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DR. KEVIN SOWERS - University of Maryland, Center of Marine Biotechnology (COMB)
The Research: PCB Eaters and Methane Makers
Kevin Sowers' research program revolves around marine microbes, mainly those that are anaerobic, growing in the absence of oxygen. Most of the anaerobes he works with are found in ocean sediments or in marsh areas. His team was one of the first to focus on these marine organisms, and has developed some unique capabilities for their study.
Though they have worked in various areas and environments, the Sowers team's work focuses on two primary areas: anaerobes capable of breaking down toxic polychlorinated biphenyls (PCBs), offering a potential path for clean-up of areas contaminated by these toxic compounds, and methanogens, which break down organic waste to produce methane. Methanogenesis is of interest both because it might be harnessed as a means of processing waste, and because methane is a powerful greenhouse gas, meaning that methane produced by these organisms can play roles in climate change.
 - VIDEO CLIP 1: "Research Focus On Anaerobic Marine Microbes"
 Anaerobic Basics
Anaerobes have a unique niche in the ecology of the oceans by complementing the processes that go on in associated oxygenated (aerobic) environments. For instance, if certain nutrients or even the remains of a fish are not completely consumed in sediments before all available oxygen is used up, then the anaerobes take over the work. "The anaerobes essentially complete the process of degradation," says Sowers. They convert organic carbon, nitrogen, and other components into carbon dioxide and other compounds that are then recycled back into the environment.
Anaerobic microbes have been studied far less than aerobes largely for the simple reason that it is more difficult to create and maintain an oxygen-free environment for experiments. Anaerobes also tend to be extremely slow growing, which further complicates their study. However, researchers are now able to create the same types of experiments with the anaerobes that are conducted with aerobic microbes, primarily by working in airtight glove boxes flushed with gases such as carbon dioxide or nitrogen rather than air. The Sowers group also has large anaerobic fermentation units for the mass-culture of microbes.
Enlisting Microbes to Clean Up PCBs
Polychlorinated biphenyls (PCBs) are a worldwide environmental contamination problem. Production of these very heat-stable compounds began in the 1930s for a variety of purposes related to their stability, such as cooling transformers and use in high-voltage relays and fuses. Though banned in the 1970s, the very stability that made them useful for commercial applications has created a persistent problem because they pose a number of health risks but degrade very slowly.
Currently, all options for PCB contamination clean up are extremely costly and time-consuming. Contaminated sediments have to be removed through dredging and then either burned to eliminate the PCBs, or buried to contain them. Needless to say, a biological method for effectively and safely breaking down PCBs in situ to avoid such high cost and difficulty would be extremely valuable, both economically and environmentally.
On a path of hopefully developing such a method, the Sowers group has found a number of anaerobic organisms that will break down the PCBs. But, they do it very slowly using a process called reductive dechlorination. This is essentially stripping the chlorines from these compounds, thus reducing their toxicity. The organisms the group works with are found in both marine and estuarine sediments. Prior to Sowers' focus on these environments, research on organisms that break down the PCBs was focused on freshwater rivers.
Researchers had known for some time that there were organisms that broke down PCBs, but they didn't know which organisms, and finding them was a challenge because the anaerobes are so difficult to culture. Rather than using a classical microbiology approach, as had been done in the past, Sowers used molecular approaches to identify the organisms breaking down the PCBs.
The team began with Baltimore Harbor sediment samples, to which they added PCBs. They zeroed in on the organisms by changing growth mediums and other conditions until, by process of elimination, they eventually were able to get the organisms into pure cultures of, or cultures highly enriched in, the organisms breaking down the PCBs. Once the organisms were isolated, Sowers and his team were able to develop molecular probes specific to unique sequences in their DNA, which allows the identification of even very small concentrations of these anaerobes in samples. Using this technique they are able to identify which PCB dechlorinators are present in sediments from a given location, and in what concentrations, without the challenge of isolating or culturing the organisms.
