Sweeping the Seas
Marine biologists look
for new ways to solve old problems of ocean pollution.
by Judy Purdy
In the not-too-distant future, scientists
may wield bacterial brooms to sweep the seas free of pollutants.
Genetically engineered microorganisms, or GEMs for short, possess abundant
potential to ameliorate man-made mayhem in marine environments. In the wake
of accidents or oil spills, GEMs could gobble up chemicals that pollute the
ocean, endanger commercial fishing and foul beaches.
But these mighty microbes also may muddy the water they were supposed to clean
There is, for instance, the nagging question of what happens to these bacteria
once their job is done. Will they disappear -- vanish into thin aqua, so to
speak -- without a trace? Or might they subtly disrupt the natural order of
marine life, silently wreaking havoc with populations of native ocean bacteria?
So far, no one knows. But Bob Hodson is determined to find out.
In his lab at the University of Georgia School of Marine Sciences, Hodson has
set up miniature marine microcosms -- complete with salt marsh sediments and
tides that wash in and out -- to study what happens to genetically altered
microorganisms released into marine environments.
"There has been speculation all the way from the crazy doomsday predictions
on the part of environmentalists to the [no-harm-done predictions of] the industrial
sector about their effects on marine ecosystems," Hodson said. "Industry
says, 'These are natural organisms; we have just changed them a little bit, and,
therefore, they are perfectly safe.' The truth probably lies somewhere in the
Studies like the ones Hodson and his colleagues are conducting will help scientists
predict the best ways to manage modified organisms once they are released into
natural environments. Funded by grants from the National Science Foundation,
the National Oceanic and Atmospheric Administration and the Office of Naval
Research, their research will help guide policy makers who will have to grapple
with the regulation of GEMs.
There's a lot more at stake than just commercial fishing. Ocean bacteria are
important for the well-being of all marine organisms -- from starfish and sea
horses to seals and dolphins. Directly or indirectly, each depends on bacteria
to help fuel the marine food web.
"If you engineer a bacterium to degrade a pollutant, you hope it will degrade
that pollutant and then die out," the marine scientist said. "You don't
want it to take over the natural role of the other bacteria. If you know what
closely related bacterial strains do when they're released, then maybe you can
design GEMs more effectively, so that the target is attacked, but the impact
on the natural microbiota is minimized."
For the past four years, Hodson and his research team have been taking a close
look at bacteria that have potential as GEMs. They are coming up with some
interesting pieces of a hotly debated puzzle.
The researchers genetically alter native marine bacteria, put them into controlled,
ocean-like environments and then watch to see what happens. After two weeks,
they take samples to see:
- If the bacteria have survived, and if
so, whether their numbers increased, diminished or remained
- How well or poorly these altered microorganisms
adapted to each of a variety of environments, based on their
growth rates and whether
their presence altered those environments in any significant
- Whether the GEMS exchanged genetic material
with other closely related bacteria in the same environments.
Hodson hopes these experiments will help
his research team learn if the altered bacteria have special genetic
characteristics that help
them adapt to high concentrations of certain chemical compounds, especially
common pollutants. For example, an altered organism may possess some
survival characteristics that are only expressed under certain conditions,
much like the human body produces a protective melanin pigment in response
to ultraviolet light.
"When we added a genetically engineered organism, we found under some conditions
that ecosystem-level changes occurred in natural microbial geochemical processes," said
Hodson, who is associate director of UGA's new School of Marine Sciences. BOB,
can you expand this quote with a for instance? Thanks.) "And these changes
are relatively long-term changes; they are sustained over a period of days or
In one such study, Patty Sobecky, one of Hodson's doctoral students, and Dr.
