Science News - August 11, 2012

even lend a hand in the synthesis of drugs and supplements such as vitamin E.

But enzyme-driven processes these days can get much more involved than just throwing starting materials into an animal gut. Often materials need to undergo additional reactions, treatment with a solvent or dyeing with a chemical, before or after an enzyme can do its job. For many of these reactions, heat is required as a catalyst.

The problem: Most known enzymes
work only at conditions matching those
of the organism from which they came.
So temperatures have to be repeatedly
ramped up and lowered at various stages
of a multistep process. “You have to cool
it down for the biological part and heat
it back up for the next step,” says Vicki
Thompson of Idaho National Labora-
tory in Idaho Falls. “That makes the
process more expensive, and it’s waste-
ful of energy.”
During low-temperature stages, mate-
rials can also be vulnerable to attack
from a plethora of microbes.

The breakdown of long chains of glucose molecules from plants, or cellulose, faces such troubles. Cellulose stored in corn stover — the grassy part of corn that people don’t eat and a potential biofuel source — is tied up in complex chemical arrangements, making it hard for enzymes working alone to get access.

So the biomass has to be mashed up a bit first. It’s heated and treated with corrosive chemicals like acids or salty solutions, which expose the cellulose. But the plant products have to be neutralized and cooled before a collection of room-temperature enzymes can digest the material into usable sugars.

Cellulose-breaking enzymes, called cellulases, made by organisms that normally thrive under extreme conditions, in places like hot springs or hydrothermal vents, could offer a solution.

“You can take those enzymes and use them under the industrial conditions that you are interested in,” explains Thompson, who has been studying organisms that live in extreme environments and the proteins they make for more than a decade.

Biologist Thomas Brock unearthed one of the first known extremophiles from hot pools in Yellowstone National Park in Wyoming in the 1960s. Later named Thermus aquaticus, the bacterium thrived best at temperatures around 70° C. This finding suggested life could exist in all kinds of places that were previously thought of as dead zones.

Explorations in volcanic soil, hot vents, deep seas and salt deserts have turned up thousands of extremophiles since, says Thompson. A sizable portion love the heat. Notably, a heat-loving, DNA-building enzyme from T. aquaticus has been a major boon for genetic engineering and forensics. To analyze DNA from collected samples, scientists need large amounts of uncontaminated copies. By simply adding the enzyme, Taq polymerase, to a starting strand of DNA and other genetic ingredients, scientists can make lots of DNA copies with no contamination to worry about.

Over the last two decades, Frank Robb of the University of Maryland, Baltimore has scoured some of the hottest corners of the Earth — from the hot springs at Yellowstone to the deep-sea vents of the Okinawa Trough — in search of interesting heat-loving enzymes. An ability to break down cellulose is one sought-after skill in the “help wanted” ads.

Robb and Graham want cellulases
that can do their thing at temperatures
of 100° C or even higher. The more
types the better, since some enzymes
specialize in cutting the cellulose into
chunks and some break it down even
further into glucose.

Fueled by heat From a hot pool in Nevada (above), researchers pulled a cellulose-busting enzyme called EBI-244. The enzyme shows its maximum breakdown activity above 100° Celsius (right), making it a good candidate for use in biofuel production.