Engineered enzymes could make gas cheaper

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Researchers have shown how to design and genetically engineer enzyme surfaces so they bind less to corn stalks and other cellulosic biomass, reducing enzyme costs in the production of biofuels like the ethanol in US gasoline.

“The bottom line is we can cut down the cost of converting biomass into biofuels,” says Shishir P. S. Chundawat, senior author of the study and an assistant professor in the chemical and biochemical engineering department at Rutgers University-New Brunswick.

“…any advances on making the enzyme processing step cheaper will make the cost of biofuel cheaper.”

Typically, the enzymes tapped to help turn switchgrass, corn stover (corn stalks, leaves, and other leftovers), and poplar into biofuels amount to about 20 percent of production costs, says Chundawat. Enzymes cost about 50 cents per gallon of ethanol, so recycling or using fewer enzymes would make biofuels more inexpensive.

In the United States, gasoline typically contains up to 10 percent ethanol and corn grain is the primary feedstock of ethanol, according to the US Energy Information Administration. Biorefineries produce about 15 billion gallons of ethanol a year.

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In the last few years, some refineries began converting the inedible parts of corn plants into ethanol, Chundawat says.

“The challenge is breaking down cellulose (plant) material, using enzymes, into sugars that can be fermented into ethanol,” he says. “So any advances on making the enzyme processing step cheaper will make the cost of biofuel cheaper. This is a fairly intractable problem that requires you to attack it from various perspectives, so it does take time.”

Biomass contains lignin, an organic polymer that binds to and strengthens plant fibers. But lignin inactivates enzymes that bind to it, hampering efforts to reduce enzyme use and costs, according to Chundawat.

The researchers showed how specially designed enzymes (proteins) can limit their binding to and inactivation by lignin. That would ultimately lower enzyme use and make enzyme recycling feasible for biorefineries in the near future, Chundawat says.

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The study appears in the journal ACS Sustainable Chemistry & Engineering.

The National Science Foundation supports Chundawat’s ongoing research.

Source: Rutgers University