Thomas Hirth

Probing the contractile vacuole as Achilles’ heel of the biotrophic grapevine pathogen Plasmopara viticola

The causative agent of Grapevine Downy Mildew, the oomycete Plasmopara viticola, poses a serious threat to viticulture. In the current work, the contractile vacuole of the zoospore is analysed as potential target for novel plant protection strategies. Using a combination of electron microscopy, spinning disc confocal microscopy, and video differential interference contrast microscopy, we have followed the genesis and dynamics of this vacuole required during the search for the stomata, when the non-walled zoospore is exposed to hypotonic conditions. This subcellular description was combined with a pharmacological study, where the functionality of the contractile vacuole was blocked by manipulation of actin, by Na, Cu, and Al ions or by inhibition of the NADPH oxidase. We further observe that RGD peptides (mimicking binding sites for integrins at the extracellular matrix) can inhibit the function of the contractile vacuole as well. Finally, we show that an extract from Chinese liquorice (Glycyrrhiza uralensis) proposed as biocontrol for Downy Mildews can efficiently induce zoospore burst and that this activity depends on the activity of NADPH oxidase. The effect of the extract can be phenocopied by its major compound, glycyrrhizin, suggesting a mode of action for this biologically safe alternative to copper products.

Investigations of a catalyst system regarding the foamability of polyurethanes for reactive inkjet printing

Reactive inkjet printing is a promising manufacturing tool for a variety of materials. Combined with polyurethane chemistry, it can be used to build micro-scale foams. Waterblown polyurethane foams based on polyethylene glycol 200 (PEG200), glycerol ethoxylate (Star-PEG) and 1,6-hexamethylene diisocyanate (HDI) were used to prepare the foams. The system was catalyzed using iron(III) chloride, dibutyltin dilaurate (DBTL), diazabicyclo octane (DABCO) and bis(2-dimethylaminoethyl) ether. The influence of iron(III) chloride and DBTL were investigated by means of creamtime measurements. Catalyst stability was tested for 32 hours within the formulation. Furthermore, the foam formation was observed placing microliter droplets on top of each other using thermographic recordings and FT-IR spectroscopy. The materials tested give inkjet printable fluids that can be used to produce polyurethane foams. Heat evolution due to the exothermic urethane and urea formation was observed within the droplets. FT-IR spectra confirmed the urethane and urea formation.

Pressurized extraction of unsaturated fatty acids and carotenoids from wet Chlorella vulgaris and Phaeodactylum tricornutum biomass using subcritical liquids

The objective of this study was to investigate the extraction of lipids, for example, mono‐ and polyunsaturated fatty acids (PUFA) as well as carotenoids, from wet microalgae biomass using pressurized subcritical extraction solvents, which meet the requirements of food and feed applications. To demonstrate the effect of the solvent and temperature on the lipid yield, we chose two microalgae species, viz. Chlorella vulgaris and Phaeodactylum tricornutum, differing in their biochemical composition fundamentally. In case of P. tricornutum, ethanol showed the highest fatty acid yield of 85.9% w/w. In addition to eicosapentaenoic acid (EPA), the ethanolic extracts contained exceptional amounts of fucoxanthin (up to 26.1 mg/g d. w.), which can be beneficial to protect unsaturated fatty acids from oxidation processes and in terms of human nutrition. For C. vulgaris, a fatty acid yield of 76.5% w/w was achieved from wet biomass using ethyl acetate at 150°C. In general, an increase in the extraction temperature up to 150°C was found to be important in terms of fatty acid yield when extracting wet microalgae biomass. The results suggest that it is possible to efficiently extract both fatty acids and carotenoids from wet microalgae by selecting suitable solvents and thus circumvent energy‐intensive drying of the biomass.