1,721,047 research outputs found
Host genotype influences the assembly of both the gut microbiota and the surrounding bacterioplankton
No full textPresentation at IGC (Microbiome Eo-evo symposium)status: Publishe
Biological control of ciliate contamination in <i>Chlamydomonas</i> culture using the predatory copepod <i>Acanthocyclops robustus </i>
No full text© 2018 Elsevier B.V. Ciliates are a common but less-explored group of contaminants in microalgal cultures that feed on microalgae and can cause severe losses in productivity of cultures. The aim of this study was to evaluate the potential of biological control to eradicate ciliates from microalgal cultures. In lab-scale experiments, we used the carnivorous cyclopoid copepod Acanthocyclops robustus as a biological control agent to eliminate the ciliate Sterkiella from cultures of the microalga Chlamydomonas. Our experiments showed that the copepod Acanthocyclops robustus can consume up to 400 ciliates individual−1 day−1. Addition of 0.07 copepods mL−1 to a culture that was contaminated with 10 ciliates mL−1 resulted in a complete elimination of ciliates from the culture within 1 day and restored the algal biomass production at the level of a non-contaminated culture. Addition of copepods to a fresh Chlamydomonas culture did not cause a reduction in the microalgal biomass concentration, indicating that this copepod does not feed on Chlamydomonas. These laboratory-scale experiments indicate that copepods have potential to be used as a biological control agent to address the problem of contamination of large-scale microalgal cultures by ciliates.sponsorship: The authors are grateful to three anonymous reviewers for their constructive comments, which helped us improve the manuscript. The authors thank KU Leuven University for funding this research through grant OT/14/065. The first author would like to acknowledge the Ministry of Education and Training of Vietnam for funding the PhD program. D. Vandamme is a researcher funded by the Research Foundation - Flanders Belgium (FWO) (2016-2019 12D8917N). (KU Leuven University|OT/14/065, Ministry of Education and Training of Vietnam, Research Foundation - Flanders Belgium (FWO)|2016-2019 12D8917N)status: Publishe
Omgevingsafhankelijkheid van gastheer-microbiota interacties bij Daphnia magna ,,
No full textstatus: Publishe
Context afhankelijkheid van gastheer-parasiet interacties: Invloed van Microcystis aeruginosa op parasitisme in Daphnia magna
No full textIn the last decade, it has become clear that changing environmental conditions may affect host-parasite interactions. Nevertheless, it is often not clear in what way they affect these interactions. In freshwater ecosystems, changing circumstances, such as nutrient enrichment, can induce toxic cyanobacterial blooms. We here investigate whether the widespread and frequently studiednbsp;species Microcystis aeruginosa has an effect on an infectious disease in Daphnia magna, a filter-feeding zooplankton species living in freshwater. The parasite that we study causes White Bacterial Disease (WBD), a virulent infectious disease in Daphnia that induces peculiar phenotypic effects in the adipose tissue.
In the first part of the thesis, we evaluated the impact of direct and indirect effects of different M. aeruginosa strains onD. magna exposed to WBD. Microcystins are one of the most common toxins produced by cyanobacteria. However, not all cyanobacterial negative effects are attributed to these toxins. Cyanobacteria can also produce other less harmful bio-active metabolites and they are low quality food for zooplankton due to the absence of polyunsaturated fatty acids and sterols. To evaluate these non-toxic impacts, a non-microcystin-producing M. aeruginosa strain was tested. Results demonstratednbsp;M. aeruginosa protected D. magna against parasitism. Increasing M. aeruginosanbsp;reduced the percentage of infected individuals and antagonistic effects between M. aeruginosa and thenbsp;were found on different life-history characteristics of D. magna. Plating experiments showed a directnbsp;effect of M. aeruginosa on bacterial growth, which may explain the direct, antagonistic effect. In the next chapter, we investigated the effect of a microcystin-producing M. aeruginosa strain and its microcystin-lacking mutant on the susceptibility of D. magna to WBD. As direct effects of these strains against bacteria were absent, focus wasnbsp;to indirect effects. We focused on differences in clearance rate. Clearance rates cannbsp;disease as most Daphnia parasites are taken up by grazing. We comparednbsp;populations, each originating from a different pond. The results demonstrated that the population with a higher clearance rate in the presence of the microcystin producing M. aeruginosa strain, was more susceptible to disease than the population with a lower clearance rate, as they were earlier infected and produced less offspring upon simultaneous exposure to the parasite and the microcystin producing M. aeruginosa strain. These results show that the presence of cyanobacteria can indirectlynbsp;an organism more susceptible to disease due to thenbsp;of trait changes in this organism.
