substitution processes is needed to assess the reliability of sequence-based trees. Improved understanding of the timing of the radiation of present-day cyanobacteria is also needed. We suggest that acquisition of plastids is better described as the result of a process rather than something occurring at a discrete time, and describe the 'shopping bag' model of plastid origin. We argue that dinoflagellates and other lineages provide evidence in support of this. © 2008 The Royal Society.
Ismar, Matthews & Hauber 2008, 'Seaweed provisioning behaviour confers thermal benefit for nesting Australasian gannets (Morus serrator)', Behaviour, vol. 145, no. 12, pp. 1823-1837.
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Jimenez, IM, Kuehl, M, Larkum, AWD & Ralph, PJ 2008, 'Heat budget and thermal microenvironment of shallow-water corals: Do massive corals get warmer than branching corals?', LIMNOLOGY AND OCEANOGRAPHY, vol. 53, no. 4, pp. 1548-1561.
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Coral surface temperature was investigated with multiple temperature sensors mounted on hemispherical and branching corals under (a) artificial lighting and controlled flow; (b) natural sunlight and controlled flow; and (c) in situ conditions in a shallo
Kazandjian, A, Shepherd, VA, Rodriguez-Lanetty, M, Nordemeier, W, Larkum, AWD & Quinnell, RG 2008, 'Isolation of Symbiosomes and The Symbiosome Membrane Complex from The Zoanthid Zoanthus Robustus', Phycologia, vol. 47, no. 3, pp. 294-306.
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The zoanthid Zoanthus robustus was used as a model organism to develop procedures for isolating pure symbiosomes and symbiosome membranes. The symbiosome is comprised of a zooxanthella (Symbiodinium sp.) cell that divides rarely and is separated from the host gastrodermal cytoplasm by a symbiosome multimembrane complex. Devising a method to isolate membranes at the interface between the symbiotic partners is a critical first step in characterising the molecular components involved in the metabolic trafficking necessary to sustain an effective symbiosis. After zoanthid gastrodermal cells were extracted, symbiosomes were released by mechanical disruption, recovered by centrifugation, and then purified using discontinuous sucrose gradient centrifugation. The material forming the membrane complex around symbiosomes proved highly resistant to disruption. Methods used to dissociate this interface from symbionts included (1) Triton X-100 detergent solubilisation, (2) osmotic shock with mechanical disruption, and (3) vigorous mechanical disruptions, where powerful shearing forces were used, combined with a series of sucrose density gradient centrifugation steps. The lipophilic styryl fluorochrome FM 1-43, at a concentration of 30 μM, selectively labelled the symbiosome membrane complex, both for isolated symbiosomes and those in hospite. Other cell membranes, including plasma membranes, endoplasmic reticulum, tonoplast, and organelle membranes, were not visibly labelled at this concentration. The selective labelling of the symbiosome membrane complex remained stable even after long exposure times (3 h). At 30 μM concentration, FM 1-43 also labelled symbiosome membrane fragments isolated using methods (1), (2) and (3). Method (3) proved to be the most effective in producing a fraction enriched in FM-143-labelled membrane material, which we call a symbiosome membrane complex. Transmission electron microscopy, together with confocal and conventional epifluorescence microsco...
Kuehl, M, Holst, G, Larkum, AWD & Ralph, PJ 2008, 'Imaging of oxygen dynamics within the endolithic algal community of the massive coral Porites lobata', JOURNAL OF PHYCOLOGY, vol. 44, no. 3, pp. 541-550.
