Baines, SB, Fisher, NS, Doblin, MA & Cutter, GA 2001, 'Uptake of dissolved organic selenides by marine phytoplankton', LIMNOLOGY AND OCEANOGRAPHY, vol. 46, no. 8, pp. 1936-1944.
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Se is present in multiple oxidation states in nature, each of which has unique chemical and biological reactivities. As a consequence, the rate of Se incorporation into food webs or its role as either a limiting nutrient or a toxic substance is a functio
Barbrook, AC, Symington, H, Nisbet, RER, Larkum, A & Howe, CJ 2001, 'Organisation and expression of the plastid genome of the dinoflagellate Amphidinium operculatum', MOLECULAR GENETICS AND GENOMICS, vol. 266, no. 4, pp. 632-638.
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We show using PCR that psbC, atpA and petB genes are present in the plastid DNA minicircles from the dinoflagellate Amphidinium operculatum, extending the set of plastid genes identified from this organism. Unusually, the petB and atpA genes are located on the same minicircle. PCR using primers based on the "core" region round on all coding minicircles revealed the existence of a number of DNA minicircles with no apparent coding function. Northern analysis of total RNA from A. operculatum showed that the petB and atpA genes are represented on separate transcripts, despite being encoded in close proximity on the same minicircle. The possibility of transcript editing was investigated by RT-PCR, but psaA, psbA, psbB and atpB transcripts showed no evidence of editing, indicating that GUA can be used as an initiation codon in A. operculatum.
C., C-R, L., C & A., L 2001, 'Atmospheric dinitrogen fixation by benthic communities of Tikehau Lagoon (Tuamotu Archipelago, French Polynesia) and its contribution to benthic primary production', Marine Biology, vol. 139, no. 5, pp. 991-998.
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Acetylene reduction rates were measured in lagoonal sediments, cyanobacterial mats and limestone surfaces between 1991 and 1995 at many sites, depths and seasons; all the studied substrata contained cyanobacteria. The acetylene reduction/15N2 fixation ratio was measured for the different communities and varied between 1.8 and 4.8, depending on substratum. Fixation rates were 1.7 to 7 times higher during daylight compared to night-time rates. N2 fixation rates ranged from 0.4 to 3.9 mg N m-2 day-1 for the lagoonal sediment/mat communities, and the rate was about 2 mg N m-2 day-1 for the lagoonal limestone substrata. Total lagoonal benthic N2 fixation contributed 24.4% of the total nitrogen requirement for the benthic primary production of benthic communities of the lagoon. The input of N2 fixation by the microbial planktonic communities (including cyanobacteria) of the lagoon, which are highly productive, is unquantified but is likely to be large.
De Beer, D & Larkum, AWD 2001, 'Photosynthesis and calcification in the calcifying algae Halimeda discoidea studied with microsensors', Plant, Cell & Environment, vol. 24, no. 11, pp. 1209-1217.
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AbstractWith microsensors, we measured the steady‐state microprofiles of O2, pH and Ca2+ on the topside of young segments of Halimeda discoidea, as well as the surface dynamics upon light–dark shifts. The effect of several inhibitors was studied. The steady‐state measurements showed that under high light intensity, calcium and protons were taken up, while O2 was produced. In the dark, O2 was consumed, the pH decreased to below seawater level and Ca2+ uptake was reduced to 50%. At low light intensity (12 mmol photons m‐2 s‐1), Ca2+ efflux was observed. Upon light–dark shifts, a complicated pattern of both the pH and calcium surface dynamics was observed. Illumination caused an initial pH decrease, followed by a gradual pH increase: this indicated that the surface pH of H. discoidea is determined by more than one light‐induced process. When photosynthesis was inhibited by dichlorophenyl dimethyl urea (DCMU), a strong acidification was observed upon illumination. The nature and physiological function of this putative pump is not known. The calcium dynamics followed all pH dynamics closely, both in the presence and absence of DCMU. The Ca‐channel blockers verapamil and nifedipine had no effect on the Ca2+ dynamics and steady‐state profiles. Thus, in H. discoidea, calcification is not regulated by the alga, but is a consequence of pH increase during photosynthesis. Acetazolamide had no effect on photosynthesis, whereas ethoxyzolamide inhibited photosynthesis at higher light intensities. Therefore, all carbonic anhydrase activity is intracellular. Carbonic anhydrase is required to alleviate the CO2 limitation. Calc...
Koop, K, Booth, D, Broadbent, A, Brodie, J, Bucher, D, Capone, D, Coll, J, Dennison, W, Erdmann, M, Harrison, P, Hoegh-Guldberg, O, Hutchings, P, Jones, GB, Larkum, AWD, O'Neil, J, Steven, A, Tentori, E, Ward, S, Williamson, J & Yellowlees, D 2001, 'ENCORE: The Effect of Nutrient Enrichment on Coral Reefs. Synthesis of Results and Conclusions', Marine Pollution Bulletin, vol. 42, no. 2, pp. 91-120.
