Staff Publications

Staff Publications

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    'Staff publications' is the digital repository of Wageningen University & Research

    'Staff publications' contains references to publications authored by Wageningen University staff from 1976 onward.

    Publications authored by the staff of the Research Institutes are available from 1995 onwards.

    Full text documents are added when available. The database is updated daily and currently holds about 240,000 items, of which 72,000 in open access.

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    Combined Effect of Light and Temperature on the Production of Saxitoxins in Cylindrospermopsis raciborskii Strains
    Mesquita, Marcella C.B. ; Lürling, Miquel ; Dorr, Fabiane ; Pinto, Ernani ; Marinho, Marcelo M. - \ 2019
    Toxins 11 (2019)1. - ISSN 2072-6651 - 15 p.
    cyanobacteria - cyanotoxins - intraspecific variability - saxitoxins

    Cylindrospermopsis raciborskii is a potentially toxic freshwater cyanobacterium that can tolerate a wide range of light and temperature. Due to climatic changes, the interaction between light and temperature is studied in aquatic systems, but no study has addressed the effect of both variables on the saxitoxins production. This study evaluated the combined effect of light and temperature on saxitoxins production and cellular quota in C. raciborskii. Experiments were performed with three C. raciborskii strains in batch cultures under six light intensities (10, 40, 60, 100, 150, and 500 μmol of photons m-2 s-1) and four temperatures (15, 20, 25, and 30 °C). The growth of C. raciborskii strains was limited at lower temperatures and the maximum growth rates were obtained under higher light combined with temperatures equal or above 20 °C, depending on the strain. In general, growth was highest at 30 °C at the lower light intensities and equally high at 25 °C and 30 °C under higher light. Highest saxitoxins concentration and cell-quota occurred at 25 °C under high light intensities, but were much lower at 30 °C. Hence, increased temperatures combined with sufficient light will lead to higher C. raciborskii biomass, but blooms could become less toxic in tropical regions.

    Integrated Product Recovery Will Boost Industrial Cyanobacterial Processes
    Berg, Corjan van den; Eppink, Michel H.M. ; Wijffels, Rene H. - \ 2019
    Trends in Biotechnology 37 (2019)5. - ISSN 0167-7799 - p. 454 - 463.
    cyanobacteria - process integration - product recovery - separation

    Cyanobacteria promise to be an important industrial platform for the production of a variety of biobased products such as fuels, plastics, and isoprenoids. Recent advances in synthetic biology have resulted in various cyanobacterial strain improvements. Nevertheless, these new strains are still hampered by product inhibition, resulting in low volumetric productivities, product concentrations, and yields on light. To circumvent these issues, continuous product recovery will need to be applied, resulting in economically viable industrial processes. Optimal product recovery strategies can be developed by considering biological and separation process constraints as well as photobioreactor design. Integrated product recovery will be indispensable to bring the cyanobacterial cell factory to industrial scale.

    The unfulfilled promise of urban Lake Kleine Melanen (The Netherlands) : Diagnostics, experiment on reduction of sediment P-release and in-lake restoration
    Waajen, Guido ; Lürling, Miquel ; Sande, René van de - \ 2019
    Lake and Reservoir Management 35 (2019)1. - ISSN 1040-2381 - p. 8 - 24.
    Biomanipulation - cyanobacteria - eutrophication management - Phoslock - polyaluminumchloride - sediment capping - stormwater runoff

    Lake Kleine Melanen (The Netherlands) experienced cyanobacterial blooms during the summertime, causing public health risks, turbid water, and lack of macrophytes. To improve the situation, we determined the underlying causes of the poor water quality. Our diagnosis included the water and phosphorus (P) budget of the lake and showed the need for the reduction of both the external and internal P loads. The external P load (7.5 mg P/m2/d) exceeded the transition between the clear water state and the turbid state by 44–121%, mainly due to the discharges from the separated stormwater sewer system in the adjacent neighborhood. Due to political and financial considerations of the managing authorities, the restoration (2010–2012) was restricted to internal management. To reduce the high internal P load (3.8 mg P/m2/d), we tested 3 sediment capping options in an enclosure experiment, showing the best results when we combined sand capping with the P fixative Phoslock® and flocculant polyaluminumchloride. A 0.6–1.3 m thick layer of soft sediment was dredged from the lake. Thereafter, the sediment was capped with a 0.2 m thick layer of sand to which Phoslock® was added. Additional in-lake measures including fish removal and shoreline reconstruction were also conducted to support improvement. We compared water quality before (2008–2010) and after (2012–2014) interventions. Although the mean concentration of total P was reduced from 0.30 to 0.11 mg P/L, and cyanobacterial chlorophyll a from 52 to 6 μg/L, cyanobacterial blooms still occurred. For further water quality improvement, the reduction of the external P load caused by stormwater runoff is required.

    Cyanobacterial Blooms and Microcystins in Southern Vietnam
    Trung, Bui ; Dao, Thanh Son ; Faassen, Els ; Lürling, Miquel - \ 2018
    Toxins 10 (2018)11. - ISSN 2072-6651
    aquaculture - cyanobacteria - cyanotoxins - Mekong river

    Studies on cyanobacteria in Vietnam are limited and mainly restricted to large reservoirs. Cyanobacterial blooms in small water bodies may pose a health risk to local people. We sampled 17 water bodies in the vicinity of urban settlements throughout the Mekong basin and in southeast Vietnam. From these, 40 water samples were taken, 24 cyanobacterial strains were isolated and 129 fish, 68 snail, 7 shrimp, 4 clam, and 4 duck samples were analyzed for microcystins (MCs). MCs were detected up to 11,039 µg/L or to 4033 µg/g DW in water samples. MCs were detected in the viscera of the animals. MC-LR and MC-RR were most frequently detected, while MC-dmLR, MC-LW, and MC-LF were first recorded in Vietnam. Microcystis was the main potential toxin producer and the most common bloom-forming species. A potential health hazard was found in a duck⁻fish pond located in the catchment of DauTieng reservoir and in the DongNai river where raw water was collected for DongNai waterwork. The whole viscera of fish and snails must be completely removed during food processing. Cyanobacterial monitoring programs should be established to assess and minimize potential public health risks.