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We used transparent planar oxygen optodes and a luminescence lifetime imaging system to map (at a pixel resolution of <200 ?m) the two-dimensional distribution of O2 within the skeleton of a Porites lobata colony. The O2 distribution was closely correlated to the distribution of the predominant endolithic microalga, Ostreobium quekettii Bornet et Flahault that formed a distinct green band inside the skeleton. Oxygen production followed the outline of the Ostreobium band, and photosynthetic O2 production was detected at only 0.2 ?mol photons m-2 · s-1, while saturation occurred at ?37 ?mol photons m-2 · s-1. Oxygen levels varied from ?60% to 0% air saturation in the illuminated section of the coral skeleton in comparison to the darkened section. The O2 production within the Ostreobium band was lower in the region below the upward facing surface of the coral and elevated on the sides. Oxygen consumption in darkness was also greatest within the Ostreobium zone, as well as in the white skeleton zone immediately below the corallites. The rate of O2 depletion was not constant within zones and between zones, showing pronounced heterogeneity in endolithic respiration. When the coral was placed in darkness after a period of illumination, O2 levels declined by 50% within 20 min and approached steady-state after 4050 min in darkness. Our study demonstrates the use of an important new tool in endolith photobiology and presents the first data of spatially resolved O2 concentration and its correlation to the physical structures and specific zones responsible for O2 production and consumption within the coral skeleton.
Martyn, AJ, Larkum, AWD, McConchie, R & Offord, CA 2008, 'Photoinhibition and changes in pigments associated with bract browning in waratahs (Telopea spp., Proteaceae)', JOURNAL OF HORTICULTURAL SCIENCE & BIOTECHNOLOGY, vol. 83, no. 3, pp. 367-373.
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The relationship between chronic or long-term photoinhibition, pigment changes, and bract browning in 'Fire and Brimstone', 'Olympic Flame' and 'Wirrimbirra White' waratahs [Telopea speciosissima (Smith) R.Br.] was investigated. Plants were grown under full sun, or under 50% shade-cloth over 2 years, with photoinhibition and pigment changes measured in the bracts and leaves at three stages of floral development (tight bud, juvenile open bud, and mature flower). Photoinhibition of waratah bracts was reduced by shading when applied either from flower initiation in late Summer, or from bud expansion in late Winter, until flower maturity in Spring. Outer bracts showed photoinhibition from the tight bud stage of flower development, and inner bracts from the juvenile open stage, while leaves were not affected. Photoinhibition, measured as pre-dawn photochemical efficiency (PE; Fv/Fm), declined in proportion to bract browning. Bracts on waratah plants kept under shade maintained higher chlorophyll, carotenoid, and anthocyanin levels than bracts exposed to full sun, and thus had a more intense flower colour. A significant decrease in bract pigmentation, combined with photoinhibition, indicates that photodamage occurs in bracts exposed to full sun. Leaf browning did not occur, and waratah leaves maintained a higher chlorophyll concentration than bracts in both full sun and shade conditions. Protection from photoinhibition was correlated with the level of UV-absorbing pigments.
Nedbal, L, Trtílek, M, Červený, J, Komárek, O & Pakrasi, HB 2008, 'A photobioreactor system for precision cultivation of photoautotrophic microorganisms and for high‐content analysis of suspension dynamics', Biotechnology and Bioengineering, vol. 100, no. 5, pp. 902-910.
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AbstractSmall‐scale photobioreactors for cultivation of photoautotrophic microbes are required for precise characterization of the growth parameters of wild‐type and engineered strains of these organisms, for their screening, and for optimization of culture conditions. Here, we describe the design and use of a flat‐cuvette photobioreactor that allows accurate control of culture irradiance, temperature, pH, and gas composition combined with real‐time monitoring by a built‐in fluorometer and densitometer. The high‐power LED light source generates precise irradiance levels that are programmed by user‐designed protocols. The irradiance, temperature, and gas composition may be static or dynamically modulated, while optical density and pH may be stabilized in turbidostat and pH‐stat modes, respectively. We demonstrate that the instrument is able to detect minute variations of growth caused, for example, by sudden dilution or by circadian rhythms. The sensitivity of the instrument is sufficient to monitor suspension optical density as low as 10−2. This newly designed photobioreactor can significantly contribute to the study and use of photoautotrophic microbes in systems biology and biotechnology. Biotechnol. Bioeng. 2008;100: 902–910. © 2008 Wiley Periodicals, Inc.
