Turn Up the Heat

Researchers explore heat-resistant enzymes
By Kris Bevill | November 15, 2011

Researchers representing the U.S. DOE Joint Genome Institute, Novozymes A/S and Concordia University in Montreal, recently concluded a genome sequencing project for two heat-resistant fungi that is expected to provide solid base information for future biofuels-related enzyme research. Thielavia terrestris and Myceliophthora thermophila had each already been known to thrive in environments with temperatures above 113 degrees Fahrenheit. Researchers had also previously documented the fact that enzymes in those fungi remained active at temperatures ranging up to 167 F, but little else was known about cellulase enzymes produced by the fungi, says Randy Berka, a director at Novozymes in Davis, Calif.

“Thermophilic fungi can be found worldwide, most commonly in habitats where self-heating of plant material results in high temperatures, such as compost heaps, municipal waste, plant straw, and animal dung,” he says. The two species selected for this project were chosen because of their ability to produce enzymes that degrade cellulosic materials at higher temperatures than enzyme blends from nonthermophilic fungi. Samples of the strains used for this project were obtained from culture collections that were originally isolated from soil, Berka says.

The benefits of using enzymes from thermophilic fungi to produce ethanol and other biofuels as well as biochemicals are economical. Enzymes become more active at higher temperatures, so having the ability to turn up the temperature of the production process will mean faster production times and more volume. “The major interest in these enzymes lies in their application for the biochemical/enzymatic route to cellulosic biofuels,” Berka says. “Because the rates of enzyme reactions increase with temperature—sometimes doubling with an increase of just 10 degrees Celsius—a way to reduce the production costs of ethanol from lignocelluloses is to carry out the enzymatic hydrolysis at higher temperatures. This could potentially reduce the reaction time, the retention time in a reactor and the required enzyme loading.”

Researchers also tested the enzymes’ effectiveness at breaking down flowering plants under a variety of temperatures and found that the enzymes from those two species of fungi performed well in a variety of temperatures. “Since these thermophiles are much more efficient than other cellulose degraders in breaking down cellulosic biomass, their enzymes are likely to be more active than known cellulases and/or they have developed new strategies for biomass degradation,” says Adrian Tsang, biology professor and director of the Center for Structural and Functional Genomics at Concordia University.

“These thermophilic fungi represent excellent hosts for biorefineries where biomass is converted to biofuels as an alternative to modern oil refineries,” says Igor Grigoriev, leader of the DOE JGI’s Fungal Genomics Program. “The fact that these organisms not only deliver a broad spectrum of heat-tolerant enzymes but can also host new enzymes and be optimized for industrial processes holds great promise for significant improvements over existing systems.”

Following the genome sequencing, researchers now must produce and test the enzymes in pilot-scale conditions to simulate industrial applications. Berka says it’s hard to estimate when the results of this research may be visible in the marketplace, but adds that the findings can be used to advise future enzyme selections and has the potential to decrease the discovery cycle for enzymes from these fungi by up to one year. 

—Kris Bevill