Buried deep in European seas lies a class of microorganisms known as “extremophiles,” so named because of the extreme environmental conditions in which they live. Livermore, Calif.-based Sandia researchers are working on a project aimed at demonstrating various computational tools and enzyme engineering methods that will determine whether the enzymes from these microorganisms could be essential to a new transportation economy based on a renewable biofuel, called lignocellulosic ethanol.
Blake Simmons, a chemical engineering and project lead at Sandia, says the primary hurdle preventing lignocellulosic ethanol from becoming a viable transportation fuel is the efficient and cost-effective processing of lignocellulosic biomass.
“More than a billion tons of biomass are estimated to be created each year in the timber and agricultural industries, as well as a variety of grasses and potential energy crops,” says Simmons. “Unfortunately, you can’t take a tree trunk, stick it into an enzymatic reactor and ferment the sugar produced into ethanol with any kind of efficiency.”
Simmons says the process typically begins by chopping the biomass to reduce its size and then delivering it into a dilute acid pretreatment reactor. The reactor breaks down the biomass into cellulose, hemicellulose and lignin. The polymers released from the biomass must go through additional processing and acid neutralization before the final product is recovered and placed back into an enzymatic reactor to deconstruct the polymers into fermentable sugars. The process is laborious and costly.
However, enzymes isolated from extremophiles are known to exist in organisms that prosper in sulfuric acid environments and, through an inexplicable quirk of nature, efficiently break down cellulose into sugars.
While other researchers are examining common biomass sources and attempting to express enzymes at higher temperatures and lowered pH, Sandia has taken the opposite approach.
“Instead of trying to create an extremozyme from sources that live in benign environmental conditions, why not just manipulate a real one isolated from its natural state?” asks Simmons. Sandia, he says, took the DNA that produces these enzymes into the laboratory, where researchers employ a technique called “site-directed mutagenesis” to manipulate and optimize the enzyme’s genetic sequence in hopes of improving performance. These mutations are identified using computational modeling techniques at Sandia that compare the structure and sequence of extremozymes with their more benign counterparts to identify key genetic sequences of interest.
“The ultimate dream -- and it’s only a dream now -- would be to take a poplar tree, put it into a tank and let it sit for three days, then come back and watch as the ethanol comes pouring out of the spigot,” says Simmons. Though we are decades away from that, this project aims to consolidate the pretreatment steps and get us one step closer to realizing that vision.”