Petrou, K, Doblin, MA, Smith, RA, Ralph, PJ, Shelly, K & Beardall, J 2008, 'State transitions and nonphotochemical quenching during a nutrient-induced fluorescence transient in phosphorus-starved Dunaliella tertiolecta', JOURNAL OF PHYCOLOGY, vol. 44, no. 5, pp. 1204-1211.
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Assessments of nutrient-limitation in microalgae using chl a fluorescence have revealed that nitrogen and phosphorus depletion can be detected as a change in chl a fluorescence signal when nutrient-starved algae are resupplied with the limiting nutrient. This photokinetic phenomenon is known as a nutrient-induced fluorescence transient, or NIFT. Cultures of the unicellular marine chlorophyte Dunaliella tertiolecta Butcher were grown under phosphate starvation to investigate the photophysiological mechanism behind the NIFT response. A combination of low temperature (77 K) fluorescence, photosynthetic inhibitors, and nonphotochemical quenching analyses were used to determine that the NIFT response is associated with changes in energy distribution between PSI and PSII and light-stress-induced nonphotochemical quenching (NPQ). Previous studies point to state transitions as the likely mechanism behind the NIFT response; however, our results show that state transitions are not solely responsible for this phenomenon. This study shows that an interaction of at least two physiological processes is involved in the rapid quenching of chl a fluorescence observed in P-starved D. tertiolecta: (1) state transitions to provide the nutrient-deficient cell with metabolic energy for inorganic phosphate (Pi)-uptake and (2) energy-dependent quenching to allow the nutrient-stressed cell to avoid photodamage from excess light energy during nutrient uptake. © 2008 Phycological Society of America.
Reddy, CRK, Gupta, MK, Mantri, VA & Jha, B 2008, 'Seaweed protoplasts: status, biotechnological perspectives and needs', Journal of Applied Phycology, vol. 20, no. 5, pp. 619-632.
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Reddy, CRK, Jha, B, Fujita, Y & Ohno, M 2008, 'Seaweed micropropagation techniques and their potentials: an overview', Journal of Applied Phycology, vol. 20, no. 5, pp. 609-617.
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Roff, G, Ulstrup, KE, Fine, M, Ralph, PJ & Hoegh-Guldberg, O 2008, 'Spatial heterogeneity of photosynthetic activity within diseased corals from the great barrier reef', JOURNAL OF PHYCOLOGY, vol. 44, no. 2, pp. 526-538.
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Morphological diagnosis and descriptions of seven disease-like syndromes affecting scleractinian corals were characterized from the southern Great Barrier Reef (GBR). Chl a fluorescence of PSII was measured using an Imaging-PAM (pulse amplitude modulated) fluorometer, enabling visualization of the two-dimensional variability in the photophysiology of endosymbiotic dinoflagellates (zooxanthellae) by measuring rapid light curves. Three of four syndromes associated with active tissue loss (type a) were spatially homogenous (white syndrome, brown band, and skeletal eroding band), with no impact on the photochemical function of zooxanthellae populations at or behind the lesion borders. However, a decline in maximum quantum yield (Fv/F m) and elevated levels of maximum nonphotochemical quenching (NPQmax) occurred in visually healthy tissue of black band disease adjacent to the lesion borders, possibly due to hypoxic conditions caused by the black band cyanobacterial mat. Two out of three syndromes associated with pathological change of intact tissue with no active tissue loss (type b) showed variable photophysiological responses (neoplasia and pigmentation response). Only the bleached foci associated with white patch syndrome appeared to impact primarily on the symbiotic dinoflagellates, as evidenced by declines in minimum fluorescence (F0) and maximum quantum yield (Fv/F m), with no indication of degeneration in the host tissues. Our results suggest that for the majority of coral syndromes from the GBR, pathogenesis occurs in the host tissue, while the impact on the zooxanthellae populations residing in affected corals is minimal. © 2008 Phycological Society of America.
