Although sugars are the primary feedstock for the biological production of renewable fuels and chemicals, recent progress in the development of organisms that accumulate bio-oils (i.e. triesters of glycerol and fatty acids, FAs) and the abundance of glycerol- and FA-rich industrial byproducts make these carbon sources an attractive alternative. In addition to abundance, the higher degree of reduction and higher metabolic efficient of glycerol and FAs can support product yields significantly higher than those obtained from sugars. However, most industrial organisms metabolize glycerol and FAs only under respiratory conditions, which do not lead to the synthesis of fermentation products. We then have used synthetic and systems biology approaches to engineer the efficient synthesis of fuels and chemicals from these substrates (references below). Several native and heterologous fermentative pathways were engineered to function in E. coli under anaerobic and microaerobic conditions. Pathways for the efficient utilization of glycerol and FAs were engineered as well. Biofuels (ethanol, butanol, and hydrogen) and biochemicals (succinate, lactate, acetate, propionate, 1,2-propanediol, acetone, and isopropanol) were chosen as representative products to illustrate the feasibility of the proposed approach. Product yields in most cases exceeded those achieved with the use of sugars, clearly demonstrating the advantages of glycerol and FAs.

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