MSU releases third corn variety for cellulosic ethanol
January 1, 1970
BY Jerry W. Kram
Web exclusive posted April 23, 2008 at 12:15 p.m. CST
Michigan State University researchers have introduced their third corn variety tailored for cellulosic ethanol. The varieties – dubbed Spartan 1, 2 and 3 – are genetically modified to express cellulase enzymes in the stalk and leaves. Together, the enzymes from the three varieties convert cellulose into glucose which can be fermented into ethanol.
Spartan 1 was given an endoglucanase which was discovered in a bacteria living in a hot spring, said Mariam Sticklen, professor of crop and soil science at MSU. The endoglucanase breaks long chains of cellulose into shorter fragments. Spartan 2 contains a gene from a soil fungus for an exoglucanase that breaks the fragments into molecules containing two glucose units called dimers. Spartan 3 produces a beta glucanase, also called cellobiase, which cleaves the dimers into two glucose molecules which yeast can ferment into ethanol. The gene for the final enzyme was extracted from a microbe that lives in the rumen, or second stomach, of cattle.
The key to producing Spartan 3 was expressing the gene in a way where the enzyme won't attack the cellulose in the plant while it's still growing. To accomplish this, Sticklen managed to get the corn to express the beta glucanase in vacuoles. "I call the vacuole the garbage can of the cell," she said. "Everything needed in the cell goes into the vacuole so the normal cellular metabolism in the cytoplasm remains intact." The vacuole grows until it takes up 80 percent of the cell's volume by harvest time. The enzyme is only expressed in the leaves and stem of the plant. The grain, pollen and roots of the plant are unaffected, so the enzyme will not enter the environment or food supply. Spartan 1 and 2 store their enzymes in different parts of the cell. When the corn stover is ground and processed, the enzyme is released.
The three varieties of corn will be blended with regular corn stover in a cellulosic ethanol plant. Sticklen said the Spartan corn enzymes will be much less expensive than conventional enzymes produced by bacteria. Testing has shown the proper ratio for the three enzymes is four parts Spartan 2 to one part each of Spartan 1 and Spartan 3. "We have completed our tests which not only shows that our corn can dissolve commercial cellulose but also pretreated corn stover that we borrowed from a chemical engineering laboratory," she said.
Negotiations are in progress with a number of seed companies to license the Spartan varieties. Sticklen said work is continuing on at least two more varieties in the Spartan series of corn. Her work is concentrating on making the plants store the enzymes in multiple locations in the cell to increase the enzyme content in the full grown plant.
Michigan State University researchers have introduced their third corn variety tailored for cellulosic ethanol. The varieties – dubbed Spartan 1, 2 and 3 – are genetically modified to express cellulase enzymes in the stalk and leaves. Together, the enzymes from the three varieties convert cellulose into glucose which can be fermented into ethanol.
Spartan 1 was given an endoglucanase which was discovered in a bacteria living in a hot spring, said Mariam Sticklen, professor of crop and soil science at MSU. The endoglucanase breaks long chains of cellulose into shorter fragments. Spartan 2 contains a gene from a soil fungus for an exoglucanase that breaks the fragments into molecules containing two glucose units called dimers. Spartan 3 produces a beta glucanase, also called cellobiase, which cleaves the dimers into two glucose molecules which yeast can ferment into ethanol. The gene for the final enzyme was extracted from a microbe that lives in the rumen, or second stomach, of cattle.
The key to producing Spartan 3 was expressing the gene in a way where the enzyme won't attack the cellulose in the plant while it's still growing. To accomplish this, Sticklen managed to get the corn to express the beta glucanase in vacuoles. "I call the vacuole the garbage can of the cell," she said. "Everything needed in the cell goes into the vacuole so the normal cellular metabolism in the cytoplasm remains intact." The vacuole grows until it takes up 80 percent of the cell's volume by harvest time. The enzyme is only expressed in the leaves and stem of the plant. The grain, pollen and roots of the plant are unaffected, so the enzyme will not enter the environment or food supply. Spartan 1 and 2 store their enzymes in different parts of the cell. When the corn stover is ground and processed, the enzyme is released.
The three varieties of corn will be blended with regular corn stover in a cellulosic ethanol plant. Sticklen said the Spartan corn enzymes will be much less expensive than conventional enzymes produced by bacteria. Testing has shown the proper ratio for the three enzymes is four parts Spartan 2 to one part each of Spartan 1 and Spartan 3. "We have completed our tests which not only shows that our corn can dissolve commercial cellulose but also pretreated corn stover that we borrowed from a chemical engineering laboratory," she said.
Negotiations are in progress with a number of seed companies to license the Spartan varieties. Sticklen said work is continuing on at least two more varieties in the Spartan series of corn. Her work is concentrating on making the plants store the enzymes in multiple locations in the cell to increase the enzyme content in the full grown plant.
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