April 27, 2000 / USDA - ARS News Service
WASHINGTON -- 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 Rhizopus
oryzae. 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.
(posted without permission)