Mark Schell, an associate professor of microbiology, genetically altered a
marine bacterium in the genus Achromobacter to increase its ability to process
phosphate. Then they added it to a model marine system with higher-than-normal
phosphate levels and found that the altered organisms significantly changed
the rate of phosphorous cycling in sea water. Although the researchers did
not have a particular industrial purpose in mind, GEMs with such qualities
could have possible uses in cleaning up phosphates, a common ingredient in
In a similar/related study at the Savannah River Ecology Laboratory, they looked
at freshwater bacteria that possessed a natural ability to break down naphthalene,
a chemical common in dyes and solvents. The research team, which also included
Dr. Mary Ann Moran, assistant professor of marine sciences, studied three (?)
or four (?) (WHICH?) varieties of the same species to see if slight differences
in the genetic make up of the bacteria produced any major differences in their
ability to degrade the naphthalene.
"We wanted to see if small changes would make big differences in how it
survived in a natural environment," Hodson said.
In the laboratory all strains did equally well: They grew fast and maintained
their ability to degrade naphthalene. But when released into the natural environment,
some strains did far better than others.
"Our findings were totally unexpected," Hodson said. "Some of
them would immediately lose the ability to degrade naphthalene; others would
keep it indefinitely. Certain of the strains could adapt to the natural, low-nutrient
environment by growing faster and faster the longer they were exposed, and others
Such studies are needed to assure that any bacterial brooms used to remediate
the environment could be released into natural systems without creating new
problems by altering the ecosystem.
They also help researchers gauge whether groundwater and soils have been contaminated
by industrial wastes in the past and the extent and severity of contamination.
In pristine areas, the population size of these naturally occurring, naphthalene-degrading
bacteria would usually be much smaller than in contaminated areas where naphthalene
is present in greater quantities.
The Lignin Link
Much of Hodson's work is based on his 20-plus years of research on
marine-dwelling bacteria that break down lignin. A component of woody
plants, lignin is the "glue" that
holds wood fibers together and provides support for plant stems, trunks and
Ocean plants don't produce lignin, so all the lignin in the ocean originated
on land. Large amounts are washed into the sea each year in sediments and in
plant materials that grow in salt marshes and along rivers. Unlike terrestrial
systems, the ocean does not have plant-grazing animals like cows, squirrels
and rabbits that can use lignin-rich plants for food. Without lignin-busting
bacteria, this rich food source would go to waste.
Hodson was among the first to show that some marine bacteria not only degrade
or chemically break down lignin, but also release nutrients from lignin-rich
plant material to help fuel the ocean's food web.
More recently, Hodson and Moran have turned their attention to one particular
genus of bacteria known as Streptomyces. Scientists have known for a long time
that Streptomyces are important in breaking down lignin in soil, but no one
even knew if they existed in marine environments.
"We started out by seeing if Streptomyces were present in marine ecosystems," Hodson
said. "There was some debate how important a role they would play even if
they were present.
They now know these bacteria play a significant role in the energy cycle.
"These bacteria are terrific at solubilizing lignin," Moran said. "They
use some of the lignin for growth, and they convert the rest to soluble products
that in turn can be used by other organisms."
"As much as 20 to 30 percent of dissolved organic matter in the near-shore
areas of the southeastern U.S. continental shelf contains traces of plant materials
from terrestrial and salt marsh environments," Hodson said.
Because of its chemical structure, lignin is very resistant to decomposition;
it's an aromatic compound and, therefore, one of the most difficult naturally
occurring compounds to degrade, Hodson said.
"If the organisms that break down lignin can be adapted to break down similar
pollutants, then we have another solution to pollution problems," Hodson
Hodson and Moran are leading a team of researchers who want to see if lignin-degrading
bacteria can be altered to break down other similar aromatic compounds that
are also typical pollutants: phenol, benzene and other common components of
paints and petroleum. In recently initiated experiments, the group is manipulating
the model marine system to see if Streptomyces responds to the addition of
"We have several questions to ask," Moran said. "What happens
to the aromatic compounds once they get in an ocean ecosystem? What organisms
are breaking down the petroleum and the benzene? And what might we learn from
the natural breakdown of lignin that could be applied to these other substances?
We don't have answers yet, but it's a real promising area."
