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Fall 1993

Research Magazine > ARCHIVE > Fall 93 > Article

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 up.

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 middle."

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."

Crafting GEMs

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 the same.
  • 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 ways.
  • 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 weeks."

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 many detergents.

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 could not."

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 leaves.

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 said.

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 aromatic compounds.

"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."

Genetic Probes

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 bacteria.

"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 ones open many possibilities to study the entire bacterial community," Moran said.

One of those possibilities is the study of optimal growth conditions for bacteria, which vary substantially among different organisms. Microbiologists have known 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 system responds."

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 to protect.

"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 of years.

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.

For more information e-mail rhodson@uga.cc.uga.edu

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