    Comparison of Protein Extracts from Various Unicellular Green Sources
    Teuling, Emma ; Wierenga, Peter A. ; Schrama, Johan W. ; Gruppen, Harry - \ 2017
    Journal of Agricultural and Food Chemistry 65 (2017)36. - ISSN 0021-8561 - p. 7989 - 8002.
    amino acid composition - carbohydrate composition - cyanobacteria - Microalgae - physicochemical properties - single-cell protein
    Photosynthetic unicellular organisms are considered as promising alternative protein sources. The aim of this study is to understand the extent to which these green sources differ with respect to their gross composition and how these differences affect the final protein isolate. Using mild isolation techniques, proteins were extracted and isolated from four different unicellular sources (Arthrospira (spirulina) maxima, Nannochloropsis gaditana, Tetraselmis impellucida, and Scenedesmus dimorphus). Despite differences in protein contents of the sources (27-62% w/w) and in protein extractability (17-74% w/w), final protein isolates were obtained that had similar protein contents (62-77% w/w) and protein yields (3-9% w/w). Protein solubility as a function of pH was different between the sources and in ionic strength dependency, especially at pH < 4.0. Overall, the characterization and extraction protocol used allows a relatively fast and well-described isolation of purified proteins from novel protein sources.
    Eco-engineering for clarity : clearing blue-green ponds and lakes in an urbanized area
    Waajen, Guido W.A.M. - \ 2017
    Wageningen University. Promotor(en): M. Scheffer, co-promotor(en): M.F.L.L.W. Lürling. - Wageningen : Wageningen University - ISBN 9789463431095 - 306
    ponds - lakes - ecological engineering - urban areas - cyanobacteria - eutrophication - water quality - water management - plassen - meren - natuurtechniek - stedelijke gebieden - cyanobacteriën - eutrofiëring - waterkwaliteit - waterbeheer

    Small lakes and ponds are common features in urban areas and they contribute to the quality of citizens’ life. A poor water quality, however, can easily give rise to nuisance. A major cause for a poor water quality is a high concentration of plant-nourishing nutrients, eutrophication. In (semi-)standing waters, eutrophication often results in a high biomass of blue-green algae (cyanobacteria), turbid water and the disappearance of submerged aquatic plants. The cyanobacterial blooms can be accompanied with fish kills due to anoxia, the development of unpleasant surface scums and malodors. As cyanobacteria can produce potent toxins, they impose a serious risk for citizens’ health, pets and wildlife. The cyanobacterial blooms hamper the anthropogenic use of the water and can have negative economic impacts. Water managers experience that the reduction of cyanobacterial nuisance is arduous. As long-term positive effects of management interventions are not often achieved, there is need for effective approaches.

    The objective of this study was to investigate the efficacy of promising methods to reduce cyanobacterial nuisance in city waters, targeting the clear water state and promoting the growth of aquatic plants. Various methods were tested, in the laboratory, in small and large compartments and were eventually applied in whole ponds and lakes. It is widely accepted that the reduction of nutrient inputs is essential for long-term positive effects. This study focused on the reduction of the input and the availability of the key-nutrient phosphorus. It was shown that cyanobacterial nuisance was wide spread in urban ponds and lakes in the Dutch province of North Brabant. The phosphorus inputs of four urban lakes in this province were addressed. The study lakes differed greatly in the phosphorus sources and loads, depending on site-specific characteristics. These differences affected the selection of measures. It was shown that in-lake measures were effective in realizing the long-term abatement of the cyanobacterial nuisance, provided the external phosphorus input was limited. If the external phosphorus input could not be limited sufficiently, in-lake measures did not result in the long-term reduction of cyanobacterial nuisance.

    To reduce the bioavailable phosphorus stock in the lake with in-lake measures, sediment capping with a phosphorus-binding agent (lanthanum-modified bentonite, LMB) can be effective and cheaper than sediment removal by dredging. The additional use of a flocculant may have added value and suppressed cyanobacterial blooms quickly and effectively. Aquatic plants and macroinvertebrates responded positively to the achieved improvement of the water quality. Accumulation of lanthanum was shown in aquatic plants and fish, following LMB exposure. No toxic effects of lanthanum from LMB were observed. Depending on site-specific characteristics, dredging or LMB did not suffice to limit the available phosphorus stock in the lake. For this situation, the additional capping of the sediment with sand was tested and subsequently applied in a lake. Management of the fish biomass and lake reconstruction can support rehabilitation. The results of this study underpin the importance of a site-specific diagnosis (water system analysis). The diagnosis clarifies the underlying causes of cyanobacterial nuisances and is essential for a site-specific tailored set of measures. This study showed that a site-specific set of measures reduced cyanobacterial nuisance effectively for a long term.

