Currently, research in the Boles group is funded by:
BMBF: Metabolosome project - synthetic organelles
BMBF/FACCE SURPLUS: BioC4 project - isobutanol
BMEL: Alk2Bio project - heptane, octanol
EU: YEASTCELL project - aromatics
EU: CHASSY project – caprylic acid
Loewe/Hessen: MegaSyn project - PKS
DAAD: Xylose transporter project
The classical human interest into yeasts, lower unicellular eukaryotes, stems from their well known role in the preparation of wine, beer, and bread. In the last decades attention has focused on some additional functions for yeasts as well as scientific model organisms but also in their use for industrial or medical purposes. Today, yeasts cells are not only indispensable for fundamental research but belong to the most important organisms in industrial biotechnology.
In our group we are using yeasts to study general metabolic and regulatory processes, and are developing technologies to improve the applications of yeasts in biotechnology.
C5-Technology: Fermentation of pentose sugars with recombinant yeasts
During the last years we have successfully developed technologies ("C5-technology") to engineer yeast (Saccharomyces cerevisiae) strains for the fermentation of pentose sugars like xylose and arabinose (e.g. see patent on xylose isomerase). Agricultural and forestry residues are considered as a sustainable source for the fermentative production of biofuels and are rich in pentose sugars. Unfortunately, in contrast to glucose or sucrose yeast cells cannot normally ferment pentose sugars into biofuels like ethanol or butanol. We have used our proprietary C5-technology to construct recombinant industrial yeast strains fermenting efficiently both, glucose and pentose sugars (e.g. Demeke et al. 2013). The C5-technology was sold to the Swiss biotech company Butalco which in 2014 has been acquired by one of the world-leading yeast producers, the French company Lesaffre (for details click here). We are now working to further improve the C5-technology by developing tools to efficiently channel metabolites through the C5-sugar utilization pathways (BMEL-project ECO-FERM).
Engineering sugar uptake
Uptake of sugars and sugar derivatives in yeast is mediated by a large family of transporter proteins. Previously, we could show that deletion of at least 20 genes is necessary to completely block uptake of glucose into yeast cells (Wieczorke et al. 1999. The resulting so-called hexose transporter (hxt) null strain (EBY.VW4000) has become a valuable tool worldwide for the characterization of sugar transporters from other yeasts, fungi, plants, animals and even human cells (click here to see how the tool works (in chapter 2), and here to find examples).
Using the yeast hxt null strain we could recently convert glucose transporters into specific xylose transporters (Farwick et al. 2014). This work did not only significantly contribute to the understanding of sugar-transport mechanisms but, from an applied point of view, the new transporter versions are efficient tools for the cost-effective simultaneous co-fermentation of glucose-xylose mixtures in lignocellulosic hydrolysates (for details click here).
Currently we are working on the characterization and re-engineering of a variety of other sugar transporters.
Isobutanol and other biochemical compounds
Biobased chemicals are an essential part of a future biobased economy. White biotechnology will significantly contribute to the replacement of petrochemicals by biobased chemicals. New bioprocesses will be more economical as well as more ecological compared to their petrochemical counterparts.
We have constructed yeast strains producing isobutanol which is a much more promising biofuel than ethanol (Brat et al. 2012).Furthermore, we are engineering yeast cells for the production of cis,cis muconic acid which is a precursor e.g. in the production of nylon (Weber et al. 2012).
Within the collaborative project IPF – Integrative Pilzforschung (LOEWE-Schwerpunkt) and an R&D project financed by BASF we are searching for omega-functionalized fatty acids in fungi, are developing new pathways for synthesis of fatty acids and derivatives, and are establishing biotechnological production routes for these interesting chemical building blocks in yeast.
Moreover, in the Marie-Curie Initial Training Network project YEASTCELL our group is involved in the construction of recombinant yeasts for the production from sugars of valuable biomolecules derived from precursors of aromatic amino acids, like styrene.
Metabolite channeling and compartmentalization
Genetic engineering of yeast cells has already resulted in several industrial processes for the production of valuable compounds. However, in many cases production rates and yields must still be improved for economically viable processes. The efficiency of new metabolic pathways is often limited by factors such as diffusion, competing metabolic pathways or inhibitory intermediates.
We are developing new strategies to avoid these limitations. On one hand, strategies are being implemented to assemble pathways and transporters in artificial enzyme complexes in order to achieve efficient substrate channeling and thus to increase production rates (BMEL-project ECO-FERM). On the other hand, in the METABOLOSOM-project financed by BMBF we are establishing new concepts to deliver metabolic reactions and pathways into synthetic organelles.