X-fuels and X-bugs

Bio-adjacent, low-carbon extreme fuels and extremophile organisms open up new horizons in yields and sustainability

There are a class of fuels that are deeply rooted in biological process, and share the goal of replacing fossil fuels with low-carbon substitutes, but are not strictly biofuels.

Huh? Well, think of fuels that are generated directly from biomass precursors, such as CO2, water, and sunlight.

Some use micro-organisms to perform the transformation, some are thermo-chemical in nature – but they are making organic molecules, even if they are not making or using life forms that contain DNA.

They are distinct from, say, synthetic fuels made from fossil-based sources, such as coal-to-liquid fuels, because they are low-carbon in nature, even if they are not made from biomass.

There are also a group of new processes bubbling up from the labs – based in extremophile micro-organisms, or new understanding of the role played by symbionts (co-operative “hosted” organisms, such as the bacteria that assist organisms in digestion).

What can we call all these extreme organisms and hard-to-categorize processes? Here at the Digest, we are broadly categorizing them as X-fuels and X-bugs.

The X-fuels – advanced, low-carbon, but not quite bio

Making a low-carbon, renewable fuel, but not using biomass? That’s an X-fuel. All X-fuels are low-carbon, alternative fuels, but not all are, in the strictest sense, biofuels.

Making an alternative fuel, even a biofuel, using the new class of extremophiles and their symbionts? Those are the X-bugs.

Joule Unlimited’s magic cyanobacteria doesn’t process biomass at all – nor do the fuels we reported on yesterday from Air Fuel Synthesis. They are distinct from each other, as well. Joule Unlimited’s process is rooted in synthetic biology – a highly engineered cyanobacteria is at the core of the process. By contrast, Air Fuel Synthesis has a thermochemical process based in CO2 capture, electrolysis and the processing of syngas into fuels.

Now, Joule styles its output as a “solar fuel,” and that’s fine, if not quite capturing the importance of CO2 and water in their process. All solar fuels are X-fuels, but not all X-fuels are solar fuels.

X-bugs – extreme thermophiles

This week, the newest X-bugs are in the news as well. The highlight? Biologists at Berkeley and the University of Maryland discovered a microbe in a Nevada hot spring that has an enzyme that processes cellulose and remains active at a record 109 degrees Celsius (228 degrees Fahrenheit), significantly above the 100℃ (212℉) boiling point of water.

The microbe, a member of the Archaea – a kingdom of organisms distinct from bacteria and prokaryotes (the latter including algae, yeast, fungi, plants, and humans too), was discovered in a 95℃ (203℉) geothermal pool, is only the second member of the ancient Archaea known to grow by digesting cellulose above 80℃. And the microbe’s cellulase is the most heat tolerant enzyme found in any cellulose-digesting microbe.

The group, interestingly, found their magic microbe, in their first sample, in a broad-ranging survey aimed at identifying high-temperature, highly alkaline or acidic, or high salt environments that can provide productive cellulases.

Why are high-temperature bugs preferable – for one, high-temp microbes and proteins can function in an environment that competing or contaminating bugs can’t survive in. Plus, distillation and pre-treatment require high temperatures in most cases – so high-temperature bugs can eliminate the need to heat biuomass for pre-treatment, cool for bioprocessing, and re-heat for distillation – lower energy, lower cost.

The new research is being reported in Nature Communications, authors including Douglas S. Clark, UC Berkeley; Frank T. Robb, University of Maryland; UC Berkeley professor Harvey W. Blanch; postdoctoral researcher Melinda E. Clark, U-Md postdoctoral researcher Joel E. Graham; plus Dana C. Nadler, Sarah Huffer, and Harshal A. Chokhawala of UC Berkeley; and Sara E. Rowland of the University of Maryland Marine, Estuarine and Environmental Sciences graduate program. Research was supported by a grant from the Energy Biosciences Institute (EBI), a public-private collaboration that includes UC Berkeley.

Termites and their magic friends

Over at Purdue, research into the extreme environments in the termite gut, including termite’s own native enzymes, and symbiontic bacteria, is the subject of some breakthroughs out of the Mike Scharf lab. Researchers there, publishing in PLoS One, have discovered a cocktail of enzymes instrumental in the insects’ ability to break down the wood they eat.

The researchers are the first to measure the sugar output from enzymes created by the termites themselves and the output from symbionts, small protozoa that live in termite guts and aid in digestion of woody material.

“For the most part, people have overlooked the host termite as a source of enzymes that could be used in the production of biofuels. For a long time it was thought that the symbionts were solely responsible for digestion,” Scharf said. “Certainly the symbionts do a lot, but what we’ve shown is that the host produces enzymes that work in synergy with the enzymes produced by those symbionts. When you combine the functions of the host enzymes with the symbionts, it’s like one plus one equals four.”

Once the enzymes were identified, Scharf and his team worked with Chesapeake Perl, a protein production company in Maryland, to create synthetic versions. The genes responsible for creating the enzymes were inserted into a virus and fed to caterpillars, which then produce large amounts of the enzymes. Tests showed that the synthetic versions of the host termite enzymes also were very effective at releasing sugar from the biomass.

They found that the three synthetic enzymes function on different parts of the biomass.

Two enzymes are responsible for the release of glucose and pentose, two different sugars. The other enzyme breaks down lignin, the rigid compound that makes up plant cell walls.

What does it all mean?

X-fuels and X-bugs are the cutting edge in alternative fuels these days. While the bio-based magic bugs such as Amyris’s magic yeast, LS9’s magic e.coli, and Solayzyme’s magic microalgae, are readying rapidly for commercial scale, the new class of X-bugs are coming up behind them, with the promise of moving beyond traditional concepts of processing biomass into fuels.

Whether it is processing in extremophile conditions such as high-salt, high-temperature, or highly-acidic environments – moving beyond traditional conditions has the promise to reduce costs, or open up new sources of biomass.

Then there is the new class of X-fuels – moving beyond biomass itself – though it is important to see technologies such as Joule’s not as simply as a magic cyanobacteria that happens to work without biomass. Rather, X-fuels are based in a complete solutions for converting sunlight, CO2 and brackish water into hydrocarbon fuels, rooted in engineering as much as synthetic biology. In Joule’s case, one that happens to have a magic cyanobacteria as one of its critical component parts.

X-fuels and X-bugs – well worth looking forward to as the next wave of low-carbon fuels, chemicals, and materials.