    As eutrophication control is not always feasible or might be effective only in the long run, curative measures are needed for symptom relief. Several curative end-of-pipe measures that are often suggested were evaluated: effective microorganisms (EM®), golden algae, plant extracts, ultrasound and artificial mixing of non-stratifying waters. No strong support for the efficacy of these measures could be shown. Next to the above mentioned application of flocculant, the use of freshwater quagga mussels is promising. The efficacy of the mussels was experimentally tested and it was shown that the introduction of mussels in a hypertrophic urban pond reduced the phytoplankton biomass, including cyanobacteria, and induced a clear water state. The quagga mussel is an invasive alien species and new introductions should be considered carefully.

    Based on the results from this study, the thesis provides a road map for water managers for the reduction of cyanobacterial nuisances in urban ponds and lakes.

    Further improvements in water quality of the Dutch Borderlakes : two types of clear states at different nutrient levels
    Noordhuis, Ruurd ; Zuidam, B.G. van; Peeters, E.T.H.M. ; Geest, G.J. van - \ 2016
    Aquatic Ecology 50 (2016)3. - ISSN 1386-2588 - p. 521 - 539.
    Abramis brama - Alternative stable states - Biomanipulation - Cyanobacteria - Dreissena - Macro-algae - Quagga Mussel - Regime shift - randmeren - mussels - algae - water quality - aquatic ecology - eutrophication - randmeren - abramis brama - mossels - cyanobacteriën - algen - waterkwaliteit - aquatische ecologie - eutrofiëring

    The Borderlakes are a chain of ten shallow, largely artificial, interconnected lakes in the Netherlands. The ecological recovery of the central Borderlakes (viz. lake Veluwe and Wolderwijd) has been well documented. These lakes shifted from a eutrophic, Planktothrix dominated state in the 1970s to a clear state in 1996. Around 2010, the formerly hypertrophic, southern Borderlake Eem also reached a clear state, but at considerably higher nutrient levels. In this paper, monitoring data are used to compare these changes and identify the differences in driving processes and their consequences. The 1996 shift in Lake Veluwe was linked to increased fishery for benthivorous Bream, followed and stabilized by increase in Zebra Mussels and charophytes. Nutrients in Lake Eem decreased as well and Planktothrix disappeared here too in 1996, despite relatively high TP concentrations which remained stable over time. The start of the change into the clear state in this case also involved a decrease in the Bream population, but with a stronger additional role for dreissenids, particularly of Quagga Mussels. Remaining blooms of cyanobacteria almost disappeared, but the current situation in Lake Eem represents a different type of clear water state than in the central Borderlakes. This type is characterized by the combination of a relatively high phosphorus load, intense dreissenid filtration and filamentous macro-algae instead of either blooms of cyanobacteria or dominance of charophytes. With the dominant role of the River Eem, the relatively short residence time and increasing difficulty to bring down nutrient loading any further, the stability of this clear state depends on high densities (and filtration rates) of dreissenids.

    Light harvesting, light adaptation and photoprotection in aquatic photosynthesis studies by time-resolved fluorescence spectroscopy
    Chukhutsina, V. - \ 2015
    Wageningen University. Promotor(en): Herbert van Amerongen. - Wageningen : Wageningen University - ISBN 9789462572454 - 190
    licht - adaptatie - bacillariophyta - cyanobacteriën - verdedigingsmechanismen - fotochemie - spectrofluorimetrie - light harvesting complexen - light - adaptation - bacillariophyta - cyanobacteria - defence mechanisms - photochemistry - spectrofluorimetry - light harvesting complexes

    Summary

    Aquatic photosynthetic organisms unavoidably experience light fluctuations that vary in amplitude, duration and origin, compromising their photosynthetic efficiency. Weather conditions and underwater flow cause continuous changes in irradiance to which the organisms have to adapt. Many light-adaptation strategies of photosynthetic organisms, such as light acclimation, photoprotection and state transitions are still not well understood. In this thesis, time-resolved fluorescence spectroscopy is used to obtain insight into the response of diatoms and cyanobacteria, both aquatic photosynthetic organisms, to changing light conditions.

    In chapter 2, photoacclimation (long-term acclimation to irradiance conditions) of the diatom Cyclotella meneghiniana is discussed. It is shown that the diatom cells fine-tune the amount of absorbed light energy by modifying their antenna size: cells grown in high light intensity have smaller antennas than those grown in low light. At the same time, the increase of growth light intensity leads to a decrease of the relative amount of photosystem I (PSI) as compared to PSII. Such a strategy might be beneficial for diatoms, since they are known to have an electron transfer cycle around PS II to release excess electrons produced in high light intensities. Besides discussing photoacclimation, we give a detailed description the fluorescence kinetics in C. meneghiniana. It is concluded that the diatom antenna, represented by light-harvesting fucoxanthin chlorophyll proteins (FCPs), transfer their excitation energy predominantly to PSII. FCPs associated with PSII are slightly richer in red-absorbing fucoxanthin than the FCPs associated with PSI, suggesting that PSII antennas (partly) constitute the antenna form FCPb (i.e. oligomeric antenna complexes).

    In chapter 3 the process of non-photochemical quenching (NPQ, thermal dissipation of excess absorbed light energy) of chlorophyll a fluorescence was studied in the same diatom species. Diatoms can rapidly switch on/off NPQ to respond to fast light-intensity changes in moving waters. They are capable to induce higher NPQ values than plants or other photosynthetic organisms. The reason for such high NPQ values, however, is not clear. We performed picosecond fluorescence measurements at 77K on cells locked in three different states: Besides using conventional unquenched and quenched states of the cells (in the absence and presence of the total NPQ component, respectively), we also performed measurements on the dark-adapted state directly following NPQ. In this state, diatoxantin (Dtx, a carotenoid related to NPQ), accumulated during the NPQ period and Dtx-related NPQ persists, while ΔpH-related NPQ has relaxed. In this way we revealed the following sequence of events during full development of NPQ. First, the pH gradient across the thylakoid membrane induces quenching of FCP trimers (FCPa complexes), while they are still part of PSII. This is followed by (partial) detachment of FCPa from PSII after which quenching persists. The pH gradient also causes the formation of Dtx, which leads to further quenching of isolated PSII cores and some aggregated FCPa. To summarize, quenching of PSII -both cores and complexes- and FCPa substantially contribute to NPQ in diatoms. The FCPb antenna form on the other hand does not contribute to the NPQ process.

