Fungus Has Future in Plastics Manufacturing

WASHINGTON, April 27, 2000--A new bioengineered fungus could usher in truly biodegradable plastic milk jugs and soda bottles that don’t hang around landfills for ages. This fungus could become a “workhorse” in converting grain and other renewable agricultural resources into environmentally friendly solvents and plastics.

“The research on utilization of agricultural products such as cornstarch and fibrous crop residues bodes well for both farmers and consumers,” said Floyd P. Horn, administrator of USDA's Agricultural Research Service.

ARS has applied for patent protection on an invention that can team microbes with the machinery to produce more lactic acid at less cost. Lactic acid is the building block of polylactic acid (PLA) plastic. The plastic is similar to polyethylene terephthalate or PET used in packaging.

In research at the ARS National Center for Agricultural Utilization Research, Peoria, Ill., microbiologist Christopher D. Skory first isolated an enzyme called lactate dehydrogenase (Ldh) produced by the fungus Rhizopusoryzae. The amount of enzyme produced determines how efficiently the fungus can produce lactic acid. After researching the isolated enzyme, Skory cloned the gene responsible for Ldh synthesis and bioengineered the fungus to have multiple copies of the gene.

“We’ve developed a system that’s helped us improve upon something the fungus already did quite well,” says Skory. “So far, some of our strains are producing about 30 percent more lactic acid in considerably less time than the original strains.” The new strains are being tested for their potential through a Cooperative Research and Development Agreement with industry.

Engineering into the new strains a more efficient route for fermenting sugars meant less energy would be wasted on making unwanted byproducts. “It’s like widening one fork of a stream to increase the flow in that specific direction,” says Skory.

Because the new microbial strains don’t need a lot of added nutrients in their diets of sugars derived from the plant material, the lactic acid they produce during fermentations is easier to purify for making clear plastic. Even before the new improved strains came about, the emerging PLA industry was using R. oryzae, because it produces lactic acid with uniform quality that’s superior to a mix of lactic acids from bacterial fermentations, Skory says.

Lactic acid and its derivatives have many uses other than for plastics. For example, lactic acid is commonly used in foods ranging from soda to sausages because it preserves, enhances flavor or imparts desired acidity. Derivatives of lactic acid such as the solvent ethyl lactate can also be used in manufacturing electronic products, cosmetics textiles, paints, adhesives, de-inkers and degreasers. Environmentally friendly, chlorine-free ethyl lactate some day could supplant most of the present 3.8 million-ton market for petroleum- derived solvents.

Presently, some 5 to 7 percent of petroleum used in the U.S. goes into the manufacture of plastics, according to industry estimates.

ARS is the U.S. Department of Agriculture’s chief scientific research agency.

Scientific contact: Christopher D. Skory, ARS National Center for Agricultural Utilization Research, Peoria, IL 61604; phone (309) 681-6275; fax (309) 681-6567; [email protected].