It's also promising for land-based industries. For example, lignin creates
the main problem in waste from the pulp and paper industry. Paper manufacturers
traditionally have used toxic chemicals like chlorine to separate the stubborn
lignin from woody fibers. Chlorine also makes the fibers bright white and more
absorbent, qualities consumers demand in fine writing paper and paper towels
and facial tissues.
"The pulp and paper industry is always interested in finding new, cheaper
and more effective ways of getting that lignin out so that they can get to the
cellulose fibers," Hodson said. "If you engineer an organism that does
that very well, and it gets into the environment, will it change the rate at
which natural plant material is broken down?
"We're trying to benefit both the environment and industry without harming
the environment or impeding the industry," he said. "Biotic industries
can probably do better by the environment than the old-fashioned, chemical-based
heavy industries that they are going to replace, but they still want an intense
study of each new organism before it's released."
Hodson's team would have an easier time studying and tracking free-floating
GEMs if they had a sure-fire way to identify them instantly. Hundreds, maybe
thousands, of bacterial species might be present in a small sample of ocean
water. And since all bacteria come in only one of three basic shapes, they
all look pretty similar under the microscope.
"There's no way I could study bacterial communities by looking at them under
a microscope," Moran said. "I could be looking at 60 different species
or I could be looking at 60 individuals from the same species, and I can't really
tell. That's a slight exaggeration because there are some morphology differences,
but not many."
Until recently that problem has plagued and frustrated many scientists. However,
Hodson's group is among the first to adapt high-tech molecular methods to identify
"We are trying to develop molecular-level tools to follow the populations
of these GEMs after they're released into the chaotic environment, especially
the marine environment," he said, "and to monitor whether they survive
and can actively grow in these natural settings."
To identify individual cells, they label a certain gene with a "genetic
probe" -- a marker that allows them to distinguish certain one-celled
individuals from all the rest. Once marked, these bacteria stand out from all
others in the sample.
One such technique, called the polymerase chain reaction, tricks designated
cells into amplifying its one lignin-degrading gene into thousands. And thousands
are enough to be detected.
"You can't probe for one gene, but if you could amplify the gene and make
lots of copies and give them all a marker, like making them fluoresce or turn
blue or give off radiation -- something you could see under a microscope or detect
in other ways -- then you could tell which cells have the marked gene for lignin
degradation or whatever," Moran said.
Such high-tech methods, originally developed to track diseased tissues
in humans and animals, have solved other problems for Hodson and Moran. "The
old techniques have taken us as far as they can in several areas. The new
open many possibilities to study the entire bacterial community," Moran
One of those possibilities is the study of optimal growth conditions for
bacteria, which vary substantially among different organisms. Microbiologists
for a long time that organisms that grow well in natural environments are not
necessarily the same ones that grow well in the lab, where competition is scarce
and nutrients are plentiful. "It may well be that the species that are
growing in the lab are weed species -- the crab grass and fire ants of the
ocean," Moran said.
Traditionally, determining optimum growth conditions involved a lot of guess
work; scientists might get only a small number of bacterial species to grow
in a sample that might contain hundreds or thousands.
But molecular probes are far more specific and give researchers a clearer view
of how bacteria are performing in different environments. For example, using
the new technique, Hodson's team now can tell in an instant if a sample contains
the Streptomyces bacterium.
"The probes will hybridize only to Streptomyces RNA, which allows us to
know if Streptomyces is there without having to grow them out with culture techniques," Hodson
said. "By just taking a sample, we know if they are present. Then we can
manipulate the system by adding lignins or polluting compounds to see if the
All of this knowledge is important to scientists who want to ensure that genetically
altered bacteria don't wind up polluting the environment they are engineered
"There's no way to contain ocean-living bacteria," Moran said. "They
drift along wherever the current carries them, and as long as the temperatures
and the nutrients are sufficient, they continue to grow and reproduce."
And the best bacterial brooms may be the ones built to last hours or days instead
Judy Purdy is director of research
communications at the University of Georgia. A former naturalist
with the National Audubon Society,
she holds degrees in journalism, biology and botany and has published
a book on medicinal plants.
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