Sowers sees a number of ways research on the PCB dechlorinators might ultimately lead to methods for breaking down and eliminating PCB contamination and associated environmental and health hazards. One possibility is that through ongoing research to understand the organisms' physiology, biochemistry, and genomics, they might be able to identify ways to stimulate the breakdown process naturally or to grow the organisms and add them to sediments in need of decontamination, an environmental bioremediation [int link: http://www.marinebiotech.org/biorem.html] process known as bioaugmentation. Another possibility is that through genomics they might identify key enzymes in the dechlorination and then produce these enzymes and add them to sediments to speed up the otherwise slow natural decontamination process. The work is still in its early stages, however, and development and application of an effective technique is likely some years off.
- VIDEO CLIP 2: "Biological Dechlorination Of PCB Pollutants In Marine Systems"
- VIDEO CLIP 3: "Detecting And Identifying The Key Dechlorinator Organisms"
The Benefits of Methane Production
Sowers' second main anaerobic interest is the production of methane by the Archaea.
These are single celled organisms now classified as distinct from both true bacteria and eukaryotes
("higher organisms"). Through methanogenesis, the Archaea convert carbon, their main energy source,
to methane, making for a very useful process that researchers are working to harness in a number
of ways. The process is generally accomplished by consortiums of different Archaea working in unison
and takes place both in marine and terrestrial sediments.
Sowers' is studying all aspects of the basic biology of methanogensis, from the physiology of
methanogens to their genomics, with an overall goal of determining ways to optimize the process
for applications such as treating sewage sludge or waste from aquaculture facilities. Once such waste
carbon is converted to methane, the gas could either be burned as a fuel, or oxidized to carbon dioxide.
Because of the energy production potential of methanogenesis, the Department of Energy's Joint Genome
Institute (JGI) accepted a proposal from Sowers to sequence the entire genome of the methanogen Methanosarcina barkeri fusaro,
originally isolated from freshwater mud. The overall goal of such ongoing sequencing work is to increase understanding of microbial
energy production mechanisms to ultimately use them in the production of clean, renewable energy. Sowers' methanogen
project marked the 100th genome to be sequenced by JGI.
- VIDEO CLIP 4: "Marine Methanogenesis And The Archaea"
The Pitfalls of Methane Production; Extraterrestrial Methane
The Sowers team is also interested in understanding how methanogenesis proceeds in cold temperatures, a topic they have explored at locations such as Baffin Island in Canada and Greenland. Huge amounts of carbon are frozen in such frigid regions in the forms of peat and other plant material. As global warming proceeds, it raises the question of whether such material will become exposed to methanogens. This is a concern because methane is about a dozen times more effective as a greenhouse gas than carbon dioxide. Therefore, substantial new production of methane could create a positive feedback loop that would drive greater climatic warming. Sowers is working to understand methanogenesis at lower temperatures and the organisms responsible for it, in part to aid in prediction of the future impacts of receding ice.
A final interest in the methanogens for Sowers relates to the potential for life on other planets, a topic of growing interest because of recent discoveries of both water and methane on mars. He and his team are working in conjunction with colleagues at the Space Telescope Science Institute to determine the minimal requirements for methanogenic life.
- VIDEO CLIP 5: "High Arctic Research And Cold-Loving Microbes"
Education: An Interest in the Environment
Sowers entered college with an interest in the environment and wondering whether he should pursue biology or chemistry. Though he eventually settled on environmental biology as a major at the State University College at Buffalo in New York, he says he eventually realized the distinctions between the two fields were not great because each still required study of the other. While an undergraduate he became interested in microbiology after his first course on the topic. As a result, he applied to a summer microbial ecology course at the Woods Hole Biological Laboratory, which, he says, focused his attentions on marine microbiology. So, he went on to get his master's in marine microbiology at State University then moved to Virginia Tech and became involved in a methanogenesis research program. From there he went to UCLA to begin looking at the molecular biology of methanogenesis, a new area of research at the time. Sowers took a position at the University of Maryland in 1991 as an assistant professor.
- VIDEO CLIP 6: "An Exciting Time; Educational Background"
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