Then, attempts were made to characterize WBD in Daphnia. Literature indicates that WBD may be caused by a coccoid bacterium. Thus, the bacterial community of WBD infected and control D. magna was analyzed by Denaturing Gradient Gel Electrophoresis and compared. Thenbsp;suggested the involvement of the genera Flavobacterium and Emticicia, both members of the Bacteroidetes. Asnbsp;is characterized by changes in the adipose tissue, the degree of lipid oxidation in WBD infected and control D. magna wasnbsp;Results showed that WBD infected D. magna contained morenbsp;fatty acids than control D. magna. Moreover, Bacteroidetes were found in the adipose tissue of WBD infected D. magna. Nevertheless, so far we cannot exclude that Flavobacterium and/orEmticicia are only opportunists associated with WBD andnbsp;other agents induce the disease. Therefore, alternative analyses (e.g. 16S RNA gene pyrosequencing of infected and control individuals) are suggested.
Innbsp;last chapter, the establishment of an additional host-parasite study system Microcystis and its cyanophages (viruses of cyanobacteria) is described. We aimed to develop a Microcystis-cyanophage model system to study environmental influences on host-parasite interactions. We succeeded to isolate Microcystis strains and cyanophage strains from 22 ponds in Belgiumnbsp;started to optimize the model system. The Microcystis strains werenbsp;and identified via the 16S-23S rDNAnbsp;transcribed spacer (ITS). These data showed geographical diversity, as there was a difference between West-Middle Belgian strains and East Belgian strains, but many Microcystis strains from the same pond/region, shared the same ITS sequence. We attempted to distinguishnbsp;strains further by a higher resolution DNA fingerprinting technique (HIP1), but as not all cultures were axenic, we could not relynbsp;this technique.nbsp;also succeeded tonbsp;cyanophagesnbsp;double layer plaques assay andnbsp;quantify them via epifluorescence microscopy, but we were not able to characterize them molecularly.
In conclusionnbsp;can state that cyanobacteria influence disease in Daphnia either in a positive or a negative way depending on the cyanobacterial strainnbsp;and the fact if they cause direct or indirect effects on the D. magna-WBD interaction. Further, our results suggest that the genera Flavobacterium and Emticicia may be involved innbsp;disease of WBD, but further researchnbsp;needed to confirm if thesenbsp;are the causative agents. Finally, we can state that Microcystisnbsp;cyanophages, but we could not develop a successful technique to perform experiments to study environmental effects on Microcystis-cyanophage interactions or on multi-trophic interactions between cyanophages-Microcystis-Daphnia-parasites.status: Publishe
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Detectie en controle van rotifeer contaminatie in microalgen culturen
No full textMicroalgae are a promising new source of biomass for production of food, feed, fuel or bulk chemicals. Today, microalgae production is moving from lab-scale to full-scale production. One of the major challenges in large-scale systems are grazing predators (e.g. protozoa, rotifers, microcrustaceans), which can infest cultures and decimate microalgal biomass within days. So far, there has barely been research into the identity of these predators, their impact on productivity and how to effectively control them. There is a need for innovative approaches for crop control of microalgae, preferably using ecological methods that avoid the unsustainable use of chemical pesticides.
