A successful winemaking process depends largely on the effective alcoholic fermentation of grape must with the yeast Saccharomyces cerevisiae. Dry yeast is added to the must, which ferments it under anaerobic conditions with sugar degradation and simultaneous ethanol production.

A high viability and activity of the yeast cells ensures a low or the desired residual sugar concentration and thus a low residual sweetness and a high ethanol concentration in the wine. Sometimes, however, fermentation stagnates. This can be due to the dry yeasts themselves, which are not sufficiently viable or vital despite rehydration prior to alcoholic fermentation, but also to unfavorable growth conditions, such as nutrient limitation. To avoid this so-called fermentation stagnation, it is essential to ensure sufficient viability and vitality of the cells before inoculation and during fermentation.

In this project, various aspects of this problem can be investigated in student projects together with project partners from the University of Hohenheim and a winery. This includes the aerobic cultivation of vital yeast cells under the restrictions imposed by the wine regulations and the process engineering for the process with the aid of on-line measurement data. A bioreactor with a volume of 1000 liters is available for this purpose. The development of assays to determine the vitality of S. cerevisiae is also part of the project. In addition, comparative fermentation tests with fresh, aerobically cultivated yeast in comparison to rehydrated yeast will be carried out. The fermentation processes must be investigated, as well as the sensory properties of the resulting wine. Some of the tests can be carried out directly at the winery.

Accounting for 11% of electricity demand, the process industry is one of the main consumers of electrical energy in Germany. The switch to a renewable electricity supply is therefore of crucial importance for the success of the energy transition. While electricity demand was previously covered according to demand, a variable renewable electricity supply requires processes to adapt flexibly to the electricity supply. This requires fundamentally new methods and processes to be developed and tested in real applications. In contrast to continuous processes, batch processes are still largely unexplored in terms of flexibilization. They are characterized by the fact that different units (stirrers, pumps, electric heaters, etc.) are started up and shut down in the course of a cycle in order to carry out different process steps one after the other.

The aim of the project is to make the processes more flexible. Bioprocess engineering is explicitly investigating the aerobic biodemonstrator for the production of citric acid with Aspergillus niger.

Aspergillus niger is a strictly aerobic filamentous fungus that forms black spores. In submerged cultivation, it is able to form either dispersed mycelia or pellets. It can also form a biofilm on surfaces. The different morphologies simultaneously influence the productivity of citric acid. For example, the productivity of citric acid can be increased by cultivating it on different carriers. The morphology that is formed in the process can be visualized using a confocal laser scanning microscope. Biofilm cultivation on carriers will be used to investigate the flexibilization of this batch process.

Special previous knowledge is not necessary, but some laboratory experience would be advantageous.

Plants produce a variety of interesting compounds, so-called secondary metabolites, which play a central role in ecological interactions, defense mechanisms and adaptive responses to environmental stimuli. The applications of these secondary metabolites range from pharmaceuticals to cosmetics and food additives and represent a source of bioactive compounds with great industrial potential. However, the growth rate of many plants is too slow for large-scale production with adequate product yields. In addition, their cultivation is often complex and expensive, which is why interest in plant cell cultures is increasing. This approach not only enables the cultivation of plant cells in closed bioreactors, but also has the advantage that certain cell types can be cultivated selectively. By transferring the differentiated tissue of a plant (e.g. the root or the stem) to an agar plate, the targeted induction of so-called callus cells is possible. These dedifferentiated, totipotent cells can then be used for growth in suspension cultures. Our research at the Chair focuses on the cultivation of different plant cell lines for the targeted production of specific secondary metabolites. Our projects provide hands-on laboratory experience and promote competence in experimental design, execution and analysis. English language skills are required and a background in life sciences or related disciplines is an advantage.

The production of concrete accounts for 8.6% of anthropogenic CO₂ emissions worldwide. Research is therefore being carried out into alternative ways of reducing CO2 emissions in concrete production. One biotechnological approach is the production of artificial sandstone using so-called biocement, which can be produced by various microorganisms. For example, ureolytic microorganisms are able to break down urea, which produces carbonate ions. In an alkaline environment and in the presence of calcium ions, calcium carbonate can be formed. Similar to classic cement, this process can be used to bind mineral particles, for example quartz sand, and thus improve soil properties. This process is being investigated at the Department of Bioprocess Engineering. The focus is on optimizing the production time of biocement. Practical work is possible in the cultivation of ureolytic microorganisms and the investigation of the kinetics of MICP. Special previous knowledge is not necessary.