Ross, ON, Moore, CM, Suggett, DJ, MacIntyre, HL & Geider, RJ 2008, 'A model of photosynthesis and photo‐protection based on reaction center damage and repair', Limnology and Oceanography, vol. 53, no. 5, pp. 1835-1852.
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Phytoplankton photosynthesis under the rapidly fluctuating irradiance which results from turbulent mixing through the vertical light gradient is poorly understood. Ship‐based measurements often apply the fast repetition rate fluorescence (FRRF) technique in situ or in vivo to gauge the physiological state of the phytoplankton community and infer some of the physical properties of the water column (such as mixing time scales). We describe the development and validation of a model of photosynthetic electron turnover at photosystemII with consideration of downstream limitation, based on the redox state of photosystem II. We also include empirical formulations for slower processes such as photo‐protection (from nonphotochemical quenching) and photo‐inhibition. By confronting the simple model with laboratory data for Dunaliella tertiolecta, we were able to refine the model so that it faithfully produced rates of photosynthetic electron transfer determined by FRR fluorescence. Further, we were able to validate the model estimates of linear photosynthetic electron transfer rates against completely independent measurements obtained using 14C‐bicarbonate assimilation in photosynthesis‐light curves.
Seymour, JR, Ahmed, T, Marcos & Stocker, R 2008, 'A microfluidic chemotaxis assay to study microbial behavior in diffusing nutrient patches', LIMNOLOGY AND OCEANOGRAPHY-METHODS, vol. 6, pp. 477-488.
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The nutrient environment experienced by planktonic microorganisms is patchy at spatiotemporal scales commensurate with their motility and the efficiency with which chemotactic microbes can exploit this heterogeneous seascape influences trophodynamics and nutrient cycling rates in aquatic environments.
Seymour, JR, Seuront, L, Doubell, MJ & Mitchell, JG 2008, 'Mesoscale and microscale spatial variability of bacteria and viruses during a Phaeocystis globosa bloom in the Eastern English Channel', ESTUARINE COASTAL AND SHELF SCIENCE, vol. 80, no. 4, pp. 589-597.
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Sampling was conducted within inshore and offshore sites, characterized by highly dissimilar hydrodynamic and hydrobiological conditions, in the Eastern English Channel. The eutrophic inshore site was dominated by the influence of a dense bloom of the Prymnesiophyceae phytoplankton species Phaeocystis globosa, while the offshore site was characterized by more oceanic conditions. Within each site the microscale distributions of chlorophyll a and several flow cytometrically-defined subpopulations of heterotrophic bacteria and viruses were measured at a spatial resolution of 5 cm. The inshore site was characterized by comparatively high levels of microscale spatial variability, with concentrations of chlorophyll a, heterotrophic bacteria, and viruses varying by 8, 11 and 3.5-fold respectively across distances of several centimeters. Within the offshore site, microscale distributions of chlorophyll a and bacteria were markedly less variable than within the inshore site, although viruses exhibited slightly higher levels of heterogeneity. Significant mesoscale variability was also observed when mean microbial parameters were compared between the inshore and offshore sites. However, when the extent of change (max/min and coefficient of variation) was compared between meso- and microscales, the variability observed at the microscale, particularly in the inshore site, was substantially greater. This pattern suggests that microscale processes associated with Phaeocystis globosa bloom dynamics can generate heterogeneity amongst microbial communities to a greater degree than large scale oceanographic discontinuities.
Siboni, N, Ben Dov E, Sivan A & Kushmaro A 2008, 'Coral-associated ammonium oxidizing crenarchaeota and their role in the coral holobiont nitrogen cycle', Coral Reef Symp, Ft. Lauderdale, Florida, 7-11 July, vol. Session number 8.
Siboni, N, Ben-Dov, E, Sivan, A & Kushmaro, A 2008, 'Global distribution and diversity of coral-associated Archaea and their possible role in the coral holobiont nitrogen cycle', ENVIRONMENTAL MICROBIOLOGY, vol. 10, no. 11, pp. 2979-2990.
