image title

Solving a sweet problem for renewable biofuels and chemicals

June 30, 2017

ASU scientists harness the trial-and-error power of evolution to coax nature into revealing answer to energy challenge

Whether or not society shakes its addiction to oil and gasoline will depend on a number of profound environmental, geopolitical and societal factors.

But with current oil prices hovering around $50 dollars a barrel, it won’t likely be anytime soon.

Despite several major national research initiatives, no one has been able to come up with the breakthrough renewable biofuel technology that would lead to a cheaper alternative to gasoline. 

That research challenge led ASU scientists Reed Cartwright and Xuan Wang to enter the fray, teaming up to try to break through the innovation bottleneck for the renewable bioproduction of fuels and chemicals.

“My lab has been very interested in converting biomass such as agricultural wastes and even carbon dioxide into useful and renewable bio-based products,” said Wang
(pictured above, right), an assistant professor in the School of Life Sciences. “As a microbiologist, I’m interested in manipulating microbes as biocatalysts to do a better job.”

To do so, they’ve looked into a new approach: harnessing the trial-and-error power of evolution to coax nature into revealing the answer.

By growing bacteria over generations under specially controlled conditions in fermentation tanks, they have test-tube-evolved bacteria to better ferment sugars derived from biomass — a rich, potential renewable-energy source for the production of biofuels and chemicals. Their results appeared recently in the online edition of PNAS.

The research team includes postdoctoral scholar Christian Sievert, Lizbeth Nieves, Larry Panyon, Taylor Loeffler and Chandler Morris, and was led by Cartwright and Wang, in a collaboration between the ASU’s School of Life Sciences and the Biodesign Institute.

A sweet problem

The appeal of plants is ideal. Just add a little carbon dioxide, water and plentiful sunshine, and presto! Society has a rich new source of renewable carbons to use.  

Corn ethanol (using starch from corn for alcohol production primarily in the U.S.) has been one major biofuel avenue, and sugarcane another alternative (abundant in Brazil) — but there is a big drawback. Turning the sugar-rich kernels of corn or sugarcane into ethanol competes with the food supply.

So scientists over the past few decades have migrated to research on conversion of non-food-based plant materials into biofuels and chemicals. These so-called lignocellulosic biomasses, like tall switchgrasses and the inedible parts of corn and sugarcane (stovers, husks, bagasses, etc.) are rich in xylose, a five-carbon, energy-rich sugar relative of glucose.

Lignocellulosic biomass has an abundance of glucose and xylose, but industrial E. coli strains can’t use xylose because when glucose is available, it turns off the use of xylose. And so, to date, it has been an inefficient and costly to fully harvest and convert the xylose to biofuels. 

Benchtop evolution

Wang and Cartwright wanted to squeeze out more energy from xylose sugars. To do so, they challenged E. coli bacteria that could thrive comfortably on glucose — and switch out the growth medium broth to grow solely on xylose.

The bacteria would be forced to adapt to the new food supply or lose the growth competition.

They started with a single colony of bacteria that were genetically identical and ran three separate evolution experiments with xylose. At first, the bacteria grew very slowly. But remarkable, in no more than 150 generations, the bacteria adapted and, eventually, learned to thrive in the xylose broth. 

Next, they isolated the DNA from the bacteria and used next-generation DNA sequencing technology to examine the changes within the bacteria genomes. When they read out the DNA data, they could identify the telltale signs of evolution in action, mutations.

Nature finds a way

The bacteria, when challenged, randomly mutated their DNA until it could adapt to the new conditions. They held on to the fittest mutations over generations until they became fixed beneficial mutations.

And in each case, when challenged with xylose, the bacteria could grow well. Their next task was to find out what these beneficial mutations were and how did they work. To grow better on xylose, the three bacterial E. coli lines had “discovered” a different set of mutations to the same genes. The single mutations the research team identified all could enhance xylose fermentation by changing bacterial sugar metabolism.

