Researchers engineer E. Coli to produce ethanol directly from brown seaweed with yield equivalent to ~80% of the theoretical maximum
20 January 2012
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| Design of the microbial platform for production of biofuels and renewable commodity chemical compounds from macroalgae. Wargacki et al. Click to enlarge. |
A team of scientists from Bio Architecture Lab (BAL) in Berkeley, California, (earlier post) has engineered a strain of Eschericia coli to break down and then to ferment alginate—one of the most abundant sugars in brown algae, but a sugar that industrial microbes can’t metabolize—into ethanol. Their paper is featured on the cover of the 20 January issue of the journal Science.
When engineered for ethanol synthesis, the BAL microbial platform produced bioethanol directly from macroalgae via a consolidated process (CBP), achieving a titer of 4.7% volume/volume and a yield of 0.281 weight ethanol/weight dry macroalgae (equivalent to ~80% of the maximum theoretical yield from the sugar composition in macroalgae).
Macroalgae (seaweed) offers a number of attractive attributes as a feedstock for renewable fuels and chemicals (high sugar content, no requirements for arable land, fresh water, and fertilizer and no food vs. fuel issues. Furthermore, the team notes in their paper, because brown macroalgae does not contain lignin, sugars can be released by simple operations such as milling or crushing. About 60% of the dry biomass of the seaweed are sugars, with more than half of that being alginate, said Daniel Trunfio, Chief Executive Officer at Bio Architecture Lab.
This bio-architectural feature gives macroalgae a distinct advantage over lignocellulosic biomass, facilitates higher yields, and averts the need for energy-intensive pretreatment and hydrolysis processes before fermentation. An analysis prepared for the US Department of Energy (DOE) reports a macroalgae productivity of 59 dry metric tons/ha/year and an ideal ethanol yield from macroalgae of 0.254 weight (wt) ethanol/wt dry macroalgae. Based on these numbers, an optimum bio-ethanol productivity of 19,000 liters/ha/year is estimated. This value is approximately two times higher than the ethanol productivity from sugarcane and 5 times higher than the ethanol productivity from corn.
The most abundant sugars in brown macroalgae are alginate, mannitol, and glucan (glucose polymers in the form of laminarin or cellulose). Ethanol production from glucan and mannitol yields approximately 0.08 to 0.12 wt ethanol/wt dry macroalgae. However, the full potential of ethanol production from macroalgae cannot currently be realized because of the inability of industrial microbes to metabolize the alginate component.
—Wargacki et al.
The BAL team developed a pathway to metabolize the alginate. Core to the work is the discovery of a DNA fragment from the bacterium Vibrio splendidus encoding enzymes for alginate transport and metabolism. The BAL team integrated this with other elements to generate a microbial platform that can simultaneously degrade, uptake, and metabolize alginate.
In the new platform, the alginate polymer is first degraded into oligomers (short fragments) by an alginate lyase secreted by the cells, the gene for which came from the bacterium Pseudoalteromonas sp. The oligomers are then transported into the E. coli using capabilities endowed by some of the V. splendidus fragment. Other V. splendidus genes contributed to metabolizing the alginate oligomers and allowed them to be converted into chemical building blocks. A pathway from Zymomonas mobilis turns that into ethanol.
BAL earlier was a beneficiary of the US Department of Energy’s Advanced Research Projects Agency - Energy (ARPA-E) awarded to DuPont, for the development of a process to convert sugars from seaweed into isobutanol.
BAL’s technology to ferment a seaweed feedstock to renewable fuels and chemicals has created an entirely new pathway for biofuels development, one that is no longer constrained to terrestrial sources. When fully developed and deployed, large scale seaweed cultivation combined with BAL’s technology promises to produce renewable fuels and chemicals without forcing a tradeoff with conventional food crops such as corn or sugarcane.
—ARPA-E Program Director Dr. Jonathan Burbaum
In addition to work for DuPont, the development of BAL’s technology is also supported by the Concurso Nacional Grant provided by InnovaChile CORFO and Statoil. In 2010, BAL and Statoil formed a strategic partnership for the production of ethanol derived from macroalgae grown off the coast of Norway. (Earlier post.)