The aim of this PhD study is to control microalgal predators based on ecological principles. The focus will be on ciliate predators, which are poorly known and are difficult to control. In the first phase of the PhD project, potential contamination routes will be investigated. Next, microalgal predators will be isolated and their impact on multiple freshwater and marine microalgal cultures will be assessed. Methods (i.e. flow cytometry) and predictive models will be developed to monitor and forecast predators' impact in these cultures. The project will attempt to control ciliates by a trophic cascade, i.e. by introducing predators that feed on ciliates. Besides this top-down control also a bottom-up control that relies on the principle of ecological stoichiometry will be considered. Ultimately, we will also attempt to control ciliates by means of feeding deterrents that are naturally produced by specific microalgae.status: Publishe
Voedings-afhankelijke dynamieken van infectieziekten
No full textNormal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 It is commonlyassumed that infectious disease dynamics in host populations depend on thenutritional status of the host. However, the extent to which and the mechanismsvia which nutrition contributes to infectious disease dynamics in animalpopulations remains unclear. In this study of nutrition dependence oninfectious diseases we focused on symbionts of Daphnia magna, an aquatic invertebrate host that has beencharacterized by the presence of a multitude of symbiotic (epibiont andparasitic) taxa. It is straightforward to manipulate host nutrition in Daphnia, given that Daphnia can be fed different quantities of algae or algal taxa thatdiffer in food quality (mainly presence of LC-PUFAs and sterols). We observedthat the symbiont community of Daphniashifts towards more parasitism along an increasing food quantity gradient,likely due to a positive correlation between food quantity and host density. Ingeneral, we did not observe an individual based host immunity enhanced effect ofthe tested higher quality food upon parasite exposure. Nevertheless, ourexperiments provided support for the nutrition quality dependence on infectiousdisease dynamics in populations and in multiple infections, based on changes inthe host demography and parasite interspecific interactions. By using amultifactorial experimental approach, we were able to detect interactionsbetween parasitism and nutritional quality. We showed that food qualityinfluences the competition between parasite species in multiple-infected hostpopulations. In a further step, we predicted virulence levels in multipleinfections based on host population and parasite parameters that were obtainedvia experiments and that were integrated in a theoretical model. This modelshowed that the detected food quality effect on host demography and parasiteinteractions were mechanistically translated into different virulence levels. Wecan conclude that a theoretical approach to predict virulence in multipleinfected host populations is useful to understand virulence levels of hostmodel systems in which infection trials and field studies are complex or are economicallyor ethically challenging. Based on our findings of standardized laboratoryexperiments, we next assumed a strong nutrition dependence on realistic infectiousdisease dynamics in the Daphnia-parasitemodel system. Therefore, we manipulated food quality in mesocosm experimentsand concluded that food quality induced changes in semi-natural diseasedynamics are complex, given that they interact with other biological factors,such as predation. We observed that food quality affects the prevalence of theparasite causing White Bacterial Disease in Daphniapopulations and that food quality can interact with predation affectingdensities of parasitized host populations. In a last and additional study, weinvestigated the life history of the gut parasite Pansporella perplexa, which is an amoebic organism living inassociation with the microbiota of the D.magna gut. Based on the fact that P.perplexa has taxonomically closely related counterparts which are humanparasites, it delivers a unique possibility to study nutrition dependence ofinfection intensity and prevalence of amoebae in real-time and to obtaininsight in nutritionally influenced diarrhetic diseases. In conclusion, we canstate that the added value of this study is that it connected mathematicalmodels with experimental studies under laboratory and semi-natural conditions,which proved to be helpful to gain more insight into the effects and themechanisms of nutrition on infectious disease dynamics in invertebrates.Investigating D. magna and itsparasites as a model system provided us with answers to ecological andepidemiological questions, which furthers our understanding of interactionsbetween host nutrition and infectious diseases in general. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;}status: Publishe
Het effect van een veranderende N:P ratio op Daphnia-parasiet interacties
No full textEutrophication and parasitism are both persistent stressors shaping populations, communities and ecosystems. Spatiotemporal variation in environmental factors can strongly drive the expression of host-parasite parameters. To gain a better insight into how environmental changes impact host-parasite interactions and the eco-evolutionary consequences, it is essential to gain a deeper insight into epidemiological and evolutionary processes that drive host-parasite interactions at different spatial, temporal and ecological scales. In this thesis, the impact of changing food quality in terms of a changing phytoplankton N:P ratio on host-parasite interactions was investigated in the zooplankton key stone grazer Daphnia. We approached the food quality - host - parasite “disease triangle” from different perspectives, from the individual over the population to the community level and within a framework of temporal and spatial variation. This multi-level approach in a well-known experimental pathosystem delivered insight to be able to predict and understand the emergence, spread and the evolution of infectious diseases.status: Publishe
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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