Mushrooms might serve as biofactories for the production of various
beneficial human drugs, according to plant pathologists who have
inserted new genes into mushrooms.
"There has always been a recognized potential of the mushroom as being a
choice platform for the mass production of commercially valuable
proteins," said Charles Peter Romaine, who holds the John B. Swayne
Chair in spawn science and professor of plant pathology at Penn State.
"Mushrooms could make the ideal vehicle for the manufacture of
biopharmaceuticals to treat a broad array of human illnesses. But nobody
has been able to come up with a feasible way of doing that."

Dr. Romaine and his colleague, Xi Chen, then a post-doctoral scholar at
Penn State and now a Syngenta Biotechnology Inc. research scientist,
have developed a technique to genetically modify Agaricus bisporus - the
button variety of mushroom, which is the predominant edible species
worldwide. One application of their technology is the use of transgenic
mushrooms as factories for producing therapeutic proteins, such as
vaccines, monoclonal antibodies, and hormones like insulin, or
commercial enzymes, such as cellulase for biofuels.

"Right now medical treatment exists for about 500 diseases and genetic
disorders, but thanks to the human genome project, before long, new
drugs will be available for thousands of other diseases," Dr. Romaine
said. "We need a new way of mass-producing protein-based drugs, which is
economical, safe, and fast. We believe mushrooms are going to be the
platform of the future."

To create transgenic mushrooms, researchers attached a gene that confers
resistance to hygromycin, an antibiotic, to circular pieces of bacterial
DNA called plasmids, which have the ability to multiply within a
bacterium known as Agrobacterium.

The hygromycin resistance gene is a marker gene to help sort out the
transgenic mushroom cells from the non-transgenic cells, Dr. Romaine
explained. "What we are doing is taking a gene, as for example a drug
gene, that is not part of the mushroom, and camouflaging it with
regulatory elements from a mushroom gene. We then patch these genetic
elements in the plasmid and insert it back into the bacterium," he
added.

The researchers then snipped small pieces off the mushroom's gill tissue
and added it to a flask containing the altered bacterium.

Over the course of several days, as the bacterium goes through its
lifecycle, it transfers a portion of its plasmid out of its cell right
into the mushroom cell, and integrates the introduced gene into the
chromosome of the mushroom.

Next, the researchers exposed the mushroom cells to hygromycin. The
antibiotic kills all the normal cells, separating out those that have
been genetically altered for resistance.

The test demonstrates that if a second gene, insulin for example, were
to be patched in the plasmid, that gene would be expressed as well.

"There is a high probability that if the mushroom cell has the
hygromycin resistance gene, it will also have the partner gene," Dr.
Romaine added.

The degree of gene expression ultimately depends on where exactly the
imported gene lands in the mushroom chromosome, among a complexity of
other factors, but researchers point out that the process of producing
biopharmaceuticals is potentially faster and cheaper with mushrooms than
conventional technologies. Unlike plants that have long growth cycles,
"with mushrooms, we can use commercial technology to convert the
vegetative tissue from mushroom strains stored in the freezer into
vegetative seed. A crop from which drugs may be extracted could be ready
in weeks," Dr. Romaine said. A mushroom-based biofactory also would not
require expensive infrastructure set up by major drug companies, he
added.

[www.eurekalert.org]