Initial laboratory experience is desirable, but not a prerequisite.

Cyanobacteria are photoautotrophic and mostly biofilm-forming organisms, some of which are characterized by their special ability to fix atmospheric nitrogen. As cyanobacteria can then release the fixed nitrogen in a form that can be used by plants, they are suitable as a biological nitrogen fertilizer substitute. Biofilms of cyanobacteria can also release other growth-promoting substances or improve the water retention of soils. In this project, we are investigating the co-culture of nitrogen-fixing cyanobacteria with different plants, focusing on the following areas:

• Establishment of a co-culture in hydroponics to better understand the symbiosis of cyanobacteria and plants
• Immobilization of cyanobacteria on biodegradable materials
• Construction of new photobioreactors for the cultivation of cyanobacteria for use in the agricultural sector
• Increasing the water retention capacity of soils through phototrophic biofilms
• Co-cultivation in pot cultures

Cable bacteria are multicellular microorganisms that can transport electrons over distances of several centimetres. The filamentous bacteria have only been known for a few years, but have now been found in the sediment of numerous freshwaters and marine sediments. There they grow up to several cm deep into the sediment, whereby the cells oxidize sulphur compounds in the deeper, anoxic sediment. The electrons released are conducted along the filament into the oxic sediment layer, where the cells reduce oxygen. The unique metabolism of cable bacteria and their ability to conduct electrons over long distances makes them interesting production organisms for (electro)biotechnology. So far, however, there have been hardly any studies on this.

The Department of Bioprocess Engineering is investigating how the potential of these microorganisms can be harnessed. Practical work is possible in the field of cultivating cable bacteria, developing reactor systems and investigating possible applications as production organisms. No special previous knowledge is required.

The use of renewable raw materials (in german: nachwachsende Rohstoffe, NaWaRo) in biorefineries for the production of basic and fine chemicals has been part of current research for a long time. The issue has been intensified by the so-called plate-tank problem, according to which NaWaRo can be used either in biorefineries or as food. The Department of Bioprocess Engineering is currently working on exciting research projects that deal with the use of by-products or waste product streams such as municipal green waste. The focus here is particularly on the pre-treatment of biomass using mechanical processes and hydrothermal digestion in a pressure reactor with subsequent enzymatic hydrolysis in order to produce fermentable sugars from the structural carbohydrates it contains. These are used in subsequent process steps for the microbial production of industrially relevant basic and fine chemicals. In particular, this involves the production of organic acids and solvents.
Laboratory experience is desirable, but not a prerequisite for research work in this field.

Electrobiotechnology combines elements of classic biotechnology with electrochemical material conversions. The basis for this are electroactive microorganisms. These are able to release electrons directly or via mediators to an electrode or to absorb them from it. The former forms the basis of electricity generation using microbial fuel cells (MFC) and has been known for over a century. The absorption of electrons for microbial electrosynthesis (MES), on the other hand, has only been researched for a few years. The electrons provided at an electrode are taken up by electroactive organisms and used for the regeneration of reduction equivalents of the metabolic pathways. The electrons therefore act as an alternative energy source instead of sugars, which can increase the fermentation yield. The influence of an applied electrical potential on fermentations is being investigated at the Department of Bioprocess Engineering. The focus is on product yield and the development of new reactor systems.

The development of biofuels is becoming increasingly important in view of the depletion of oil reserves. The potential of butyric acid ethyl ester as a fuel has already been investigated and yielded promising results. As a result, the biological production of butyric acid ethyl ester with clostridia and yeast or bacteria in a self-sufficient reaction cascade is being investigated. Clostridia and yeast are to produce the products butyric acid and ethanol, which are esterified by the enzyme lipase. In the first step, the cultivation of clostridia for butyric acid production is carried out and optimized at the Department of Bioprocess Engineering. These cultivation conditions will be transferred to yeast cultivation in order to test the possibility of co-cultivating the two organisms. Co-cultivation will then be investigated on a small scale and in a bioreactor. Enzymatic catalysis of ester formation is also an important part of these experiments. In the further course, a two-phase system is to be established within the fermentation, whereby the ester is extracted into an organic phase. Experiments will also be carried out in this area of extractive fermentation.

Laboratory experience is desirable, but not a prerequisite for research work in this field.