Fatty Acid-Producing Microbes for Generating Medium- and Long-Chain Hydrocarbons
New, renewable sources of transportation fuel are needed to meet continuing demand. While the main focus has been on biomass-derived gasoline alternatives such as ethanol and other short-chain alcohols, distillates with higher energy density such as diesel and jet fuel are required for the heavy transportation sector. Biodiesel is a biodegradable, clean-burning combustible fuel made of medium- to long-chain hydrocarbons that can be used in most internal combustion diesel engines. Current methods of making biodiesel involve transesterification of triacylglycerides (mainly vegetable oil). However, this process results in a heterogeneous mixture of fatty acid esters and unwanted side products such as glycerin and methyl and ethyl esters.
UW–Madison researchers have developed genetically modified E. coli that are capable of overproducing fatty acid precursors for medium- to long-chain hydrocarbons. The modified bacteria were transformed with exogenous nucleic acids to increase the production of acyl-ACP or acyl-CoA, reduce the catabolism of fatty acid products and intermediates, and/or reduce feedback inhibition at specific points in the biosynthetic pathway. The modified bacteria can be cultured in the presence of sugars to produce fatty acids. The fatty acid products formed during fermentation then can be separated from the fermentation media via a two-phase separation process or other method. The separated products can be used directly or as feedstock for subsequent reactions, including conversion to medium- and long-chain hydrocarbons.
- Total fatty acid production is increased nearly 10-fold, providing a greater amount of starting material for hydrocarbon production.
- Characteristics of resulting products, including branch points, saturation levels and carbon chain lengths, can be modified for different applications.
- Products may be highly homogeneous and relatively free from unwanted side products.
- System is suitable for continuous processing.
- Modified bacteria are recombinantly stable and growth-competent at 37°C.
- Other organisms such as yeast or additional Gram-positive bacteria may be used.
- Production of medium- and long-chain hydrocarbons for use as biofuels or specialty chemicals
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