Engineering Geobacillus for butanol production

The thermophilic organism Geobacillus thermoglucosidasius is a natural ethanol producer and, with ability to utilize C5 and C6 sugars present in biomass feedstock, is a candidate for commercial bioethanol production.  Thermophilic fermentations offer advantages over mesophilic processes, including decreased chance of contamination, lower product separation costs and simpler initial cellulose degradation.  However, butanol can be considered a superior biofuel to ethanol; it is more energy dense, has a lower vapour pressure allowing it to be mixed in higher proportions with gasoline, and is less corrosive and thus more suitable for distribution in existing fuel pipelines.  In this work, we aim to construct an efficient producer of butanol by introducing enzymes from the moderate thermophile Bacillus coagulans into G. thermoglucosidasius, diverting the existing ethanol pathway to butanol.  An important step for G. thermoglucosidasius to become a viable platform for the production of butanol, or indeed any chemical, is the alleviation of catabolite repression - a regulatory mechanism allowing cells to choose among several available carbon sources.  Sequential utilisation of substrates caused by catabolite repression with different energetic values can have a major effect on product yield, presenting problems for an industrial process relying on lignocellulose derived carbohydrate substrates.  HPr is a key player in catabolite repression, involved in a regulatory cascade that leads to binding of catabolite responsive elements (CRE) within promoters to exert repression.  HPr and CRE mutants have been created and assessed, with results indicating catabolite repression can be overcome, presenting the potential for developing an industrially viable platform.