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Coral reef degradation resulting from nutrient enrichment of coastal waters is of increasing global concern. Although effects of nutrients on coral reef organisms have been demonstrated in the laboratory, there is little direct evidence of nutrient effects on coral reef biota in situ. The ENCORE experiment investigated responses of coral reef organisms and processes to controlled additions of dissolved inorganic nitrogen (N) and/or phosphorus (P) on an offshore reef (One Tree Island) at the southern end of the Great Barrier Reef, Australia. A multi-disciplinary team assessed a variety of factors focusing on nutrient dynamics and biotic responses. A controlled and replicated experiment was conducted over two years using twelve small patch reefs ponded at low tide by a coral rim. Treatments included three control reefs (no nutrient addition) and three+N reefs (NH4Cl added), three+P reefs (KH2PO4 added), and three+N+P reefs. Nutrients were added as pulses at each low tide (ca twice per day) by remotely operated units. There were two phases of nutrient additions. During the initial, low-loading phase of the experiment nutrient pulses (mean dose=11.5 μMNH4+; 2.3μMPO4-3) rapidly declined, reaching near-background levels (mean=0.9μMNH4+; 0.5μMPO4-3) within 2-3 h. A variety of biotic processes, assessed over a year during this initial nutrient loading phase, were not significantly affected, with the exception of coral reproduction, which was affected in all nutrient treatments. In Acropora longicyathus and A. aspera, fewer successfully developed embryos were formed, and in A. longicyathus fertilization rates and lipid levels decreased. In the second, high-loading, phase of ENCORE an increased nutrient dosage (mean dose=36.2 μMNH4+; 5.1μMPO4-3 declining to means of 11.3 μMNH4+ and 2.4μMPO4-3 at the end of low tide) was used for a further year, and a variety of significant biotic responses occurred. Encrusting algae incorporated virtually none of the added nutrie...
Larkum, AWD, Karge, M, Reifarth, F, Eckert, H-J, Post, A & Renger, G 2001, 'Effect of monochromatic UV-B radiation on electron transfer reactions of Photosystem II', Photosynthesis Research, vol. 68, no. 1, pp. 49-60.
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The adverse effect of low intensity, small band UV-B irradiation (λ=305±5 nm, I=300 mW m-2) on PS II has been studied by comparative measurements of laser flash-induced changes of the absorption at 325 nm, ΔA325(t), as an indicator of redox changes in QA, and of the relative fluorescence quantum yield, F(t)/Fo, in PS II membrane fragments. The properties of untreated control were compared with those of samples where the oxygen evolution rate under illumination with continuous saturating light was inhibited by up to 95%. The following results were obtained: a) the detectable initial amplitude (at a time resolution of 30 μs) of the 325 nm absorption changes, ΔA325, remained virtually invariant whereas the relaxation kinetics exhibit significant changes, b) the 300 μs kinetics of ΔA325 dominating the relaxation in UV-B treated samples was largely replaced by a 1.3 ms kinetics after addition of MnCl2, c) the extent of the flash induced rise of the relative fluorescence quantum yield was severely diminished in UV-B treated PS II membrane fragments but the relaxation kinetics remain virtually unaffected. Based on these results the water oxidizing complex (WOC) is inferred to be the primary target of UV-B impairment of PS II while the formation of the 'stable' radical pair P680+•QA-• is almost invariant to this UV-B treatment.
Ralph, PJ, Gademann, R & Larkum, AWD 2001, 'Zooxanthellae expelled from bleached corals at 33 degrees C are photosynthetically competent', MARINE ECOLOGY PROGRESS SERIES, vol. 220, pp. 163-168.
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While a number of factors have been linked to coral bleaching, such as high light, high temperature, low salinity, and UV exposure, the best explanation for recent coral bleaching events are small temperature excursions of 1 to 2°C above summer sea-surface temperatures in the tropics which induce the dinoflagellate symbionts (zooxanthellae) to be expelled from the host. The mechanism that triggers this expulsion of the algal symbionts is not resolved, but has been attributed to damage to the photosynthetic mechanism of the zooxanthellae. In the present investigation we addressed the question of whether such expelled zooxanthellae are indeed impaired irreversibly in their photosynthesis. We employed a Microscopy Pulse Amplitude-Modulated (PAM) fluorometer, by which individual zooxanthellae can be examined to study photosynthesis in zooxanthellae expelled when corals are subjected to a temperature of 33°C. We show that the expelled zooxanthellae from Cyphastrea serailia were largely unaffected in their photosynthesis and could be heated to 37°C before showing temperature-induced photosynthetic impairment. These results suggest strongly that the early events that trigger temperature-induced expulsion of zooxanthellae involve a dysfunction in the interaction of the zooxanthellae and the coral host tissue, and not a dysfunction in the zooxanthellae per se.
