Interdisciplinary PhD projects 2023

NovoStimAct – Plant Biostimulant Activity of Novel Bacterial Biosurfactants

Sandra Bredenbruch (Coordinator), INRES - Molecular Phytomedicine, Universität Bonn
Nina Stadler, Bioorganic Chemistry, HHU Düsseldorf

Funding period: 01.05.-31.10. 2023

In the Mini-Project NovoStimAct, two species of the genera Rhodococcus and Sporosarcina were evaluated for their potential to produce surface-active agents, so-called biosurfactants (BSFs). The amphiphilic metabolites were further analysed structurally (partner 2) and for their plant biostimulant activity (partner 1).  
We could prove that fuel and glucose triggered the synthesis of surface active metabolites in the Rhodococcus species, but not in the Sporosarcina species. Fuel as carbon source during bacterial cultivation induced the biosynthesis of BSFs very quickly, but also severely impaired a successful BSF extraction. BSF biosynthesis was also induced in the presence of glucose, but the surface activity was less intense even after doubling the cultivation period. Although fuel was quickly emulsified in culture with the Rhodococcus bacterium, no culture supernatant showed emulsion capacity and none had an effect on seed swelling. Mimicking seed application by a brief incubation of seeds in either bacterial cells or their crude metabolite mixture resulted in a faster germination, often accompanied by higher germination rate in soil. More detailed analysis of the plant phenotype under axenic conditions revealed a significant increase in root growth for several crop plants including wheat, maize and sugar beet. This is an important finding towards bio-derived agents in a sustainable agriculture. 

Abbildung: Joana Pohlentz

ReCHARM - Recycling of Ustilago maydis Cell Debris into Biochar for Soil Amelioration

Katharina Miebach (Coordinator), AVT-Biochemical engineering, RWTH Aachen
Joana Pohlentz, Microbiology, HHU Düsseldorf
Alexandra Brautlacht, Technology of energy raw materials, RWTH Aachen

Funding period: 01.04.-30.09.2023

The project aim was to enhance the sustainability and economic viability of biotechnological processes involving Ustilago maydis. One key objective was the development of a sustainable enzymatic cell disruption method to release valuable intracellular products while avoiding the use of harsh chemicals. The other key objective was to create a circular process by growing U. maydis on agricultural side streams and recycling waste from the U. maydis cultivations through pyrolysis to produce biochar for soil amendment, thereby generating new revenue.  
Work package 1 (WP1) developed a gentle method for cell lysis to release intracellular products without affecting their properties. A red fluorescent reporter (mKate2) was introduced for monitoring cell disruption, and an inexpensive enzyme mixture (VinoTaste® Pro) was tested for its ability to force cell lysis in the culture broth. The results showed that adding VinoTaste® Pro to U. maydis cultures released the reporter with an efficiency of around 50% compared to the standard cryo milling treatment. In parallel, genetic modifications to enhance U. maydis fragility were tested, but these modifications alone were not sufficient for efficient cell lysis. In WP2, we investigated the potential of plant waste streams as carbon sources for U. maydis to produce triglycerides. While grounded corn leaves and cobs supported U. maydis growth, they did not lead to high triglyceride production. Hydrolyzing the plant biomass in a preceding step provided sufficient carbon for growth, along with surplus sugars for triglyceride production. However, the triglyceride yield was still lower compared to pure sugar fermentations. Capacitance measurement was implemented to monitor microbial biomass during cultivation in turbid media, proving to be a feasible online monitoring tool without interfering with triglyceride production. WP3 investigated the volatilization behavior of U. maydis through thermogravimetric analysis (TGA) to assess the potential of biochar from U. maydis residuals. TGA experiments revealed a promising yield expectancy of approx. 30%, indicating significant carbon fixation. Control analysis using chitin, a major fungal component, suggested that this polymer is only a minor constituent of the residuals which rather resembled volatilization patterns observed in lignocellulosic plants. Microscope pictures of the produced biochar showed limited pores or surface structures, crucial for biochar effectiveness. Further experiments to analyze the surface area of the biochar are deemed essential. Still, the TGA results highlight the promising characteristics of biochar production from fungi like U. maydis.