Browsing by Subject "Mikroorganismen"

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Charakterisierung der Qualität von Blütenpollen in unterschiedlichen Regionen Baden-Württembergs
(2022) Friedle, Carolin Gertrud Maria; Hasselmann, Martin
Honey bees (Apis mellifera) collect nectar and pollen from plants to feed their brood. Pollen provides a wide range of nutrients, such as proteins and lipids, but also carbohydrates, vitamins and enzymes. Because of these ingredients, pollen is also attractive to humans and is used as a dietary supplement. However, honey bees collect pollen not only from wild plants, but also from flowering crops grown in agriculture. Accordingly, contamination from plant protection products can be found in bee pollen and bee bread. In order to get a deeper insight into the occurrence and distribution of pesticide residues during an entire season, a total of 102 daily pollen samples were collected from April to July 2018 using pollen traps in an orchard in southern Germany. Almost 90% of the pollen samples showed detectable levels of pesticide residues. A total of 29 pesticides were detected in the samples, with more than half being fungicides, followed by insecticides and herbicides. Maximum concentrations of up to 4500 ng/g could be measured at the end of April. Samples collected in early May and late June also showed high levels of pesticides. A general risk management was performed to assess the risk of the detected pesticide concentrations for honey bees. The microbial quality of bee pollen is highly dependent on its botanical and geographic origin, as well as climatic conditions and post-harvest processing steps by the beekeeper. If no processing steps such as freezing or drying follow after harvest, the growth of microorganisms can be promoted and the pollen quality can be influenced by negative side effects such as fermentation or the production of mycotoxins. Bacterial and fungal colonies can be determined both by culture-dependent methods such as colony counting on plates and by culture-independent methods such as 16-rRNA amplicon sequencing. Following the hypothesis that storage conditions influence the composition of microorganisms in bee pollen, freshly harvested bee pollen was stored for seven days in June 2018 and 2019 under defined conditions (cold, room temperature, warm) and analyzed by sequencing 16S and 18S PCR amplicons. The bacterial community varied slightly between the sites studied and showed no significant difference between the storage conditions. The fungal community showed significant differences both between the studied sites and between the different storage conditions. The dominant fungal genera in the pollen samples were Cladosporium, Aspergillus and Zygosaccharomyces. While Cladosporium was most dominant in freshly collected pollen and the percentage decreased during storage, Aspergillus and Zygosaccharomyces showed a significant increase especially under warm storage conditions. Other contaminants naturally produced by plants can also have negative impacts on human health. Pyrrolizidine alkaloids belong to a group of phytochemicals, of which more than 600 structures are known in around 3% of all flowering plants worldwide. PA are known to be able to cause both acute poisoning and chronic damage or cancer in animals and humans. In July 2019, pollen was collected at 57 locations in Baden-Württemberg and analyzed for 42 different PAs and their N-oxides in order to expand knowledge about PA contamination in pollen and to be able to estimate the risk of the concentrations. A total of 22 different PAs were detected in over 90% of all samples examined. Only 5% of the PA were obtained as PA from plants of Senecio sp. identified, while 95% of PAs with a botanical background are from Echium sp. and Eupatorium sp. could be identified. The maximum total concentration of PA per sample was determined to be 48,400 ng/g. According to the risk values calculated by the BfR, however, 42% of the samples represented an increased risk to human health.
The role of soil properties and fertilization management in pathogen defense and plant microbial interactions in the rhizosphere of lettuce (Lactuca sativa L.)
(2022) Windisch, Saskia Helen; Neumann, Günter
Soil microorganisms are involved in nearly all relevant soil processes and considered as key players in agro-ecosystems. This is particularly relevant for the rhizosphere which is created by the activity of plant roots with dynamic impact on microbial communities, their diversity and activity. Both, beneficial but also pathogenic plant-microbial interactions in the rhizosphere are driven by root exudates and other root-induced modifications in rhizosphere chemistry, which are highly variable in space, time, composition and intensity. The physicochemical properties of the rhizosphere are influenced by numerous external factors including nutrient availability, biotic and abiotic stress, soil properties or plant genotypic variation but the related consequences for plant-microbial interactions and the consequences for plant performance and health status are still poorly understood. In this context the present study was initiated to investigate (i) the influence of the soil type on root exudation and the composition of the rhizosphere solution (ii) their impact on interactions with soil pathogens and beneficial rhizosphere microorganisms and (iii) the effect of long-term fertilization strategies (organic vs. mineral fertilization), using lettuce (Lactuca sativa) as a well-characterized model plant for studies on plant-microbial interactions in the rhizosphere.