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Diversity, distribution and genetic comparison of Archaea associated with the surface mucus of corals from three genera, namely Acanthastrea sp., Favia sp. and Fungia sp., from the Gulf of Eilat, Israel and from Heron Island, Australia were studied. Sequencing of the 16S rRNA gene of the coral-associated Archaea revealed dominance of Crenarchaeota (79%, on average). In this phylum, 87% of the sequences were similar (≥ 97%) to the Thermoprotei, with 76% of these being similar (≥ 97%) to the ammonium oxidizer, Nitrosopumilus maritimus. Most of the coral-associated euryarchaeotal sequences (69%) were related to marine group II, while other euryarchaeotal clades were found to be related to anaerobic methanotrophs (8%), anaerobic nitrate reducers (i.e. denitrification, 15%) and marine group III (8%). Most of the crenarchaeotal and euryarchaeotal coral-associated 16S rRNA gene sequences from Heron Island (61%) and from the Gulf of Eilat (71%) were closely related (≥ 97%) to sequences previously derived from corals from the Virgin Islands. Analysis of archaeal amoA sequences obtained from the fungiid coral, Fungia granulosa, divided into three clades, all related to archaeal sequences previously obtained from the marine environment. These sequences were distantly related to amoA sequences previously found in association with other coral species. Preliminary experiments suggest that there is active oxidation of ammonia to nitrite in the mucus of F. granulosa. Thus, coral-associated Archaea may contribute to nitrogen recycling in the holobiont, presumably by acting as a nutritional sink for excess ammonium trapped in the mucus layer, through nitrification and denitrification processes. © 2008 The Authors.
Stocker, R, Seymour, JR, Samadani, A, Hunt, DE & Polz, MF 2008, 'Rapid chemotactic response enables marine bacteria to exploit ephemeral microscale nutrient patches', PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, vol. 105, no. 11, pp. 4209-4214.
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Because ocean water is typically resource-poor, bacteria may gain significant growth advantages if they can exploit the ephemeral nutrient patches originating from numerous, small sources. Although this interaction has been proposed to enhance biogeochemical transformation rates in the ocean, it remains questionable whether bacteria are able to efficiently use patches before physical mechanisms dissipate them. Here we show that the rapid chemotactic response of the marine bacterium Pseudoalteromonas haloplanktis substantially enhances its ability to exploit nutrient patches before they dissipate. We investigated two types of patches important in the ocean: nutrient pulses and nutrient plumes, generated for example from lysed algae and sinking organic particles, respectively. We used microfluidic devices to create patches with environmentally realistic dimensions and dynamics. The accumulation of P. haloplanktis in response to a nutrient pulse led to formation of bacterial hot spots within tens of seconds, resulting in a 10-fold higher nutrient exposure for the fastest 20% of the population compared with nonmotile cells. Moreover, the chemotactic response of P. haloplanktis was >10 times faster than the classic chemotaxis model Escherichia coli, leading to twice the nutrient exposure. We demonstrate that such rapid response allows P. haloplanktis to colonize nutrient plumes for realistic particle sinking speeds, with up to a 4-fold nutrient exposure compared with nonmotile cells. These results suggest that chemotactic swimming strategies of marine bacteria in patchy nutrient seascapes exert strong influence on carbon turnover rates by triggering the formation of microscale hot spots of bacterial productivity. © 2008 by The National Academy of Sciences of the USA.
Suggett, DJ, Warner, ME, Smith, DJ, Davey, P, Hennige, S & Baker, NR 2008, 'PHOTOSYNTHESIS AND PRODUCTION OF HYDROGEN PEROXIDE BY SYMBIODINIUM (PYRRHOPHYTA) PHYLOTYPES WITH DIFFERENT THERMAL TOLERANCES1', Journal of Phycology, vol. 44, no. 4, pp. 948-956.
