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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Engineering the unicellular alga Phaeodactylum tricornutum for high-value plant triterpenoid production
Adamo, Sarah D'; Schiano di Visconte, Gino ; Lowe, Gavin ; Szaub-Newton, Joanna ; Beacham, Tracey ; Landels, Andrew ; Allen, Michael J. ; Spicer, Andrew ; Matthijs, Michiel - \ 2018
Plant Biotechnology Journal 17 (2018)1. - ISSN 1467-7644 - p. 75 - 87.
algal synthetic biology - betulin - blue biotechnology - diatoms - lupeol - microalgae - natural product - triterpenoid biosynthesis

Plant triterpenoids constitute a diverse class of organic compounds that play a major role in development, plant defence and environmental interaction. Several triterpenes have demonstrated potential as pharmaceuticals. One example is betulin, which has shown promise as a pharmaceutical precursor for the treatment of certain cancers and HIV. Major challenges for triterpenoid commercialization include their low production levels and their cost-effective purification from the complex mixtures present in their natural hosts. Therefore, attempts to produce these compounds in industrially relevant microbial systems such as bacteria and yeasts have attracted great interest. Here, we report the production of the triterpenes betulin and its precursor lupeol in the photosynthetic diatom Phaeodactylum tricornutum, a unicellular eukaryotic alga. This was achieved by introducing three plant enzymes in the microalga: a Lotus japonicus oxidosqualene cyclase and a Medicago truncatula cytochrome P450 along with its native reductase. The introduction of the L. japonicus oxidosqualene cyclase perturbed the mRNA expression levels of the native mevalonate and sterol biosynthesis pathway. The best performing strains were selected and grown in a 550-L pilot-scale photobioreactor facility. To our knowledge, this is the most extensive pathway engineering undertaken in a diatom and the first time that a sapogenin has been artificially produced in a microalga, demonstrating the feasibility of the photo-bio-production of more complex high-value, metabolites in microalgae.

Mechanism behind autoflocculation of unicellular green microalgae
Salim, S. ; Kosterink, N. ; Tchetkoua Wacka, N.D. ; Vermue, M.H. ; Wijffels, R.H. - \ 2014
Journal of Biotechnology 174 (2014). - ISSN 0168-1656 - p. 34 - 38.
algogenic organic-matter - flocculation - diatoms
The oleaginous Ettlia texensis is an autoflocculating green microalga that can be used for bio-flocculation of other microalgae species to facilitate harvesting. In this study the mechanism behind autoflocculation of E. texensis was revealed by scanning electron microscopy (SEM) analysis and by characterisation of the cell surface properties. SEM analysis and measurement of extracellular polymeric substances (EPS) showed that autoflocculation of E. texensis is due to the EPS containing mainly glycoproteins patched to the cell surface. Despite the presence of charged groups on the cell surface, they do not seem to attribute to autoflocculation of E. texensis. During bio-flocculation of E. texensis with Chlorella vulgaris EPS structures between both microalgal species were observed. EPS thus not only play a predominant role in autoflocculation of E. texensis but also in bio-flocculation when using this microalga to harvest others.
Alternative states and population crashes in a resource-susceptible-infected model for planktonic parasites and hosts
Gerla, D.J. ; Gsell, A.S. ; Kooi, B.W. ; Ibelings, B.W. ; Donk, E. van; Mooij, W.M. - \ 2013
Freshwater Biology 58 (2013)3. - ISSN 0046-5070 - p. 538 - 551.