    Certain aquatic photosynthetic organisms, such as cyanobacteria and green algae, can also cope with changing light conditions by dynamically varying the relative antenna size of PSI and of PSII. Consequently, a redistribution of light energy between the PSs is achieved. This phenomenon is called “state transitions”. It is known to be driven via a change in the redox status of electron carriers between PSII and PSI. In cyanobacteria, this redox change can be achieved via dark-light transitions. However, the cascade of microscopic events that lead to subsequent energy redistribution in cyanobacteria is still not completely clear. In chapter 4, a study on dark-light transitions using the cyanobacterium Synechocystis sp. PCC 6803 as a model organism is described. It is demonstrated that during dark to light transitions, there is mainly detachment of phycobilisomes (PBSs) (cyanobacterial antennas) from PSI, generally not followed by their attachment to PSII: only 15 % of the PBSs that detach from PSI actually move to PSII, while the major part remains detached from both PSs. We conclude that PSI-PSII-PBS megacomplexes, which were recently isolated using chemical cross-linking, are not involved in dark/light state transitions, suggesting that, if present, they are only transiently formed in cyanobacteria. To summarize, the findings presented in chapter 4 suggest that in cyanobacteria, unlike in green algae or higher plants, the main role of state transitions is to change the absorption cross-section of PSI, rather than that of PSII.

    In chapter 5, a study of the role of flv4-2 operon-encoded proteins in Synechocystis is described. Three genes are found in the operon: Flv4, Sll0218, and Flv2. Only recently flv4-2 operon-encoded proteins were found to constitute an additional photoprotective mechanism in a number of cyanobacteria by safeguarding PSII activity via an alternative electron chain. Its contribution becomes vital for the cells in high light and in air-level CO2, when the photosynthetic electron transport chain is over-reduced. It is demonstrated that deletion of the operon induces 20% PBS detachment. The reduced PSII dimer to monomer ratio, as a result of the absence of the small Sll0218 protein, favors a relative decrease of the PSII dimer content of about 20%, showing a direct correlation between PSII dimer destabilization and PBS detachment from reaction centers. On the other hand, the suggested binding of the Flv2/Flv4 heterodimer closely to the quinone B (QB) pocket in PSII increases the QB redox potential, thereby promoting forward electron transfer and increasing the charge separation rates in PSII. This activity of the Flv2/Flv4 heterodimer in combination with its earlier reported role as an electron acceptor in alternative electron chain provides more oxidized state of the PQ pool in high light and in air-level CO2.

