Methyl ketones, used to provide scents to essential oils and flavoring in foods such as cheese, are naturally occurring compounds four in the aromatic evergreen plant known as rue. They have also been found in tomatoes and other plants, as well as in certain insects and microorganisms.
A sweet-smelling chemical compound primarily used in fragrances and flavoring is being studied for its potential as a clean and green biofuel.
Methyl ketones, used to provide scents to essential oils and flavoring in foods such as cheese, are naturally occurring compounds four in the aromatic evergreen plant known as rue. They have also been found in tomatoes and other plants, as well as in certain insects and microorganisms.
Methyl ketones can also be used as a blending agent for cleaner and greener diesel fuel.
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The E.coli bacterium also creates methyl ketons but only in very small amounts. However, two years ago, researchers at the United States Department of Energy’s Joint BioEnergy Institute engineered a strain of E. coli to convert glucose into significant quantities of methyl ketones.
“In our original effort, for methyl ketone production we made two major modifications to E. coli,” said Harry Beller, a JBEI microbiologist that led the study into this modfied E. Coli. “First we modified specific steps in beta-oxidation, the metabolic pathway that E. coli uses to break down fatty acids, and then we increased the expression of a native E. coli enzyme called FadM. These two modifications combined to greatly enhance the production of methyl ketones.”
Now, following further genetic modifications, Mr. Beller and his team have boosted their E. coli’s methyl ketone production 160-fold.
The modifications included balancing the overexpression of two other E. coli enzymes, fadR and fadD, to increase fatty acid flux into the pathway; consolidating two plasmid pathways into one; optimizing codon usage for pathway genes not native to E. coli; and knocking out key acetate production pathways.
The result was an E.coli strain that could produce a methyl ketone titer of 3.4 grams/liter after approximately 45 hours of fed-batch fermentation with glucose. This is about 40-percent of the maximum theoretical yield for methyl ketones.
“Although the improved production is still not at a commercial level in the biofuel market, it is near a commercial level for use in flavor and fragrances, where certain methyl ketones are much more highly valued than they would be in the biofuel market,”Mr. Beller said. “It may be possible for a company to sell a small percentage of methyl ketones in the flavor and fragrance market and use the profits to enhance the economic viability of the production of methyl ketones as biofuels. – Ecoseed Staff