fresh-water phytoplankton - aquatic food webs - asterionella-formosa - viral-infection - dynamics - growth - diseases - diatoms - blooms - fungi
1. Despite the strong impact parasites can have, only few models of phytoplankton ecology or aquatic food webs have specifically included parasitism. 2. Here, we provide a susceptible-infected model for a diatom-chytrid hostparasite system that explicitly includes nutrients, infected and uninfected hosts, reproduction of the parasite on the hosts and free-living infective stages. 3. A distinguishing feature of the model is that parasite reproduction on host increases with nutrient availability to the infected host, as has been observed for many parasites and viruses. 4. It follows from this assumption that the parasite's basic reproduction number, R0, increases with nutrient concentration, because at higher nutrient concentrations, infected hosts consume more nutrients that are used for the reproduction of the parasite. 5. Another important result is that there may be two alternative states to which population densities can converge: one with only the host and one with host and parasite co-existing. In the latter, the parasite can invade a host population only if it is introduced above a threshold density. 6. Furthermore, the model shows a strong tendency for hostparasite cycles, which may be chaotic. Nutrient enrichment leads to increasing amplitude of these cycles, which may cause host or parasite population extinction caused by stochastic fluctuations during periods of low population density, which is the Paradox of Enrichment. 7. Finally, if alternative states and cycles co-occur, increased population cycle amplitude may drive the parasite below its threshold density for successful invasion, causing parasite extinction in a deterministic Paradox of Enrichment'. Published results confirm that hostparasite cycles and collapse of hostparasite systems may occur in real plankton communities. 8. Our results underline that ecological detail in hostparasite models may have consequences for disease dynamics that may be overlooked when ecological interactions between environment, host and parasite are not explicitly taken into account.
Increase of atmospheric CO2 promotes phytoplankton productivity
Schippers, P. ; Lürling, M.F.L.L.W. ; Scheffer, M. - \ 2004
Ecology Letters 7 (2004)6. - ISSN 1461-023X - p. 446 - 451.
inorganic carbon acquisition - marine-phytoplankton - emiliania-huxleyi - dioxide - growth - lakes - availability - diatoms - impact - system
It is usually thought that unlike terrestrial plants, phytoplankton will not show a significant response to an increase of atmospheric CO2. Here we suggest that this view may be biased by a neglect of the effects of carbon (C) assimilation on the pH and the dissociation of the C species. We show that under eutrophic conditions, productivity may double as a result of doubling of the atmospheric CO2 concentration. Although in practice productivity increase will usually be less, we still predict a productivity increase of up to 40% in marine species with a low affinity for bicarbonate. In eutrophic freshwater systems doubling of atmospheric CO2 may result in an increase of the productivity of more than 50%. Freshwaters with low alkalinity appeared to be very sensitive to atmospheric CO2 elevation. Our results suggest that the aquatic C sink may increase more than expected, and that nuisance phytoplankton blooms may be aggravated at elevated atmospheric CO2 concentrations.
Co-correspondence analysis: a new ordination method to relate two community compositions
Braak, C.J.F. ter; Schaffers, A.P. - \ 2004
Ecology 85 (2004)3. - ISSN 0012-9658 - p. 834 - 846.
partial least-squares - canonical correspondence-analysis - regression - reconstruction - biplots - diatoms - pls - ph
A new ordination method, called co-correspondence analysis, is developed to relate two types of communities (e.g., a plant community and an animal community) sampled at a common set of sites in a direct way. The method improves the simple, indirect approach of applying correspondence analysis (reciprocal averaging) to the separate species data sets and correlating the resulting ordination axes. Co-correspondence analysis maximizes the weighted covariance between weighted averaged species scores of one community and weighted averaged species scores of the other community. It thus attempts to identify the patterns that are common to both communities. Both a symmetric descriptive and an asymmetric predictive form are developed. The symmetric form relates to co-inertia analysis and the asymmetric, predictive form to partial least-squares regression. In two examples the predictive power of co-correspondence analysis is compared with that of canonical correspondence analyses on syntaxonomic and environmental data. In the first example, carabid beetles in roadside verges are shown to be more closely related to plant species composition than to vegetation structure (biomass, height, roughness, among others), and, in the second example, bryophytes in spring meadows are shown to be more closely related to the species composition of the vascular plants than to the measured water chemistry.
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