    Beating the blues: Is there any music in fighting cyanobacteria with ultrasound?
    Lurling, M.F.L.L.W. ; Tolman, Y. - \ 2014
    Water Research 66 (2014). - ISSN 0043-1354 - p. 361 - 373.
    oppervlaktewater - cyanobacteriën - ultrageluid - waterkwaliteit - surface water - cyanobacteria - ultrasound - water quality - anabaena-flos-aquae - microcystis-aeruginosa - effective microorganisms - harmful cyanobacteria - growth-inhibition - climate-change - bloom control - gas vesicles - fresh-water - eutrophication
    The hypothesis that cyanobacteria can be controlled by commercially available ultrasound transducers was tested in laboratory experiments with cultures of the cyanobacteria Anabaena sp., Cylindrospermopsis raciborskii and Microcystis aeruginosa and the green alga Scenedesmus obliquus that were grown in the absence or presence of ultrasound (mix of 20, 28 and 44 kHz). The Scenedesmus experiment also included a treatment with the zooplankton grazer Daphnia magna. Chlorophyll-a and biovolume-based growth of Anabaena was significantly lower in ultrasound exposed cultures than in controls. Particle based growth rates were higher in ultrasound treatments. Filaments were significantly shorter in ultrasound exposed cultures reflecting filament breakage. Photosystem II efficiency was not affected by ultrasound. In Cylindrospermopsis chlorophyll-a based growth rates and photosystem II efficiencies were similar in controls and ultrasound treatments, but biovolume-based growth was significantly lower in ultrasound exposed cultures compared to controls. Despite biovolume growth rates of the filamentous cyanobacteria were reduced in ultrasound treatments compared to controls, growth remained positive implying still a population increase. In Microcystis and Scenedesmus growth rates were similar in controls and ultrasound treatments. Hence, no effect of ultrasound on these phytoplankton species was found. Ultrasound should not be viewed "environmental friendly" as it killed all Daphnia within 15 min, releasing Scenedesmus from grazing control in the cultures. Based on our experiments and critical literature review, we conclude that there is no music in controlling cyanobacteria in situ with the commercially available ultrasound transducers we have tested.
    Termination of a toxic Alexandrium bloom with hydrogen peroxide
    Burson, A. ; Matthijs, H.C.P. ; Bruijne, W. de; Talens, R. ; Hoogenboom, L.A.P. ; Gerssen, A. ; Visser, P.M. ; Stomp, M. ; Steur, K. ; Scheppingen, Y. van; Huisman, J. - \ 2014
    Harmful Algae 31 (2014). - ISSN 1568-9883 - p. 125 - 135.
    harmful algal blooms - northern baltic sea - ostenfeldii dinophyceae - water temperature - oxidative stress - shellfish toxins - eutrophication - cyanobacteria - phytoplankton - coastal
    The dinoflagellate Alexandrium ostenfeldii is a well-known harmful algal species that can potentially cause paralytic shellfish poisoning (PSP). Usually A. ostenfeldii occurs in low background concentrations only, but in August of 2012 an exceptionally dense bloom of more than 1 million cells L-1 occurred in the brackish Ouwerkerkse Kreek in The Netherlands. The A. ostenfeldii bloom produced both saxitoxins and spirolides, and is held responsible for the death of a dog with a high saxitoxin stomach content. The Ouwerkerkse Kreek routinely discharges its water into the adjacent Oosterschelde estuary, and an immediate reduction of the bloom was required to avoid contamination of extensive shellfish grounds. Previously, treatment of infected waters with hydrogen peroxide (H2O2) successfully suppressed cyanobacterial blooms in lakes. Therefore, we adapted this treatment to eradicate the Alexandrium bloom using a three-step approach. First, we investigated the required H2O2 dosage in laboratory experiments with A. ostenfeldii. Second, we tested the method in a small, isolated canal adjacent to the Ouwerkerkse Kreek. Finally, we brought 50 mg L-1 of H2O2 into the entire creek system with a special device, called a water harrow, for optimal dispersal of the added H2O2. Concentrations of both vegetative cells and pellicle cysts declined by 99.8% within 48 h, and PSP toxin concentrations in the water were reduced below local regulatory levels of 15 µg L-1. Zooplankton were strongly affected by the H2O2 treatment, but impacts on macroinvertebrates and fish were minimal. A key advantage of this method is that the added H2O2 decays to water and oxygen within a few days, which enables rapid recovery of the system after the treatment. This is the first successful field application of H2O2 to suppress a marine harmful algal bloom, although Alexandrium spp. reoccurred at lower concentrations in the following year. The results show that H2O2 treatment provides an effective emergency management option to mitigate toxic Alexandrium blooms, especially when immediate action is required.
    On the polyphasic quenching kinetics of chlorophyll a fluorescence in algae after light pulses of variable length
    Vredenberg, W.J. ; Prasil, O. - \ 2013
    Photosynthesis Research 117 (2013)1-3. - ISSN 0166-8595 - p. 321 - 337.
    photosystem-ii complexes - turnover excitations - induction kinetics - in-vivo - plants - chloroplasts - energy - yield - photosynthesis - cyanobacteria
    This study reports on kinetics of the fluorescence decay in a suspension of the alga Scenedesmus quadricauda after actinic illumination. These are monitored as the variable fluorescence signal in the dark following light pulses of variable intensity and duration. The decay reflects the restoration of chlorophyll fluorescence quenching of the photosystem II (PSII) antennas and shows a polyphasic pattern which suggests the involvement of different processes. The overall quenching curve after a fluorescence-saturating pulse (SP) of 250-ms duration, commonly used in pulse amplitude modulation applications as the tool for estimating the maximal fluorescence (Fm), has been termed P–O, in which P and O have the same meaning as used in the OJIP induction curve in the light. Deconvolution of this signal shows at least three distinguishable exponential phases with reciprocal rate constants of the order of 10, 102, and 103 ms. The size of the long ([103 ms) and moderate (*102 ms) lasting components relative to the complete quenching signal after an SP increases with the duration of the actinic pulse concomitantly with an increase in the reciprocal rate constants of the fast (*10 ms) and moderate quenching phases. Fluorescence responses upon single turnover flashes of 30-ls duration (STFs) given at discrete times during the P– O quenching were used as tools for identifying the quencher involved in the P–O quenching phase preceding the STF excitation. Results are difficult to interpret in terms of a single-hit two-state trapping mechanism with distinguishable quenching properties of open and closed reaction centers only. They give support for an earlier hypothesis on a double-hit three-state trapping mechanism in which the so-called semi-closed reaction centers of PSII are considered. In these trapping-competent centers the single reduced acceptor pair [PheQA]1-, depending on the size of photoelectrochemically induced pH effects on the QBbinding site, functions as an efficient fluorescence quencher.