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Occurrences whereby cnidaria lose their symbiotic dinoflagellate microalgae (Symbiodinium spp.) are increasing in frequency and intensity. These so‐called bleaching events are most often related to an increase in water temperature, which is thought to limit certain Symbiodinium phylotypes from effectively dissipating absorbed excitation energy that is otherwise used for photochemistry. Here, we examined photosynthetic characteristics and hydrogen peroxide (H2O2) production, a possible signal involved in bleaching, from two Symbiodinium types (a thermally “tolerant” A1 and “sensitive” B1) representative of cnidaria–Symbiodinium symbioses of reef‐building Caribbean corals. Under steady‐state growth at 26°C, a higher efficiency of PSII photochemistry, rate of electron turnover, and rate of O2 production were observed for type A1 than for B1. The two types responded very differently to a period of elevated temperature (32°C): type A1 increased light‐driven O2 consumption but not the amount of H2O2 produced; in contrast, type B1 increased the amount of H2O2 produced without an increase in light‐driven O2 consumption. Therefore, our results are consistent with previous suggestions that the thermal tolerance of Symbiodinium is related to adaptive constraints associated with photosynthesis and that sensitive phylotypes are more prone to H2O2 production. Understanding these adaptive differences in the genus Symbiodinium will be crucial if we are to interpret the response of symbiotic associations, including reef‐building corals, to environmental change.
Ulstrup, KE, Hill, R, van Oppen, MJH, Larkum, AWD & Ralph, PJ 2008, 'Seasonal variation in the photo-physiology of homogeneous and heterogeneous Symbiodinium consortia in two scleractinian corals', MARINE ECOLOGY PROGRESS SERIES, vol. 361, pp. 139-150.
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Seasonal variation in the composition of the algal endosymbiont community and photophysiology was determined in the corals Pocillopora damicornis,w hich show high local fidelity to one symbiont type (Symbiodinium C1) and Acropora valida, with a mixed Symbiodinium synbiont community, compromising members of both clades A and C. The relative abundances of Symbiodinium types varied overtime. A significant decline in symbiont densities in both coral species during the summer of 2005 coincided with a NOAA 'hotspot' warning for Heron Island. This also coincided with a relayiove increase in the presence and dominance of clade A in A. valida particularl in sun-adapted surfaces.
Unnikrishnan, KP, Raja, S & Balachandran, I 2008, 'A reverse phase HPLC-UV and HPTLC methods for determination of plumbagin inPlumbago indicaandPlumbago zeylanica', Indian Journal of Pharmaceutical Sciences, vol. 70, no. 6, pp. 844-844.
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Zwirglmaier, K, Jardillier, L, Ostrowski, M, Mazard, S, Garczarek, L, Vaulot, D, Not, F, Massana, R, Ulloa, O & Scanlan, DJ 2008, 'Global phylogeography of marine Synechococcus and Prochlorococcus reveals a distinct partitioning of lineages among oceanic biomes', Environmental Microbiology, vol. 10, no. 1, pp. 147-161.
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SummaryMarine cyanobacteria of the genera Prochlorococcus and Synechococcus are important contributors to global primary production occupying a key position at the base of marine food webs. The genetically diverse nature of each genus is likely an important reason for their successful colonization of vast tracts of the world's oceans, a feature that has led to detailed analysis of the distribution of these genetic lineages at the local and ocean basin scale. Here, we extend these analyses to the global dimension, using new data from cruises in the Pacific, Indian and Arctic Oceans in combination with data from previous studies in the Atlantic Ocean, Arabian Sea, Red Sea and a circumnavigation of the southern hemisphere to form a data set which comprises most of the world's major ocean systems. We show that the distribution patterns of Prochlorococcus and Synechococcus lineages are remarkably similar in different ocean systems with comparable environmental conditions, but producing a strikingly different ‘signature’ in the four major ocean domains or biomes (the Polar Domain, Coastal Boundary Domain, Trade Winds Domain and Westerly Winds Domain). This clearly reiterates the idea of spatial partitioning of individual cyanobacterial lineages, but at the global scale.
