(190e) Engineering a New Microbial Production Platform for Fuels and Chemicals

The prevailing biomass technology relies on a complete hydrolysis of cellulose to its monomer sugars before the fermentation step, entailing large amounts of enzymes.  The cost of enzymes and slow hydrolysis step are widely recognized as important barriers for biofuel production. We have developed novel microbial catalysts capable of utilizing cellulose partial hydrolysis products, cellobiose or larger glucose oligomers (collectively known as cellodextrin). These microbial strains transport cellodextrin inside the cells, where they are subsequently metabolized and converted to biofuel. The new production scheme has several important advantages. 1.) Directly use of cellodextrin eliminates the need for complete hydrolysis. As a result, exogenous beta-glucosidase is no longer needed, generating significant cost savings.  2.) Once inside the cells, cellodextrin can be metabolized via a more energetically favorable mechanism, phosphorolysis. 3.)  Transporting sugar oligomers inside the cells for intracellular metabolism bypasses the catabolite repression. Consequently, glucose oligomers and xylose can be simultaneously converted to biofuel molecules, reducing the fermentation time thereby enhancing productivities. 4.)  The new technology reduces the burden of contamination as glucose concentration in the fermentation tank can be kept low.

In this presentation, we discuss the discovery of cellodextrin transporters from bacterial origin.
 We show that the newly discovered transporters can be used to engineer new types of microbial catalysts that access partial hydrolysed cellulose and assimilate cellodextrin directly. We present a first successful E. coli biocatalyst that metabolizes cellodextrin through an alternative but more energy- efficient phosphorolytic mechanism. Finally, we show that the transport of cellodextrin and its subsequent intracellular metabolism masks the presence of glucose and allows to evade catabolite repression, thus cellodextrin and xylose were simultaneously utilized.  In one example, simultaneous conversion of cellobiose and xylose led to a 100% increase in productivity, demonstrating the potential of this new microbial platform in biofuel production.