Engineering of the yeast Saccharomyces cerevisiae for bioconversion of pectin-containing agro-industrial side-streams
Project acronym: YEASTPEC

- Elke Nevoigt, Jacobs University Bremen, Germany
- Wolfgang Liebl, TU München, Germany
- Peter Richard, VTT Technical Research Centre of Finland Ltd, Finland
- Isabel Sa-Correia, Instituto Superior Técnico, University of Lisbon, Portugal
- Johan Thevelein, GlobalYeast, Belgium

The yeast Saccharomyces cerevisiae has become a favorite organism in industrial biotechnology. The exceptional ease of targeted genetic engineering and the availability of an extensive toolbox for synthetic and systems biology have helped to overcome some of yeast's natural limitations in the context of consolidated bioprocessing of plant biomass. The first commercial processes for bioethanol production with lignocellulosic substrates have been established, and a robust engineered industrial strain with high performance for xylose utilization and lignocellulosic inhibitor tolerance represents the starting platform of YEASTPEC.

Besides lignocellulosic waste streams, cheap agro-industrial residues rich in pectin represent attractive substrates for industrial biotechnology which are largely unexplored so far. In Europe, particularly pulp from the sugar beet and fruit juice industry is available in huge amounts. Apart from glucose, sugar beet pulp hydrolysates are particularly rich in galacturonic acid (GalA) and arabinose. Both sugars cannot be naturally used by S. cerevisiae.

The YEASTPEC consortium is composed of researchers with complementary experience in metabolic engineering of industrial yeast, GalA, arabinose and glycerol catabolic pathways, yeast stress tolerance as well as enzymatic poly- and oligosaccharide hydrolysis. Within YEASTPEC, a robust industrial S. cerevisiae strain will be developed that is able to secrete enzymes for hydrolyzing the polysaccharides in sugar beet pulp and ferment all abundant monosaccharides, i.e. glucose, GalA and arabinose, into ethanol. One major novelty of our approach is that we address the inherent redox problem of the heterologous GalA catabolic pathways by co-feeding glycerol and appropriately engineering the glycerol catabolic pathway. Notably, glycerol is a major low-value by-product of current biodiesel production and thus also available in huge quantities. The industrial strain will also be engineered for improved process robustness during industrial fermentation of sugar beet pulp hydrolysates.