“This suggests that there are potentially multiple evolutionary solutions for the same problem, and a bacterium’s genetic background may predetermine its evolutionary trajectories,” said Cartwright, a researcher at ASU’s Biodesign Institute and assistant professor in the School of Life Sciences.  

The most interesting mutation happened in a regulatory protein called XylR whose normal function is to control xylose utilization. Just two amino acid switches in the XylR could enhance xylose utilization and release the glucose repression, even in the non-mutated original hosts.

Through some clever genetic tricks, when the XlyR mutant was placed back in a normal “wild-type” strain or an industrial E. coli biocatalyst, it could also now grow on xylose and glucose, vastly improving the yield. Wang’s team saw up to a 50 percent increase in the product after four days of fermentation. 

Together, Wang and Cartwright’s invention has now significantly boosted the potential of industrial E. coli to be used for biofuel production from lignocellulosic materials. In addition, they could use this same genetic approach for other E. coli strains for different products.

Arizona Technology Enterprises (AzTE) is filing a non-provisional patent for their discovery. Wang hopes they can partner with industry to scale up their technology and see if this invention will increase economic viability for bioproduction.  

“With these new results, I believe we’ve solved one big, persistent bottleneck in this field,” Wang said. 

 

Top photo: ASU undergraduate Eric Taylor (left) and Xuan Wang demonstrate the fermentation tanks used in the benchtop evolution experiments.​

Joe Caspermeyer

Managing editor , Biodesign Institute

480-258-8972

 
image title
AZLoop team on schedule to show working prototype at SpaceX competition.
June 30, 2017

ASU-led team to begin testing propulsion and braking systems the first week of July as SpaceX competition approaches

The lazy days of summer are anything but for the AZLoop team.

With the Aug. 27 SpaceX competition fast approaching, the team has been busy building propulsion and braking systems, as well as the form needed to mold the pod that will run during the August event.

The goal: creating a working prototype of a new form of proposed mass transit called “Hyperloop” that promises to hit speeds of up to 750 mph.

The team — led by Arizona State University but made up of students from throughout Arizona in a range of majors — is on track to complete the project on time. A 50-foot test track has been built at the ASU Polytechnic campus; they’ll begin testing magnetic propulsion and braking systems the first week of July. Construction of a 150-foot track will begin in early July, with a completion date of around Aug. 1.

Video by Ken Fagan/ASU Now

According to Josh Kosar, co-lead on the project and a new ASU graduate, they started out with a well-defined organizational structure but over time have had to make lots of changes to adapt to individual work styles and skill sets. New leaders emerged, adjustments were made and now the process is working out well.

“The most important thing I have learned so far as manufacturing lead is to manage a team,” said ASU mechanical engineering junior Himanshu Dave. “… Knowing their strengths and weaknesses as well as your own and understanding that has been one of the best skills I have learned.”

A precision-cut scale model of the pod is being produced in layers that will be attached to each other to shape the final pod design. The team will cover it with Bondo to fill in around the rough edges of the wood layers before it is sanded and primed. 

“It’s all experimentation, lifting up the shape of it, changing it a little bit,” Dave said.

Magnetic braking systems are in the works, as well as propulsion systems. They will be attached to a sled filling in as the pod to test forward motion and braking systems on the 50-foot track.

“They’ve got what it takes. They are careful and rational,” said ASU Professor John Robertson, lead faculty adviser. “It’s like in any race — you want to blow through the finish line, you don’t want to fall over the finish line. You’ve got to blow through it, and I think that is what they are going to do.” 

Top photo: ASU mechanical engineering junior Himanshu Dave (left) gets some guidance from Chandler Gilbert Community College student Ernest Poteat on how to treat the layered model for the vehicle's carbon fiber shell on ASU's Polytechnic campus on Thursday, June 29. The mechanical team will cover the model with Bondo Body Filler, sand it smooth, paint on primer then a release agent and follow that with the carbon fiber strips. When completed in about six weeks, it will be attached to the vehicle the AZLoop team will take to the August SpaceX Hyperloop Pod Competition in California. Photo by Charlie Leight/ASU Now

Ken Fagan

Videographer , ASU Now

480-727-2080