    Evaluation of a Commercial Enzyme Linked Immunosorbent Assay (ELISA) for the Determination of the Neurotoxin BMAA in Surface Waters
    Faassen, E.J. ; Beekman-Lukassen, W.D. ; Lurling, M. - \ 2013
    PLoS ONE 8 (2013)6. - ISSN 1932-6203 - 7 p.
    methylamino-l-alanine - amino-acid - mass-spectrometry - cyanobacteria - chromatography - seeds - guam
    The neurotoxin ß-N-methylamino-L-alanine (BMAA) is suspected to play a role in Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis. Because BMAA seems to be produced by cyanobacteria, surface waters are screened for BMAA. However, reliable analysis of BMAA requires specialized and expensive equipment. In 2012, a commercial enzyme-linked immunosorbent assay (ELISA) for determination of BMAA in surface waters was released. This kit could enable fast and relatively cheap screening of surface waters for BMAA. The objective of this study was to determine whether the BMAA ELISA kit was suitable for the determination of BMAA concentrations in surface waters. We hypothesised that the recovery of spiked samples was close to 100% and that the results of unspiked sample analysis were comparable between ELISA and liquid chromatography tandem mass spectrometry (LC-MS/MS) analysis. However, we found that recovery was higher than 100% in most spiked samples, highest determined recovery was over 400%. Furthermore, the ELISA gave a positive signal for nearly each tested sample while no BMAA could be detected by LC-MS/MS. We therefore conclude that in its current state, the kit is not suitable for screening surface waters for BMAA.
    Brandstof kweken biedt zicht op schone toekomst
    Klein Lankhorst, R.M. - \ 2013
    Milieu : opinieblad van de Vereniging van Milieuprofessionals 2013 (2013)sept. - ISSN 1873-5436 - p. 11 - 13.
    zonne-energie - biobrandstoffen - biobased economy - duurzame energie - fotosynthese - stralingsbenuttigingsefficiëntie - cyanobacteriën - solar energy - biofuels - biobased economy - sustainable energy - photosynthesis - radiation use efficiency - cyanobacteria
    De zon is onze perfecte duurzame energiebron die we kunnen aftappen via fotosynthese. Planten doen dit al van nature, maar lang niet efficiënt genoeg. Daarom werkt het bedrijf BioSolar Cells aan de ontwikkeling van Solar Fuels: brandstoffen die rechtstreeks, zonder eerst biomassa te maken, worden gemaakt uit zonlicht, water en CO2. Dit kan met hoge efficiëntie en ondervangt bovendien een aantal knellende problemen met het gebruik van biomassa.
    Controlling eutrophication by combined bloom precipitation and sediment phosphorus inactivation
    Lürling, M.F.L.L.W. ; Oosterhout, J.F.X. - \ 2013
    Water Research 47 (2013)17. - ISSN 0043-1354 - p. 6527 - 6537.
    meren - oppervlaktewaterkwaliteit - eutrofiëring - cyanobacteriën - sedimentatie - uitvlokking - lanthaan - bentoniet - tests - fosfor - ecologisch herstel - noord-brabant - lakes - surface water quality - eutrophication - cyanobacteria - sedimentation - flocculation - lanthanum - bentonite - tests - phosphorus - ecological restoration - noord-brabant - prymnesium-parvum haptophyceae - harmful cyanobacterial blooms - dissolved organic-matter - rare-earth-elements - of-the-art - microcystis-aeruginosa - lake restoration - local soils - polyaluminum chloride - phosphate adsorption
    The hypothesis that the combination of the flocculent polyaluminium chloride (PAC) with the lanthanum-modified bentonite Phoslock® (Flock & Lock) could sink effectively a water bloom of cyanobacteria and could shift a turbid, cyanobacteria infested lake to a clear water lake was tested in a controlled laboratory experiment and a whole lake experiment. In the laboratory, a relatively low dose of the flocculent PAC (2.2 and 4.4 mg Al l-1) was insufficient to sediment positively buoyant cyanobacteria (Microcystis aeruginosa). Similarly, the lanthanum modified clay (dosed at 390 mg l-1) was insufficient to sediment the positively buoyant cyanobacteria. However, the combination of PAC and Phoslock® effectively sedimented cyanobacteria flocks. Likewise, a combined treatment of 2 tons PAC and 18 tons Phoslock® in Lake Rauwbraken in April 2008 effectively sedimented a developing cyanobacteria bloom of Aphanizomenon flos-aquae. The average chlorophyll-a concentration in the two years prior to this Flock & Lock treatment was 19.5 (±36.5) µg l-1, while it was as low as 3.7 (±4.5) µg l-1 in the years following the treatment. The combined treatment effectively reduced the amount of total phosphorus (TP) in the water column from on average 169 (±126) µg P l-1 before the application to 14 (±15) µg P l-1 after the treatment. Based on mean summer chlorophyll-a and TP concentrations, the lake was shifted from a eutrophic/hypertrophic state to an oligo/mesotrophic state. From directly after treatment in April 2008 until and including 2013, Lake Rauwbraken remained in an oligo-mesotrophic clear water state with TP reduced to less than 10% of the pre-treatment. This result shows that eutrophication in relatively small, isolated, stratifying lakes can be restored by targeting both water column and sediment P using a combination of flocculent and solid phase P-sorbent
    Light harvesting and photoprotection in Cyanobacteria
    Tian, L. - \ 2013
    Wageningen University. Promotor(en): Herbert van Amerongen. - [S.l.] : s.n. - ISBN 9789461735294 - 167
    cyanobacteriën - fotosynthese - light harvesting complexen - fluorescentie - lichtverdeling - cyanobacteria - photosynthesis - light harvesting complexes - fluorescence - light distribution

