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How Engineered Cells Could Lead To More Efficient Biofuel Production

With dwindling gasoline reserves, the search for more renewable energy sources has been ongoing for quite some time, with scientists looking at the possibility of heavy alcohols like isobutanol as alternative sources of energy. Apart from being more compatible with current gasoline based infrastructure, they also provide more energy when compared to ethanol. However, before the use of isobutanol becomes practical, there is a need for scientists to figure out a way of producing it from renewable resources on large scale.

Biologists and chemical engineers from MIT have come up with a way to drastically increase isobutanol production in yeast. The scientists engineered the yeast such that isobutanol synthesis occurs entirely in mitochondria (the cell structures which produce energy and host numerous biosynthetic pathways). Through the use of this approach, the scientists achieved a 260% boost in isobutanol production.

Though it is still on a small scale and not yet matching the levels required in industrial use, the progress so far registered points to a bright future as concerns engineering isobutanol and other useful chemicals. According to the authors of this approach that appeared in Nature Biotechnology on 17th February, the efforts are not only being directed towards isobutanol but also other bio chemicals that the scientists believe could be better suited for the task than cytosol found in the yeast cells.

The report is a collaborative effort between Gerald Fink, a biology professor at MIT and Gregory Stephanopoulos, a chemical engineering professor at the same institute. Jose Avalos who is a postdoc at MIT was the head of the team.

Traditionally, isobutanol had always been reduced from yeast during wine production because it was found the damage the flavor of the beer and wine but “now there is a drive to make it for fuel and related chemical uses” according to the lead author Jose Avalos.

According to the authors, isobutanol production from yeast involves a number of reactions that occur in two separate cell locations. The process of synthesis starts with pyruvate, a molecule generated in plenty glucose and other sugars. Pyruvate is then moved into the mitochondria from where it enters many different pathways, among which is on that leads to the production of valine. Alpha KIV (which is a precursor) is manufactured in the first stage of producing isobutanol. The two components alpha KIV and valine can be moved to the cytoplasm and turned into isobutanol by a given set of enzymes.

The research by the authors of this paper however took a different approach from the one described above. Instead, the second phase was moved (this phase normally takes place within the cytoplasm) into the mitochondria. They achieved this through engineering the enzymes of the metabolic pathway to show a tag usually located on the mitochondrial protein and in the process re-directing the cell thus sending the enzymes to the mitochondria.

This relocation of the enzyme led to a boost in the isobutanol generation by 260%. Not only did the quantities of isobutanol go up, the relocation also increased the production of isopentanol and 2-methyl 1-ethanol (related alcohols) by 370% and 500% respectively. Though there is no concrete explanation yet for the surge in the production of these alcohols, the researchers linked the increase to the clustering of enzymes which most likely leads to the occurrence of the reactions.

The second possible explanation according to Avalos is that the movement of the second phase into the mitochondria eases the process of the enzyme snatching up the little supply of precursors before they are moved to a different pathway.

At the moment though, the researchers are looking for means to further increase isobutanol production and reduce the ethanol production that as of now is the main by product of the process of sugar breakdown in yeast. The main concern at the moment is reducing the ethanol produced from yeast which will pave the way for increased isobutanol yields.

So far the scientists have produced some good work but more is yet to be seen as we are yet to find out if the approach will produce enough yields for commercial and large scale use. As of now, the future looks bright and we all hope that this could be the best solution to our ever increasing energy needs.


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