381023 research outputs found
Sort by
Experimental exploration of the evolutionary potential of polyploid plants
No full textGenoomduplicatie is een algemene mutatie in planten die gepaard gaat met hoge kosten. Toch is een aanzienlijk deel van de gekende plantensoorten polyploid en wordt plantenevolutie gekenmerkt door cycli van polyploïdisaties en diploïdisaties. Dergelijke paleopolyploïdisaties zijn niet gelijkmatig verdeeld over de tijd, maar lijken ze te clusteren rond periodes van intense omgevingsveranderingen. Dit suggereert dat een oorsprong in een instabiele, veranderende omgeving een voorwaarde is voor polyploïd succes op de lange termijn. In deze thesis ontwikkelen en gebruiken we het eencellige groenwier Chlamydomonas reinhardtii, en het veelwortelig kroos Spirodela polyrhiza als modelsystemen om onderzoek te doen naar eigenschappen van polyploïde planten die een verklaring kunnen bieden voor hun evolutionair succes en de link met grote omgevingsveranderingen. We tonen aan dat (1) de abundantie van metabolieten per cel stijgt met het aantal genoomkopieën, maar dat dit effect op biomassaniveau deels wordt gecompenseerd door een verhoogde celgrootte, (2) de onmiddellijke effecten van genoom duplicatie polyploïden een voordeel kunnen opleveren in uitdagende omstandigheden, (3) genoom duplicatie een mutator mutatie is die drastische verandering in de snelheid en het spectrum van moleculaire evolutie teweeg kan brengen en (4) verschillende onafhankelijke polyploïdisaties verder kunnen helpen in de vestiging van een soort onder uitdagende omstandigheden
Muscle structure, weakness and strengthening : a complex traingle for children with spastic cerebral palsy
No full text
Towards a better understanding of the solitary bee and Asian hornet gut microbiota
No full textThe current Anthropocene epoch is characterized by major changes in the environment and biogeochemical systems at the global scale. Within this changing landscape, pollinators, including bees and wasps, are threatened by a variety of stressors, such as changes in land use, introduction of pathogens and alien species, use of pesticides, and climate change. While most species are negatively affected by the effects of the Anthropocene, some species seem to thrive well in the changing environmental conditions by expanding their geographical range. A better understanding of the effects of climate change on pollinators and their adaptability was the objective of the interuniversity ‘Climate change and effect on Pollination Services’ (CliPS) project. In order to fully understand the effect of climate change and the adaptability of pollinators, it is necessary to also study the gut microbiota. Therefore, different gut microbiota studies were performed during the present PhD, as part of the CliPS project, and aimed to characterize and identify the microbial communities associated with native solitary bees and invasive aculeate species.
Solitary bees account for the majority of approximately 20,000 known bee species. However, their gut microbial communities have been rarely studied compared to those of social bees. In a first study, we described the bacterial and fungal gut microbiota of the crop, midgut, hindgut, and ovaries of four solitary bee species commonly occurring in Belgium, i.e. Andrena vaga, Anthophora plumipes, Colletes cunicularius and Osmia cornuta, using a combination of amplicon sequencing and culturomics. The microbial communities were dominated by endosymbionts of the genera Wolbachia and Spiroplasma, and environmental bacteria and yeasts with high metabolic versatility. The bacterial communities varied between gut fractions and appeared to be species-specific. Additionally, we obtained a total of 1,510 isolates from the different fractions of each bee species during a large-scale isolation campaign. The obtained reference cultures were identified at the species-level and can be used for functional analyses in future studies.
In a second study, we characterized the gut microbiota of eight solitary bee species sampled in apple orchards along a latitudinal axis in Europe, thus representing a climate gradient. The aim of this study was to determine the factors involved in shaping the solitary bee bacterial and fungal communities. Host species and location were the main factors that influenced the microbiota composition of these bees, and infections with parasites led to changes in the microbial community. The bacterial community was more host specific and most strongly impacted by bee community and landscape variables, compared to the fungal community which was more strongly influenced by the local environment and climate variables. Parasite infection appeared to be host specific and resulted in a state of dysbiosis, which was characterized by increased richness and diversity and which changed the microbial community composition.
