Microbes reprogrammed to ooze oil for renewable biofuel (w/ Video)

Microbes reprogrammed to ooze oil for renewable biofuel
Photosynthetic microbes called cyanobacteria offer attractive advantages over the use of plants like corn or switchgrass, producing many times the energy yield with energy input from the sun and without the necessity of taking arable cropland out of production. Credit: Biodesign Institute, Arizona State University

Using genetic sleight of hand, researcher Xinyao Liu and professor Roy Curtiss at Arizona State University's Biodesign Institute have coaxed photosynthetic microbes to secrete oil—bypassing energy and cost barriers that have hampered green biofuel production. Their results appear in this week's advanced online issue of the Proceedings of the National Academy of Sciences.

The challenges of developing a renewable biofuel source that is competitive with the current scalability and low-cost of petroleum have been daunting. "The real costs involved in any biofuel production are harvesting the fuel precursors and turning them into fuel," said Roy Curtiss, director of the Biodesign Institute's Center for and Vaccinology and professor in the School of Life Sciences. "By releasing their precious cargo outside the cell, we have optimized bacterial metabolic engineering to develop a truly green route to biofuel production."

Photosynthetic microbes called cyanobacteria offer attractive advantages over the use of plants like corn or switchgrass, producing many times the energy yield with energy input from the sun and without the necessity of taking arable cropland out of production.

Biodesign Institute researcher Xinyao Liu explains the advantages of genetically optimizing cyanobacteria to secrete high-energy fatty acids for renewable biofuel production. Credit: Jemal Leonard, Biodesign Institute, Arizona State University

Lead author Xinyao Liu and Curtiss, applied their expertise in the development of bacterial-based vaccines to genetically optimize cyanobacteria for biofuel production. Last year, they were able to modify these , priming them to self-destruct and release their lipid contents. In the group's lastest effort however, the energy-rich fatty acids were extracted without killing the cells in the process.

"In China, we have a saying," Liu says. "We don't kill the hen to get the eggs." Rather than destroying the cyanobacteria, the group has ingeniously reengineered their genetics, producing mutant strains that continuously secrete fatty acids through their cell walls. The cyanobacteria essentially act like tiny production facilities.

Liu realized that if cyanobacteria could be cajoled into overproducing fatty acids, their accumulation within the cells would eventually cause these fatty acids to leak out through the cell membrane, through the process of diffusion. To accomplish this, Liu introduced a specific enzyme, known as thioesterase, into cyanobacteria.

The enzyme is able to uncouple fatty acids from complex carrier proteins, freeing them within the cell where they accumulate, until the cell secretes them. "I use genes that can steal fatty acids from the lipid synthesis pathway," Liu explains noting that thioesterase acts to efficiently clip the bonds associating the fatty acids with more complex molecules. This use of modified thioesterases to cause secretion of fatty acids was first described for Escherichia coli by John Cronan of the University of Illinois more than a decade ago.

A second series of modifications enhances the secretion process, by genetically deleting or modifying two key layers of the cellular envelope—known as the S and peptidoglycan layers—allowing fatty acids to more easily escape outside the cell, where their low water solubility causes them to precipitate out of solution, forming a whitish residue on the surface. Study results show a 3-fold increase in fatty acid yield, after genetic modification of the two membrane layers.

To improve the fatty acid production even further, the group added genes to cause overproduction of fatty acid precursors and removed some cellular pathways that were non-essential to the survival of cyanobacteria. Such modifications ensure that the microbe's resources are devoted to basic survival and lipid production.

Liu emphasizes that the current research has moved along at a lightening clip, with only about 6 months passing from the initial work, through production of the first strains—a fact he attributes to the formidable expertise in the area of microbial genetic manipulation, assembled at the Biodesign Institute. "I don't think any group would have the capacity to do this as fast," he said.

Professor Roy Curtiss agrees, noting that "the seminal advance has been to combine a number of genetic modifications and enzyme activities previously described in other bacteria and in plants in the engineered cyanobacteria strains along with the introduction of newly discovered modifications to increase production and secretion of . The results to date are encouraging and we are confident of making further improvements to achieve enhanced productivity in strains currently under construction and development. In addition, optimizing growth conditions associated with scale-up will also improve productivity."

The team, which includes researchers Daniel Brune and Wim Vermaas, is also optimistic that significantly higher fatty acid yields will be obtainable, as research continues.

The research opens the door to practical use of this promising source of clean energy.

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Citation: Microbes reprogrammed to ooze oil for renewable biofuel (w/ Video) (2010, March 29) retrieved 18 July 2019 from https://phys.org/news/2010-03-microbes-reprogrammed-ooze-oil-renewable.html
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Mar 29, 2010
I would think so.

I would like to see some numbers. For instance- what is yield of fatty acids per kg of cyanobacterium per 24 hours? that would be useful information.

Just the same, another stride in the right direction.

Mar 29, 2010
getting the oil from the cell had been quite unattainable until now...this is a big potential step

Mar 29, 2010
Amazing work truly excellent but when will we see a commercial system? Even if yeilds were lowish the knowledge should be transferred to some of the many startup companies already working on practical production as soon as possible to get things happening after all there is lots of profit in transport fuels.

Mar 29, 2010
Inspirational work that could change the geopolitics of the world.

Mar 29, 2010
The yield would be a function of surface area exposed to sunlight, so comparisons to solar farms would be in order.

Mar 29, 2010
Would this allow small "farmers" to get in the production of the "fatty acids" used to make the fuel?

Perhaps allow small, local area "refiners"?

Or, will this just be another Exxon, Mobil, BP oil product line?

Mar 30, 2010
@Bob B.
I'm sure that they would be happy to license the technology to whoever could afford the fees.
Tech transfer to smallholder production might even be eligible for a Fed small business loan, or other program funds, given the push for green tech development currently underway.
Certainly worth checking into, if you are thinking along those lines.

Mar 30, 2010
I hope that when this GMO "escapes", we don't end up with fat slicks on our oceans and waterbodies.

Mar 30, 2010
I was worrying about Holstein's escaping into the wild and mucking up my favorite national park with milk run-off. Now I've got butter on the beach to fret over. How will I ever sleep again? Maybe I'll get over it loving the $1 per gallon of diesel. Yeah, Ill deal.

Mar 30, 2010
Presumably there's some way to keep these little charmers from escaping into the environment and killing off all competing life forms?

Mar 30, 2010
This variant almost certainly would be unable to compete with wild cyanobacteria. For one thing, overproduction of lipids is a waste of energy.

Generally, GMOs are less fit than their wild variants. If that weren't the case, the wild variants would already have incorporated these modifications.

Apr 03, 2010
For maximum efficiency,a closed system would be essential.Open pond production allows wild species to contaminate the GMOs.A system like that developed by Valcent Technologies for algae modified to use these GMOs should do the trick.See:http://video.goog...73275016

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