    The process of photosynthesis has been studied for centuries, but despite a large amount of progress, there are still many aspects that are not fully understood. An important part of the progress is the fact that many structures of photosynthetic complexes have been resolved 1,2and these complexes have been studied separately in great detail, amongst other with ultrafast spectroscopic techniques. These studies allow to monitor excitation-energy transfer (EET) and charge separation (CS), the first crucial processes after the absorption of a photon. Many picosecond studies have also been performed in vivo in the past before the crystal structures were known, but due to an additional lack of knowledge about the organization and composition of the thylakoid membrane where most of the EET and CS processes take place, the obtained results were difficult to interpret. More recently, new interest has arisen in in vivo studies on photosynthetic organisms because a lot of molecular and organizational information has been obtained but also because the spectroscopic techniques have improved and mutants have become available that allow to study the effect of specific modifications in the organisms. This thesis focuses on the study of the light energy harvesting processes of photosynthetic complexes in cyanobacteria in general by using time-resolved fluorescence techniques, and with particular emphasis on the study of the in vivo protective process of non-photochemical quenching (NPQ) that is induced in the presence of high intensities of blue-green light.

    Photosynthetic efficiency and oxygen evolution of Chlamydomonas reinhardtii under continuous and flashing light
    Vejrazka, C. ; Janssen, M. ; Benvenuti, G. ; Streefland, M. ; Wijffels, R.H. - \ 2013
    Applied Microbiology and Biotechnology 97 (2013)4. - ISSN 0175-7598 - p. 1523 - 1532.
    photobioreactors - phytoplankton - cyanobacteria - irradiance - microalgae - growth
    As a result of mixing and light attenuation in a photobioreactor (PBR), microalgae experience light/dark (L/D) cycles that can enhance PBR efficiency. One parameter which characterizes L/D cycles is the duty cycle; it determines the time fraction algae spend in the light. The objective of this study was to determine the influence of different duty cycles on oxygen yield on absorbed light energy and photosynthetic oxygen evolution. Net oxygen evolution of Chlamydomonas reinhardtii was measured for four duty cycles (0.05, 0.1, 0.2, and 0.5) in a biological oxygen monitor (BOM). Oversaturating light flashes were applied in a square-wave fashion with four flash frequencies (5, 10, 50, and 100 Hz). Algae were precultivated in a turbidostat and acclimated to a low photon flux density (PFD). A photosynthesis-irradiance (PI) curve was measured under continuous illumination and used to calculate the net oxygen yield, which was maximal between a PFD of 100 and 200 µmol m(-2)¿s(-1). Net oxygen yield under flashing light was duty cycle-dependent: the highest yield was observed at a duty cycle of 0.1 (i.e., time-averaged PFD of 115 µmol m(-2)¿s(-1)). At lower duty cycles, maintenance respiration reduced net oxygen yield. At higher duty cycles, photon absorption rate exceeded the maximal photon utilization rate, and, as a result, surplus light energy was dissipated which led to a reduction in net oxygen yield. This behavior was identical with the observation under continuous light. Based on these data, the optimal balance between oxygen yield and production rate can be determined to maximize PBR productivity.
    First report of (homo)anatoxin-a and dog neurotoxicosis after ingestion of benthic cyanobacteria in The Netherlands
    Faassen, E.J. ; Harkema, H. ; Begemann, L.L.J. ; Lürling, M.F.L.L.W. - \ 2012
    Toxicon 60 (2012)3. - ISSN 0041-0101 - p. 378 - 384.
    zwemwater - cyanobacteriën - toxinen - waterverontreiniging - oppervlaktewater - ijsselmeer - nederland - swimming water - cyanobacteria - toxins - water pollution - surface water - lake ijssel - netherlands - blue-green-algae - fresh-water - anatoxin-a - mass-spectrometry - homoanatoxin-a - identification - cylindrospermopsin - biosynthesis - microcystin
    In April and May 2011, three dogs died and one dog became ill after swimming in Lake IJmeer (The Netherlands). At the time, the lake was infested with the benthic cyanobacterial species Phormidium. A Eurasian Coot (Fulica atra) and a Black-headed Gull (Chroicocephalus ridibundus) also died near Lake IJmeer in the same period. One of the dogs and both birds were subjected to a pathological investigation. Furthermore, the Phormidium mat; algal samples from the dikes; contents of the animals' digestive systems and organ tissues were analysed for the following cyanobacterial toxins: (homo)anatoxin-a; (7-deoxy-)cylindrospermopsin; saxitoxins and gonyautoxins by LC-MS/MS. Samples were also analysed for the nontoxic (homo)anatoxin-a metabolites dihydro(homo)anatoxin-a and epoxy( homo) anatoxin-a. The dog necropsy results indicated neurotoxicosis and its stomach contained Phormidium filaments. Anatoxin-a was detected in the Phormidium mat (272 mu g g(-1) dry weight, stdev 65, n = 3) and in the dog's stomach contents (9.5 mu g g(-1) dry weight, stdev 2.4, n = 3). Both samples also contained the anatoxin-a metabolite dihydroanatoxin-a, and a trace of homoanatoxin-a was detected in the Phormidium mat. The birds were in bad nutritive condition at the time of necropsy and their stomachs and intestines did not contain any cyanobacterial material. Furthermore, no cyanobacterial toxins were detected in their stomachs, intestines and organs and they both had lesions that are not associated with cyanobacterial intoxication. This is the first report of anatoxin-a and homoanatoxina occurrence in The Netherlands, these toxins have likely caused the deaths of three dogs. The birds probably died of other causes. Dutch recreational waters are at this moment only screened for pelagic cyanobacterial species, the current bathing water protocol therefore does not protect humans and animals from negative effects of blooms of benthic cyanobacteria.
    Bestrijding blauwalgenoverlast : eindrapportage praktijkonderzoek
    Lürling, M.F.L.L.W. ; Engels, B. ; Waajen, G. ; Zanten, H. van; Turlings, L. - \ 2012
    Amersfoort : Stowa (Rapport / STOWA 2012-42) - ISBN 9789057735752 - 169