Resources
Adam J. Wargacki, Effendi Leonard, Maung Nyan Win, Drew D. Regitsky, Christine Nicole S. Santos, Peter B. Kim, Susan R. Cooper, Ryan M. Raisner, Asael Herman, Alicia B. Sivitz, Arun Lakshmanaswamy, Yuki Kashiyama, David Baker, and Yasuo Yoshikuni (2012) An Engineered Microbial Platform for Direct Biofuel Production from Brown Macroalgae. Science 335 (6066), 308-313. doi: 10.1126/science.1214547
Erik Stokstad (2012) Engineered Superbugs Boost Hopes of Turning Seaweed Into Fuel. Science335 (6066), 273. doi: 10.1126/science.335.6066.273
These lab results sound good, but how/where are you going to build a commercial scale production system to provide the raw materials and produce a product at commercial quantities? I assume a processing/production facility would need to be located as close to a saltwater waterbody as possible. E. Coli is a nasty microbe so there are concerns with using it properly also. Would you ever be able to continually grow enough brown seaweed to keep up with demand at the processing plant / refinery? Sounds more risky and complicated than Range Fuels.
Posted by: ejj | 20 January 2012 at 04:13 AM
ejj:
There are plenty of saline aquifers in the US, and waste from chicken farms and so on can also be used:
http://newenergyandfuel.com/http:/newenergyandfuel/com/2010/12/06/the-biomass-algae-research-target-is-shifting-to-seaweed/
I'm coming out to around 500,000 square kilometres to replace the 20 million barrels of oil the US uses, if my math is right.
This is the right kind of scale, and the resouces used are in the right ball park to make this a genuine large scale fuel source.
Posted by: Davemart | 20 January 2012 at 04:57 AM
Davemart - great link. The graphic makes it's point.
Posted by: kelly | 20 January 2012 at 07:34 AM
I forgot to adjust for the lower energy dnesity of ethanol, which is around 60% of that of diesel.
The figure should be perhaps 800,000sq kilometres, although of course the oil imported has considerable refining losses.
Posted by: Davemart | 20 January 2012 at 07:44 AM
Producing fuels from non-food production areas may be an acceptable and sustainable solution for future production of essential fuels and chemicals. Any idea on the total cost per unit?
Posted by: HarveyD | 20 January 2012 at 08:15 AM
People keep trying to say what is required to replace 20 million barrels of oil per day. Even if this replaces 20% of that, we are ahead of the game. That would allow us to eliminate importing ANY OPEC oil at ALL!
Posted by: SJC | 20 January 2012 at 08:18 AM
Yeah, no one seriously imagines that this would replace all oil use.
I like to run the numbers just to check an idea for size, to see if it is only viable as a niche, can make a major contributiion or can solve all our energy issues on its own.
Previously biofuels were very much a niche, and rather a distraction.
Now clearly this is not going to substitute for all oil, not using 800,000 kilometres land its not, if I got my figures right, but also it can could take care of air and perhaps trucking, so I would class this as potentially a 'major contribution.'
Posted by: Davemart | 20 January 2012 at 08:33 AM
I figure if we can get even half the big rig tractors on LNG/DME we have eliminated middle eastern oil THIS decade. If we want to keep from going to yet another Oil War in the next ten years, that would be a good start.
Posted by: SJC | 20 January 2012 at 10:23 AM
Davemart, I think that biofuels are still “very much a niche, and rather a distraction”.
At a annual yield of 19,000 liters per hectare, the efficiency of conversion from solar energy to thermal energy is less than 1%.
The annual solar radiation in the US heartland is about 1500 kWh per sq. meter, or 15,000,000 kWh per hectare. At 5.87 kWh / liter, 19,000 liters of ethanol has a thermal energy of 111,000 kWh, which is a 0.74% conversion efficiency. Based on comparisons in the article, ethanol from sugar cane and corn would have even lower solar to thermal energy conversion efficiencies of ~ 0.4% and ~0.15%, respectively. As for land usage, .....
Posted by: NorthernPiker | 20 January 2012 at 03:05 PM
PV EV wins in miles per m2
Short range PHEV and PV would be a good match.
Posted by: 3PeaceSweet | 20 January 2012 at 04:16 PM
3PeaceSweet:
As the figures I gave indicate, we are not going to be running the light vehicle fleet on this.
OTOH we are not going to be running heavy trucking or aircraft on batteries, and so we need 'something else' with better energy density.
This could be a helpful 'something else.'
Posted by: Davemart | 21 January 2012 at 01:49 AM
We are going to need liquid fuels for some time to come. Whether we continue to get them from refined oil is the question. The world either has or soon will hit peak oil production and demand will continue to rise. We just need to face those facts and act accordingly.
Posted by: SJC | 22 January 2012 at 11:03 AM