INEEL uses extremophile bacteria to ease bleaching's environmental cost

10/13/04

In the steamy waters of Yellowstone National Park's hot springs lives a type of bacterium that could help make industrial bleaching cheaper and more environmentally friendly. Scientists have found Thermus brockianus bacteria produce a hardy enzyme that can be put to work breaking down hydrogen peroxide in industrial wastewater, producing only harmless oxygen and water as byproducts. Most important, the so-called extremozyme endures harsh industrial conditions better than currently available alternatives and lasts thousands of times longer.

R&D Magazine declared the isolation and production of the enzyme -- named the Ultrastable Catalase Enzyme by the Department of Energy's Idaho National Engineering and Environmental Laboratory researchers who found it -- to be one of the 100 most significant technological achievements of 2004. Chemical engineer Vicki Thompson and biologists William Apel and Kastli Schaller from INEEL will be recognized at the R&D Magazine awards banquet in Chicago on Oct. 14, 2004.

"It's exciting that the R&D 100 chose a project involving extremophiles," Thompson says. "It will help spread the word about the practical applications and environmental benefits that can come from extremophilic research."

Since the 1980s, cloth and paper manufacturers and other industries have experimented with using hydrogen peroxide instead of toxic chlorine bleach to whiten and disinfect products. Hydrogen peroxide can rid fresh fruits and vegetables of harmful bacteria such as Salmonella and E. coli; pasteurize dairy products; and sterilize paper food packages such as juice boxes, which eliminates the need for refrigeration.

To remove the hydrogen peroxide left over in wastewater after bleaching, some industrial chemists turn to a special type of enzyme called a catalase. Catalase enzymes, found in most living things, break down hydrogen peroxide into water and oxygen. This protects cells from oxidative stress -- the biological equivalent of rust.

But industrial waters can push enzymes to their limit. Most commercial catalase enzymes hail from organisms that prefer moderate temperatures, such as cows and fungi; high temperatures and high pH of industrial processes destroy these enzymes quickly.

"Animals and people are designed to operate between 95 and 105 degrees Fahrenheit," Thompson says. "Any catalase derived from a mammal is not going to be stable at extreme conditions."

The INEEL team isolated the catalase enzyme from T. brockianus and found its industrial half-life to be 15 days instead of the 15 seconds of other catalase enzymes -- an 86,000-fold improvement. Scientists use an enzyme's half-life -- the amount of time it takes to lose half its effectiveness -- as a yardstick for comparing two enzymes.

Large-scale production of the T. brockianus enzyme could end decades of environmental costs from industrial bleaching. Chlorine, used for more than a century, forms toxic and carcinogenic chemicals called dioxins as byproducts. Industries switching to greener hydrogen peroxide have developed wastewater treatment options -- though all have come with extra cost or environmental problems.

One hydrogen peroxide treatment dilutes wastewater with pure water, but this drives up cost and produces even more waste. Another solution treats wastewater chemically with salts, but its harmful residue essentially cancels out the environmental benefits of using hydrogen peroxide in the first place.

The most direct wastewater treatment uses a catalase to break down hydrogen peroxide. But scientists working with commercial catalases have had to make a choice: either spend time and money bringing wastewater temperatures and pH down to tolerable levels, or else continually add more catalase to untreated wastewater to replenish the enzyme.

With the T. brockianus extremozyme, hydrogen peroxide decomposes safely, and wastewater needs no extra pretreatment. What's more, the enzyme lasts long enough to treat multiple batches of wastewater.

Thompson didn't set out to find an enzyme specifically for bleaching applications, she says. The INEEL team stumbled on T. brockianus in 160-degree Yellowstone pools as part of its extremophile research, studying organisms named for their love of extreme living conditions that would snuff out most living creatures.

But when she examined the bacteria, Thompson quickly recognized its potential. "We purified the enzyme, and it was robust, hardy, and stable," she says. In fact, the T. brockianus enzyme has been the only catalase to boast such industrial-strength properties.

Potential applications came next, Thompson recalls. "It was so stable that we said, 'There's got to be a place this can be used,' and we started looking around. We found the answer in industrial bleaching."

Still puzzling to Thompson, however, is why the extremozyme survives alkaline waters better than its mammalian counterparts do. Its long life in high-temperature wastewater can be traced back to T. brockianus' fondness for hot springs. But it turns out the bacterium doesn't fare as well as its enzyme in high pH conditions.

"Along the way, we may figure out why the enzyme is stable in alkaline environments," Thompson says. "But if it works in industry, that's the most important thing right now."

The INEEL team is discussing collaborations for industrial development with major enzyme manufacturers. After isolating and producing large quantities of the enzyme in the lab, scientists can use existing technology to chemically bind them to tiny plastic beads the size of sand grains. Columns packed with the plastic-and-enzyme beads can filter wastewater and break down hydrogen peroxide, Thompson says. And since the enzyme retains its stability, the beads can be reused to treat additional batches of wastewater.

The INEEL is a science-based, multiprogram national laboratory dedicated to advancing the U.S. Department of Energy's strategic goals in the areas of environment, energy, science and national security. It is the home of science and engineering solutions and is operated for the DOE by Bechtel BWXT Idaho, LLC.

Source: Eurekalert & others

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