Researchers at the UCLA Henry Samueli School of Engineering and Applied Science have genetically modified Escherichia coli, a bacterium often associated with food poisoning, to produce unusually long-chain alcohols that could be used as fuel.
‘Previously, we were able to synthesise long-chain alcohols containing five carbon atoms,’ said James Liao, UCLA professor of chemical and biomolecular engineering. ‘We stopped at five carbons at the time because that was what could be naturally achieved. Alcohols were never synthesised beyond five carbons. Now, we've figured out a way to engineer proteins for a whole new pathway in E. coli to produce longer-chain alcohols with up to eight carbon atoms.’
The new protein and metabolic engineering method was developed by Prof Liao and his research team.
Longer-chain alcohols, with five or more carbon atoms, are easy to separate from water and are less volatile and corrosive than the commercially available biofuel ethanol. Ethanol, most commonly made from corn or sugarcane, contains only two carbon atoms.
Organisms typically produce a large number of amino acids, which are the building blocks of proteins. In their research, Prof Liao's team examined the metabolism of amino acids in E. coli and changed the metabolic pathway of the bacterium by inserting two specially coded genes.
One gene, from a cheese-making bacterium, and another, from a type of yeast often used in baking and brewing, were altered to enable E. coli's amino acid precursor, keto acid, to continue the chain-elongation process that ultimately resulted in the longer-chain alcohols.
Synthetic metabolism enabled by protein engineering: Genes inserted into E. coli bacteria encode designed proteins (ribbon- and string-shaped structures) that convert an amino acid precursor (gray and red molecule) into alcohols that could be used as biofuels
‘We showed that we are not limited by what nature creates. From an energy standpoint, we wanted to create larger, longer-chain molecules because they contain more energy. This is significant in the production of gasoline and even jet fuel.’
Though this new frontier of biofuels production from organisms has the potential to address significant issues in global warming, the scientific significance of successful genetic modification could also mean great benefits beyond the environment.
‘We used E. coli because the genetic system is well known, it grows quickly and we can engineer it very easily,’ said Kechun Zhang, a UCLA postdoctoral researcher. ‘But this technique can actually be used on many different organisms, opening the door to vast possibilities in the realm of polymer and drug manufacturing.’
The study was funded in part by the UCLA Department of Energy Institute for Genomics and Proteomics.