Industrial microbiology: Fuelling the renewable revolution

Nature Reviews Microbiology 8, 158-159, (March 2010) [doi:10.1038/nrmicro2328]

The production of fuels and other high-value chemicals through microbial fermentation has the potential to provide a sustainable alternative to petrochemicals. Publishing in Nature, Jay Keasling and colleagues now describe the engineering of Escherichia coli to produce structurally tailored fatty acids and their derivatives from simple sugars and plant-derived biomass.

Fatty acids, a primary metabolite of bacteria, are energy-rich molecules that can provide the basis for a range of fuels and chemicals. Keasling and colleagues engineered a strain of E. coli in which they effectively short-circuited the negative-feedback loop that regulates fatty acid biosynthesis, increasing the yield of fatty acids sixfold to 1.2 grams per litre. Although fatty acids are useful, directly compatible chemicals such as biodiesel and fatty alcohols are in greater demand. By introducing additional genes to modify the fatty acids produced, the authors were able to engineer E. coli strains grown on glucose and ethanol to produce fatty acid ethyl esters (FAEEs), a component of biodiesel, and fatty alcohols at 400 milligrams per litre and 60 milligrams per litre, respectively. The chain lengths of these fatty acid derivatives could be regulated by introducing genes encoding various plant thioesterases. Furthermore, following the introduction of genes encoding a pyruvate decarboxylase and an alcohol dehydrogenase, the need to provide ethanol in the growth medium could be overcome.

Using microbial fermentation to produce such fuels and chemicals directly from cellulosic plant biomass could circumvent the need for the costly biochemical processing that is currently required to release useable sugars. To address this issue, Keasling and colleagues introduced genes encoding hemicellulases into the FAEE-producing E. coli strain, enabling growth on hemicellulose.

This study suggests that the ability to rationally engineer microorganisms to produce biofuels from plant biomass at commercially viable yields could soon be realized.

Andrew Jermy