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
NIH: Human glucose transporters - drug
BMBF: PRO-SUGAR - pectin to polyhydroxy acids
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.
Butanol and aromatic 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. In line with this, we are constructing yeast strains producing isobutanol or n-butanol which are much more promising biofuels than ethanol (Brat et al. 2012; Schadeweg and Boles 2016). 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. 2017). Moreover, in the EU-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 aromatic amino acids, like styrene, cinnamic acid and cinnamyl alcohol.
Short-chain fatty acids, higher alcohols and polyketides
Short-chain fatty acids are high-value constituents of cosmetics, active pharmaceutical ingredients, antimicrobial substances, aromas or soap. To date, it has only been possible to extract them from crude oil by chemical means or from certain plants, such as coconut, using a complex process. We together with the research group led by Professor Martin Grininger have now succeeded in producing such fatty acids in large quantities from sugar or waste containing sugar with the help of yeasts. The process is simple and similar to that of beer brewing (Gajewski et al. 2017).
We are currently developing these technologies further and in different directions. The aim of the “Chassy" project funded by the European Commission is to scale up the technology for industrial use. In addition, the LOEWE project “MegaSyn" financed by the Federal State of Hesse focuses on the production of further chemical compounds through the modification of polyketide synthases. And in the “Alk2Bio" project funded by the Federal Ministry of Food and Agriculture yeasts are being enhanced in such a way that they produce 1-octanol and heptane as advanced biofuels from short-chain fatty acids.
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. 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 by Goethe-University Frankfurt 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 and by improving the uptake of xylose into the yeast cells (Farwick et al. 2017).
Sugar uptake and human glucose transporters
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). Currently we are working on the characterization and re-engineering of a variety of other sugar transporters, like a new-family of polyol transporters (Jordan et al. 2016) and human glucose transporters (see Wieczorke et al. 2003).
Synthetic organelles 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. 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 (Reifenrath et al. 2016).