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A little while ago, we covered the idea of using photovoltaic materials to drive enzymatic reactions in order to produce specific chemicals. The concept is being considered mostly because doing the same reaction in a cell is often horribly inefficient because everything else in the cell is trying to regulate the enzymes, trying to use the products, trying to convert the byproducts into something toxic, or up to something even more annoying. But in many cases, these reactions rely on chemicals that are only made by cells, leaving some researchers to suspect it still might be easier to use living things in the end.
A new paper in Nature Catalysis may support or contradict this argument, depending on your perspective. In the end, the authors of the new paper re-engineer standard brewer's yeast to produce molecules that can be used as fuel for internal combustion engines. The full catalog of changes they have to make is a bit mind-numbing and most achieve a small, incremental increase in production. The end result is a large step forward toward biofuel production, but the effort involved is intimidating.
Brewer's yeast, as the name implies, can already produce a biofuel: alcohol. But ethanol isn't a drop-in replacement for many current uses, which raises questions about its overall utility. If we have to re-engineer both our engines and our infrastructure in order to use it to replace fossil fuels, then there's not much space for a smooth transition away from gasoline and other liquid fuels.
But yeast obviously produce a lot of chemicals in addition to ethanol, and some of them are much more similar to our hydrocarbon fuels. Most liquid fuels are short strings of carbon atoms with hydrogen linked to each carbon. That mostly describes the building blocks of fats, which differ from hydrocarbon fuels in that one of the carbon atoms at the end of the string is hooked up to a couple of oxygens. These molecules also have a longer string of carbon atoms than a typical fuel—18-24 carbon atoms, rather than six to 12. But living things produce them in abundance, since they're used to make membranes and store energy.
Still, as challenge go, this one sounds relatively simple: get the cell to make shorter versions of what it's already making, then eject those into the media the cells are growing in. We can simply harvest the media, separate out the fuel molecules, and then let the yeast start afresh.
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