Plant oil biorefineries provide fatty acid derived products, such as biodiesel, but accumulate large amounts of crude glycerol as a side stream. Upgrading this glycerol increases the economic value derived from the plant oil, increases the carbon efficiency of the biorefinery and decreases the environmental impact of the process. Microbial conversion is one of many possible approaches to valorize crude glycerol by turning it into other valuable products. Among the possible microbial cell factories for this purpose, the yeast Yarrowia lipolytica has a particularly high potential. It has very flexible metabolic activities allowing it to produce many different products, such as citric acid and various sugar alcohols. Choice of the strain and varying the process conditions allow to tune the metabolism to favor one product over the others.

Research questions:
Y. lipolytica can also form biofilms on suitable solid surfaces by secreting and embedding themselves in an extracellular polymeric substance (EPS). The biofilm formation of Y. lipolytica is quite an interesting ability as it potentially increases the tolerance against stresses and allows easy biomass reusability in bioprocesses. However, it is unknown so far, how changing the growth mode from planktonic (free cells) to biofilm state could affect the metabolism of this yeast. The main question of this project is to analyze the metabolic reactions of Y. lipolytica to biofilm formation and to evaluate, if biofilm formation can be a game-changer for microbial chemical production with this cell factory. However, the project also addresses fundamental questions of biofilm formation of this yeast as how and when biofilms are formed. Such questions have not been addressed before from a bioprocess engineering point of view – to the best of our knowledge.

In a first step biofilm formation of the yeast shall be characterized. To this end, different solid support materials and different process conditions will be compared. The most conducive supports and conditions will then be used to establish batch and continuous cultures of the yeast to compare the metabolite patterns of planktonic cells with biofilm states. Finally, the upscaling experiment will be addressed to study the product formation from different modes of cultivation using bioreactors.

This project will take a total of three yearsin the University of Natural Resources and Life Sciences (BOKU) – in the Institute of Microbiology and Microbial Biotechnology under supervision of Assoc. Prof. Dr. Michael Sauer.

Each experiment, including (1) the study of the effect of solid support, (2) the effect of cultivation medium, (3) the effect of biofilm formation on the metabolite pattern of Y. lipolytica, and (4) upscaling experiment, would take approximately 9 – 12 months (with overlapping between topics) to complete.