Renewable biofuel oozes from reprogrammed microbes

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A population of Arizona State University's fatty acid-secreting cyanobacteria microbes

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It seems like every day, a new way of producing biofuel is being discovered. Within the past few years, we’ve reported on technology that harvests biofuel from garbage, booze, crop waste, carbon dioxide and wood-munching marine isopods. Now, Arizona State University has announced a new development in the harvesting of biofuel from cyanobacteria microbes - ASU researchers Xinyao Liu and Roy Curtiss have genetically engineered bacteria that literally ooze the stuff out of their skins.

Cyanobacteria, also known as blue green algae, photosynthesize sunlight into energy-rich fatty acid oil, ideal for biofuel production. The challenge, as with many biofuel sources, has been in finding a way of economically getting at it. When we last reported on Liu and Curtiss, they had found a way of genetically programming the single-celled microbes to self-destruct, thus releasing their precious contents. They have now engineered cyanobacteria that continuously secret the oil through their skins, thus allowing for higher yields, and doing away with the need to be constantly producing more bacteria.

Liu started by producing cyanobacteria carrying the enzyme thioesterase, that clips the bonds that bind the fatty acid to more complex carrier proteins. This allowed for more oil to accumulate within the microbes, to the point where it could no longer be contained.

To make the process more efficient, he then modified two layers of the cyanobacteria’s cellular envelope (skin) so that the fatty acid could get out more easily. Once out, it precipitates to the surface of the bacteria’s liquid environment, where it forms an easily-harvested whitish residue.

Finally, the team added genes that caused overproduction of fatty acids, while also removing cellular pathways that weren’t essential to the microbe’s survival. The result was a cyanobacteria that devoted all its resources to oil production and basic survival.

So, what makes cyanobacteria a good source of biofuel? For one thing, it gets its energy from the sun, as opposed to the fuel-consuming manmade heat required by some other sources. It also doesn’t take up valuable cropland, that could otherwise be used for growing food - look no further than the current criticism of large cornfields that are devoted solely to biofuel production.

And hey, what could be greener than blue-green algae?

Liu and Curtiss’ full report was recently published in Proceedings of the National Academy of Sciences.

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