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Microbe could make biofuels hot

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A 94°C geothermal pool, with a level-maintaining siphon, near Gerlach, Nevada. Sediment from the floor of this pool was enriched on pulverized miscanthus at 90°C and subsequently transferred to filter paper in order to isolate microbes able to subsist on cellulose alone.

A record-breaking microbe that thrives while munching plant material at near boiling temperatures has been discovered in a Nevada hot spring, researchers announced in a study published today.

Scientists are eyeing the microbe’s enzyme responsible for breaking down cellulose — called a cellulase — as a potential workhouse in the production of biofuels and other industrial processes.

Cellulose is a chain of linked sugar molecules that makes up the woody fiber of plants. To produce biofuels, enzymes are required to breakdown cellulose into its constituent sugars so that yeasts can then ferment them into the type of alcohol that makes cars (not people) go vroom.

At the industrial scale, this process is done most efficiently at high temperatures that kill other microbes that could otherwise contaminate the reaction, Douglas Clark, a chemical and biomolecular engineer at the University of California at Berkeley, told me today.

“So finding cellulases that can operate at those temperatures are of interest,” he said.

Hot spring
That’s what led Clark, microbiologist Frank Robb from the University of Maryland, and colleagues to collect sediment and water samples from the Great Boiling Springs near Gerlach, Nevada. The spring is 203 degrees F, just short of boiling.

“It’s on private land and has been surrounded by a low wall to keep cattle from going into it and that maintains the temperature,” Robb explained to me today, noting that most hot springs have varying temperatures depending on the weather and water levels in the spring.

In addition, a siphon has been added to Gerlach hot spring to keep it from overflowing. The combination gives whatever microbes that are in there no choice but to grow at high temperatures, Robb noted. Bits of grass and woody material blown into the spring serve as a food source.

The team grew microbes found in the samples on pulverized miscanthus, a type of grass that is a common biofuel feedstock, to isolate the microbes that grow with plant fiber as their only source of carbon.

They then sequenced the community of surviving microbes, which indicated three species of Archaea, a type of single celled microorganism, were able to utilize cellulose as food. Genetic techniques identified the specific cellulase involved in the breakdown of cellulose.

This cellulase, dubbed EBI-244, was found in the most abundant of the three Archaea.

“We didn’t really expect to find an organism that could grow at such a high temperature and degrade cellulose in this particular environment. But you never know,” Clark told me. “It really underscores the diversity of life. And, obviously, if you don’t look, you won’t find it.”

Too hot
The enzyme EBI-244 works optimally at 228 degrees F (109 degrees C), which is actually too hot for the efficient breakdown of cellulose into fermentable sugars due to side reactions that can occur, Clark noted.

“But it is interesting to know that such cellulases are out there,” Clark said. “And then this cellulase might also serve as a good starting point to be engineered to work at a lower temperature but maintain the high stability that it has naturally evolved to work at such high temperatures.”

Robb likened this engineering process to building a street car from parts used on cars found at the racetrack. “The enzyme itself could be the parts bin,” he said.

So, the enzyme itself probably won’t be hard at work anytime soon producing fuel to put in your gas tank, but it does lead researchers down the road to engineering the biofuels of the future. What’s more, EBI-244 is a record holder for heat tolerance in cellulase.

“It is always nice to have a record breaker,” Clark noted. “It adds to that wow factor a little bit.”

 

Via MSNBC

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