Ritchie, RJ, Trautman, DA & Larkum, AWD 2001, 'Phosphate limited cultures of the cyanobacterium Synechococcus are capable of very rapid, opportunistic uptake of phosphate', New Phytologist, vol. 152, no. 2, pp. 189-201.
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SummaryPhosphate uptake rates were measured in Synechococcus R‐2 incubated in artificial secondary‐ and tertiary‐treated sewage.Phosphate uptake was measured using chemical assay and 32P incorporation. Intracellular pH was measured using accumulation of 14C‐labelled weak acids and bases and membrane potentials using 86Rb+/valinomycin. Synechococcus cells are capable of very rapid, opportunistic uptake of phosphate (10–30 nmol m−2 s−1) even though net uptake by growing cultures was < 0.5 nmol m−2 s−1. Km and Vmax in the light were not significantly different at pHo 7.5 and 10. The mean Km values were 1.91 ± 0.41 mmol m−3 and 0.304 ± 0.055 mmol m−3 for P‐sufficient (secondary‐treated sewage) and P‐deficient (tertiary‐treated sewage) cells, respectively. The transport systems probably recognize both H2PO4− and HPO42−. Intracellular inorganic phosphate is +28 to +56 kJ mol−1 from electrochemical equilibrium. In P‐sufficient cells uptake is very slow in the dark (c. 0.1 nmol m−2 s−1) but phosphate‐starved cells can opportunistically take up P about 100 times faster.Two separate ATP‐driven phosphate uptake mechanisms (1 PO4 in per ATP) appear to be responsible for phosphate uptake by the cells. They have different Km va...
Runcie, JW & Larkum, AWD 2001, 'Estimating Internal Phosphorus Pools in Macroalgae Using Radioactive Phosphorus and Trichloroacetic Acid Extracts', Analytical Biochemistry, vol. 297, no. 2, pp. 191-192.
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Suggett, D, Kraay, G, Holligan, P, Davey, M, Aiken, J & Geider, R 2001, 'Assessment of photosynthesis in a spring cyanobacterial bloom by use of a fast repetition rate fluorometer', Limnology and Oceanography, vol. 46, no. 4, pp. 802-810.
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Estimates of gross primary production (GPP) based on fast repetition rate fluorometer (FRRF) measurements were compared with independent 14C and O2 at three stations during a spring bloom in the North Atlantic. A photosynthesis versus irradiance (P‐E) curve was constructed for each station from the observations of in situ photon efficiency of photosynthesis. This composite P‐E curve was compared with P‐E curves determined for discrete samples from 14C assimilation. Estimates of aChl and PmChl from the 14C‐uptake method were 1.5–2.5‐fold lower than those estimated from the FRRF data. Much of this discrepancy can be accounted for if 14C assimilation approximates net phytoplankton photosynthesis with use of a photosynthetic quotient of 1.4 mol O2 (mol CO2)−1. Photosynthetic oxygen consumption may have also contributed to the difference. In situ GPP was calculated from incident irradiance, light attenuation, light absorption by phytoplankton, and the light dependence of the in situ photon efficiency. This estimate of GPP was two times greater than net community photosynthesis determined from diel changes of in situ oxygen concentration. Thus, the in situ net O2 and in vitro 14C techniques yielded similar estimates of phytoplankton photosynthesis that were about twofold lower than the estimates of GPP provided by FRRF. Uncertainties in the FRRF technique associated with choosing an appropriate value of photosynthetic unit size and fitting a P‐E curve to the in situ measurements are discussed. Despite these uncertainties, the FRRF results were consistent with the independent estimates of phytoplankton productivity.
Laroussi, M, Dobbs, FC, Wei, Z, Doblin, M, Ball, L, Moreira, K, Dyer, FF & Richardson, JP 1970, 'Effects of excimer UV radiation on microorganisms', IEEE International Conference on Plasma Science.
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It is well known that under high pressure conditions, microdischarges in rare gases or rare gas/halogen mixtures produce excimers. Excimers do not possess a stable ground state and tend to decay rapidly, releasing in the process radiation in the VUV, UV, or even visible range. The radiation generated by excimer lamps is incoherent, but intense and spectrally selective. Therefore, excimer lamps have been used in numerous applications such as surface modification, paint curing, material deposition, and pollution abatement. In this paper, we report a series of experiments on the use of a Dielectric Barrier Discharge (DBD) based excimer UV lamp to decontaminate water (both fresh and salty). The lamp presents a large area with a cylindrical geometry, and is RF-driven. In our experimental setup, the lamp is immersed into about a half liter of water containing a pre-selected concentration of a specific microorganism. The volume of water is exposed to the UV radiation emanating from the lamp and samples are taken, at selected time intervals, for analysis. The microorganisms used in our experiments are Escherichia coli, Bacillus subtilis, and Salmonella typhimurium, all bacteria, and the dinoflagellate Gymnodinium catenatum. Kill curves showing viability versus treatment time will be presented. In addition, a characterization of the morphological changes of the treated cells will be attempted.
