S172: Engineering solvent tolerant microbes for biofuel production

For most compounds being considered as biofuel candidates, two aspects impede the efficiency of microbial production. One is their inherent solvent like nature that results in toxicity towards the microbe. Second is product inhibition due to intracellular accumulation. Therefore the efficiency with which the biofuel can be exported from the cell is likely to have significant influence on production titer. We investigated the role of efflux pumps in improving biofuel tolerance in Escherichia coli. We developed a simple but effective competition based strategy to select for pumps that bestowed tolerance against representative biogasoline, biodiesel and biojetfuel candidates. Heterologous pumps from marine organisms and microbes discovered from oil spill sites provided some of the best pumps for this function. Several pumps discovered using this strategy have never been characterized for biofuel tolerance, however not all biofuel candidates tested could be addressed using this pump based approach. For the candidates where effective pumps were found, expression of pumps also resulted in improved production levels. Optimization of expression systems will be key in maximizing the benefits from a specific pump in a fuel production strain. The strategy used in identifying specific pumps for biofuel tolerance can be implemented widely to discover gene targets for strain engineering.