PURPLE YEAST: Reconstruction of anthocyanin pathway in yeasts: bottlenecks and challenges

The relative abundance of anthocyanins in the human diet and their potency against a range of chronic diseases have made them the subject of intense research in experimental and preventive medicine. However, the limited range of anthocyanins commercially available and the expense of pure preparations mean that most research is done with crude extracts of plants which are not standardised with respect to the particular anthocyanins they contain, nor the amounts of each anthocyanin in the extract. Beside the unique plant cell cultures recently developed for the stable production of a variety of anthocyanins (www.anthoplus.com) novel procedures for sustainable, high level production of diverse natural products in heterologous hosts like microorganisms show a high yield and can be up scaled to industrial production. Although all major genes coding for enzymes for the anthocyanins pathway were successfully expressed in yeast so far the multistep combinatorial synthesis of anthocyanins was only described for bacterial system starting from flavanone stage (Yan et al., 2005). The “purple yeast” project intensely focuses on strategies to genetically modify yeast (Saccharomyces cerevisiae) as innovative host for the combinatorial synthesis of various anthocyanins. Genetic modification strategies for heterologous gene expression and host bioengineering will be carried. Furthermore, challenges and bottlenecks as native degrading and/or competing proteins (e.g. b-glucosidases) and the described side activities of anthocyanin pathway proteins need to overcome (Yan et al., 2005, Martens et al., 2010; Schmidt et al., 2011). Finally, this strategies aim to establish a robust pre-industrial production system for new, pure anthocyanins