The two invasive aculeate species currently occurring in Europe, the solitary bee Megachile sculpturalis and the Asian hornet Vespa velutina, belong to the few species that are thriving during the current environmental changes. They were the subjects of two additional studies of the present PhD. Both species were accidentally introduced to Europe from Asia as a result of globalization and trading of goods. They have successfully expanded their range in Europe since their arrival. Yet, the mechanisms underlying the invasion success of these species are not fully understood. We wanted to evaluate to what extent the microbial communities may contribute to the adaptability and fitness of these invasive species in the novel environments, as the gut microbiota can exhibit important functionalities and given its superior plasticity to changing conditions. We characterized the bacterial, fungal and parasite communities of M. sculpturalis sampled from native (Japan) and invaded regions (New York, USA and Marseille, France). Native, co-foraging bee species from Marseille (France) were additionally analyzed to assess the transmission of microbiota and pathogens between native and invasive bees. The gut microbiota of M. sculpturalis bees from the two invaded regions was highly similar and differed strongly from those obtained from the native region. In Marseille (France), one of the invaded regions, the microbiota of M. sculpturalis was significantly different from that of native co-foraging bees, yet native and invasive bees shared core amplicon sequence variants suggesting a potential for horizontal transmission of microbes and common environmental sources. M. sculpturalis bees examined in the present study did not harbor known bee pathogens. We proposed two hypotheses that might explain the similarity of the microbial community in bees from the two invaded regions and the absence of parasites: a common shift in gut microbiota in the invaded regions as a response to changed environmental conditions, or a founder effect in gut microbial composition caused by the introduction events.
In a final study, we provided a comprehensive characterization of the bacterial communities of the gut fractions and ovaries of V. velutina through a combination of 16S rRNA amplicon sequencing and culturomics. The bacterial community was dominated by highly specialized core lactic acid bacteria (Convivina and Fructobacillus), generalist core lactic acid bacteria (Lactococcus and Lactiplantibacillus), and Sphingomonas and Spiroplasma. The four sample types revealed distinct bacterial communities with similar richness and Shannon diversity. We isolated a total of 861 isolates including two species of the core symbiont Convivina: C. intestini, which was previously isolated from a bumble bee, and the novel species C. praedatoris. We analyzed both species through comparative functional genomics and biochemical assays to describe their metabolic capabilities within the hornet gut. Our results revealed that C. intestini was adapted towards amino acid metabolism and the novel species C. praedatoris was adapted towards carbohydrate metabolism
Tree species diversity effects on microclimate buffering, throughfall regulation and litter decomposition in young forest plantations
No full textKinetic Monte Carlo modeling of solution and surface-initiated polymerization
No full textRecente ontwikkelingen in polymerisatietechnieken hebben geleid tot de synthese van polymeermaterialen die geschikt zijn voor een breed scala aan toepassingen in verschillende sectoren. De synthese van poly(2-oxazoline)s, een interessante klasse van bio-geïnspireerde polymeren met hoge afstembaarheid, en de modificatie van de grensvlakeigenschappen van vaste oppervlakken door de synthese van oppervlaktegebonden polymeerketens zijn twee voorbeelden van geavanceerde complexe polymeermaterialen. De synthese van poly(2-oxazoline)s en aan het oppervlak gebonden polymeerketens zijn heel aantrekkelijk voor toepassingen zoals medicijn-, eiwit- en genafgifte die sterk afhankelijk zijn van een efficiënte aanpassing van de fysisco-chemische eigenschappen van deze polymeermaterialen. In deze context zijn zowel een gecontroleerd ontwerp van de polymeermaterialen als een volledige karakterisering van de producten van polymerisatieprocessen nodig om de efficiëntie van deze materialen in de gewenste toepassing te waarborgen. De ontwikkeling van geavanceerde computersimulaties en algoritmen maakt het mogelijk om de eigenschappen en prestaties van polymeermaterialen te optimaliseren tegen lage proceskosten, aangezien simulatiemodellen meestal experimentele tijd uitsparen. In dit proefschrift worden rekenmodellen ontwikkeld op basis van de implementatie van kinetische Monte Carlo algoritmen om de impact van procesvariabelen op de eigenschappen van poly(2-oxazoline)s en oppervlakgebonden polymeerketens te evalueren, gericht op de synthese van polymeermaterialen met verbeterde eigenschappen op een gecontroleerde, snelle en efficiënte manier
The presence, sources and transmission routes of important foodborne pathogens : salmonella during poultry and pig slaughter and Taenia saginata and Sarcocystis species in cattle carcasses and the environment
No full textPoultry meat, pork and beef are the most consumed meat products worldwide. Poultry and pigs are known carriers of Salmonella, while cattle are intermediate host of Sarcocystis spp. and Taenia saginata. The presence of these pathogens in meat are important sources of associated foodborne illness, which cause health and economic burden. An increasing knowledge of the presence, sources and transmission routes of these three pathogens during meat production are essential for improving control strategies. This PhD was conducted with the general aim of studying the presence, sources and transmission routes of Salmonella in poultry and pigs, Sarcocystis spp. and T. saginata in cattle and the environment