    oppervlaktewaterkwaliteit - eutrofiëring - cyanobacteriën - fosfaat - aquatische ecologie - zwemwater - plassen - visbestand - stedelijke gebieden - noord-brabant - biologische behandeling - surface water quality - eutrophication - cyanobacteria - phosphate - aquatic ecology - swimming water - ponds - fishery resources - urban areas - noord-brabant - biological treatment
    Wat zijn de aanpak en maatregelen of combinaties van maatregelen, die bijdragen aan het structureel bestrijden van overlast door blauwalgen? Dat is binnen het onderzoeksproject Kansrijke Innovatieve Maatregelen Bestrijding Blauwalgenoverlast onderzocht. Dit project heeft als belangrijkste doel om meer inzicht te krijgen in de kosteneffectiviteit van veelbelovende maatregelen om interne nalevering te beteugelen. Hiertoe zijn een aantal structurele, kansrijke maatregelen voor verbetering van de oppervlaktewaterkwaliteit in plassen en stedelijk water op praktijkschaal getest, zoals in zwemplas De Kuil (Prinsenbeek) met regelmatig blauwalgenoverlast, en in twee vijvers te Dongen en Eindhoven waarin verschillende compartimenten zijn aangelegd. Hierin zijn actief biologisch beheer (visstandbeheer, waterplanten uitzetten), baggeren (al dan niet met een vlokmiddel) en chemisch P-fixatie met lanthaan gemodificeerde klei (met en zonder vlokmiddel) onderzocht.
    Controlling toxic cyanobacteria: effects of dredging and phosphorus-binding clay on cyanobacteria and microcystins
    Lürling, M.F.L.L.W. ; Faassen, E.J. - \ 2012
    Water Research 46 (2012)5. - ISSN 0043-1354 - p. 1447 - 1459.
    oppervlaktewaterkwaliteit - meren - herstelbeheer - eutrofiëring - cyanobacteriën - lanthaan - klei - vergelijkend onderzoek - aquatische ecologie - surface water quality - lakes - restoration management - eutrophication - cyanobacteria - lanthanum - clay - comparative research - aquatic ecology - rare-earth-elements - lake restoration - organic-matter - shallow lakes - sediment removal - northern poland - urban lake - blooms - water - fresh
    Sediment dredging and Phoslock(®) addition were applied individually and in combination in an enclosure experiment in a Dutch hypertrophic urban pond. These measures were applied to control eutrophication and reduce the risk of exposure to cyanobacterial toxins. Over the 58 days course of the experiment, cyanobacteria (predominantly Microcystis aeruginosa) gradually decreased until they dropped below the level of detection in the combined treated enclosures, they were reduced in dredged enclosures, but remained flourishing in controls and Phoslock(®) treated enclosures. Cyanobacteria were, however, less abundant in the enclosures (medians chlorophyll-a 30-87 µg l(-1)) than in the pond (median chlorophyll-a 162 µg l(-1)), where also a thick surface scum covered one-third of the pond for many weeks. Soluble reactive phosphorus (SRP), total phosphorus and total nitrogen concentrations were significantly lower in the combined dredged and Phoslock(®) treated enclosures than in controls. Median SRP concentrations were 24 µg P l(-1) in the combined treatment, 58 µg P l(-1) in dredged enclosures, and 90 µg P l(-1) in controls and 95 µg P l(-1) in Phoslock(®) treated enclosures. Hence, the combined treatment was most effective in decreasing SRP and TP, and in lowering cyanobacterial biomass. Microcystin (MC) concentrations were analyzed by LC-MS/MS. MC concentrations and cyanobacterial biomass were positively correlated in all treatments. Mean MC concentrations in controls (71 µg l(-1)), Phoslock(®) treated enclosures (37 µg l(-1)) and dredged enclosures (25 µg l(-1)) exceeded the provisional guideline of 20 µg l(-1), whereas mean MC concentrations were 13 µg l(-1) in the combined treated enclosures. All samples contained the MC variants dmMC-RR, MC-RR, MC-YR, dmMC-LR and MC-LR; traces of MC-LY and nodularin were detected in few samples. The different treatments did not change the relative contribution of the variants to the MC pool; MC profiles in all treatments and the pond showed dominance of MC-RR followed by MC-LR. In the surface scum of the pond, total MC concentration was extremely high (64000 µg l(-1) or 1300 µg g(-1) DW), which poses a serious health hazard to children playing on the banks of the pond. Based on our results and pond characteristics, we propose combined sediment dredging and Phoslock(®) addition, fish removal and strong reduction of duck feeding by the neighborhood as most promising measures controlling cyanobacterial hazards in this pond.
    Photosynthetic efficiency of Chlamydomonas reinhardtii in attenuated, flashing light
    Vejrazka, C. ; Janssen, M.G.J. ; Streefland, M. ; Wijffels, R.H. - \ 2012
    Biotechnology and Bioengineering 109 (2012)10. - ISSN 0006-3592 - p. 2567 - 2574.
    quantum yield - photobioreactors - cyanobacteria - dependence - microalgae
    As a result of mixing and light attenuation, algae in a photobioreactor (PBR) alternate between light and dark zones and, therefore, experience variations in photon flux density (PFD). These variations in PFD are called light/dark (L/D) cycles. The objective of this study was to determine how these L/D cycles affect biomass yield on light energy in microalgae cultivation. For our work, we used controlled, short light path, laboratory, turbidostat-operated PBRs equipped with a LED light source for square-wave L/D cycles with frequencies from 1 to 100¿Hz. Biomass density was adjusted that the PFD leaving the PBR was equal to the compensation point of photosynthesis. Algae were acclimated to a sub-saturating incident PFD of 220¿µmol¿m(-2) ¿s(-1) for continuous light. Using a duty cycle of 0.5, we observed that L/D cycles of 1 and 10¿Hz resulted on average in a 10% lower biomass yield, but L/D cycles of 100¿Hz resulted on average in a 35% higher biomass yield than the yield obtained in continuous light. Our results show that interaction of L/D cycle frequency, culture density and incident PFD play a role in overall PBR productivity. Hence, appropriate L/D cycle setting by mixing strategy appears as a possible way to reduce the effect that dark zone exposure impinges on biomass yield in microalgae cultivation. The results may find application in optimization of outdoor PBR design to maximize biomass yields.
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