Table of Contents
New Future for Seaweed?
by Steve Nadis, for MIT Sea Grant
uses an inverted microscope to assess the various stages of
Photo: Steve Nadis
As a boy who enjoyed summer vacations on Cape
Cod, Donald Cheney was always intrigued by seaweed, fascinated in
particular by the supple way it moves. "On the beach, seaweed
can seem like a mess," says Cheney, a marine biologist at Northeastern
University's Seaweed Biotechnology Laboratory in Nahant, Mass. "But
when observed in the water, its natural habitat, seaweed has a marvelous
flexibility." Cheney studied marine algae-of which seaweeds
constitute a multicellular form-both in college and graduate
school, and he's worked with seaweeds his entire professional career.
His lab has focused exclusively on red seaweeds, which he considers
the "prettiest" and most commercially valuable.
One plant he's devoted considerable attention
to is Porphyra, or norian edible red seaweed harvested in
aquaculture farms in Japan, primarily for sushi, as part of a $1
billion per year industry. A large market for nori, a nutritive
food source rich in protein and vitamins, also exists in China.
Cheney believes a sizeable seaweed aquaculture industry could be
established in the northeastern United States as well.
In 1991, Coastal Plantations International (CPI),
a Portland, Maine-based company since renamed Phycogen, began efforts
to farm nori in Cobscook Bay of northern Maine using a non-indigenous
species, Porphyra yezoensis, native to Japan. With support from
MIT Sea Grant, Maine/New Hampshire Sea Grant and the National Coastal
Research Institute, Cheney and his colleagues ran a biomonitoring
program from 1996 to 1999 to see whether this exotic species posed
a threat to the local ecosystem. The group set up nets downstream
of the 10 square-kilometer seaweed farm and along the shore to see
what kind of seaweed might attach and grow. As it is next to impossible
to identify Porphyra species just by looking at the plant blades,
the researchers used molecular genetic techniques to show that the
foreign species, P. yezoensis, did in fact grow outside the cultivated
area during the summer. But the plant could not survive the long,
cold winters, meaning that a colony would not take root and replace
Although P. yezoensis did not pose a danger
to the ecology of Cobscook Bay, CPI's efforts to harvest the plant
faltered because of differences in growing conditions between northern
Maine and Japan. The crop did well in the first year, which was
cloudy and wet, but fared poorly in subsequent years because of
too much sunlight. The company asked Cheney whether he could develop
a strain that would grow better in Maine's climate, while still
dying out in the winter to prevent a bioinvasion hazard.
Again aided by MIT Sea Grant and Maine/New Hampshire
Sea Grant, the Northeastern team took up the challenge to produce
a strain with enhanced growth characteristics. Employing a technique
called protoplast fusion, Cheney and his crew succeeded in combining
cells of P. yezoensis with a local Porphyra species, P. umbilicalis.
To do this, they immersed the cells in an enzyme for about two hours
to dissolve the cell walls. Next they added polyethylene glycol,
a chemical related to antifreeze, to the solution. The chemical
binds to water, removing water molecules that separate the inner
cells or protoplasts. If enough chemical is added, the protoplasts
press close together. Then, if the right amount of water is thrown
into the mix, the protoplasts expand, pushing together and "fusing."
Unfortunately, this hydrid did not thrive. But
when the researchers fused two P. yezoensis cells from different
stages of the seaweed life cycle-one in the leaf phase, the
other in the so-called filament stage-the resulting hybrid
grew faster than the original. "Now we need to find another company
interested in farming this strain," Cheney says.
The experience has convinced him that genetic
modification is vital to the success of a seaweed aquaculture industry
in the U.S. Expansion of seaweed cultivation, he says, will mainly
come from improvements to the culture species themselves, rather
than from improvements in culture methods."
Protoplast fusion, he adds, is not genetic engineering,
since the DNA of nori cells was not changed by adding a foreign
gene. The same fusion process could potentially occur in nature,
he says. "We're just increasing the odds."
The next logical step, as Cheney sees it, is
to use genetic engineering to make seaweed more valuable than it
is today. Genes have already been added to rice and tomatoes to
make them produce more beta-carotene, a precursor to vitamin A.
A similar manipulation could be done to nori as well, Cheney says.
His group has already achieved the first genetic transformation
of seaweed yet reported.
Nori enriched with beta-carotene could help
prevent the 500,000 cases of blindness caused in developing countries
each year by vitamin A deficiencies. With other genetic manipulations,
the seaweed might be used to produce drugs, vaccines, and nutritional
supplements for humans or farm animals, says Cheney. "We think nori
has a lot bigger future than just being eaten in sushi."