Microbial production of fuels and chemicals provides opportunities for replacing conventional production processes, which are based on chemical synthesis from non-renewable raw materials or on labour- and capital-intensive extraction from animal or plant tissues. Aeons of evolution, in which astronomical numbers of microorganisms competed for scarce resources, have optimized and streamlined the thousands of biochemical conversions in their cells for growth in specific natural environments. The resulting metabolic diversity, represented by many millions of microbial species, offers a great potential for developing novel microbial conversions of renewable substrates to products. Major advances in (recombinant) DNA technology have enabled the engineering of several microorganisms into efficient production platforms, which can be further modified for the production of a wide range of fuels and chemicals. For high-volume products based on microbial fermentation, such as transport fuels and commodity chemicals, the use of substrate can comprise up to 70% of the total product costs. These high substrate costs make a high product yield on the substrate essential for economic viability.

CRISPR/Cas9 is a novel Swiss Army Knife in the field of synthetic biology. The thesis of Harmen van Rossum (Biotechnology/TNW) shows that this tool enables rapid genetic modification of baker’s yeast; six genetic changes could be introduced within one week – previously this could easily take a few months.
The goal of the PhD project was to optimise yeast as a cell factory for the production of a wide variety of compounds, like jet fuels and diesel replacements from renewable sources. An important precursor for such products is acetyl-CoA, a universal building block that also participates in many metabolic and physiological processes. However, its synthesis in yeast is suboptimal, requiring more sugar than necessary. Competition with fossil-based production processes is challenged by such inefficiencies. The thesis showed that this can be addressed by a combination of synthetic biology, laboratory evolution and genetic engineering. Besides replacing the native acetyl-CoA production pathway in baker’s yeast by more efficient routes from other organisms, it was also demonstrated that the direction of an important shuttle system (the carnitine shuttle) could be reversed. Such changes are key to improve acetyl-CoA production from sugars. Harmen’s PhD project was part of the BE-Basic program and in close collaboration with DSM (Delft) and Amyris (Emeryville, CA, USA). Currently, Harmen van Rossum works as a scientist at the biotech company Zymergen (Emeryville, USA).