Philipp Benz
TU München
The need for a stable and sustainable source of energy is one of the grand challenges of our generation. Using lignocellulosic plant biomass as a renewable feedstock e.g. for biofuel production can contribute substantially on our way to meet this goal. However, for highest efficiency the utilization of all major constituent sugars is required. To this end, enzyme cocktails adapted to the individual composition of given feedstocks would be desirable as well as the engineering of downstream organisms able to ferment all major monosaccharides. In particular fungi are among the most promising tools to deconstruct plant cell wall polysaccharides due to their importance in global carbon recycling, but much remains to be learned about their enzyme production and sugar utilization mechanisms. A more profound knowledge of the fungal interaction with different plant substrates will therefore be highly informative for efforts to achieve a cost-effective biofuel production process.
In the presented work, we performed a systematic analysis of how Neurospora crassa perceives the presence of the three major plant-derived polysaccharides cellulose, xylan and pectin. The comparison of the individual responses allowed us to deduce fundamental knowledge on fungal adaptation strategies to the carbon composition in its environment. These included specific adaptations, such as a re-organization of the secretory pathway upon sensing of cellulose, but also commonalities, such as a set of enzymes that is cross-induced on all carbon-sources and could represent part of a polysaccharide scouting system.
Our study moreover revealed new factors involved in specific sugar utilization pathways. Here, we report on the identification and biochemical characterization of the first eukaryotic high-affinity MFS-type transporter for the uptake of galacturonic acid (GAT-1), which cannot be consumed by currently used yeast strains. To test its applicability in biotechnological sugar fermentation processes, GAT-1 was recombinantly expressed in yeast in combination with fungal galacturonic acid metabolism enzymes, to generate a transporter-dependent uptake and catalysis system into downstream products with high potential for utilization as platform chemicals: L-galactonate and meso-galactaric acid.
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