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Lessons Aquatic
Microbes Can Teach

Ground Truth

Becker finishes with her students in the lab. She has not definitively pinpointed the source of contamination, but she has identified some other problems with their protocol. For example, she notices that the iron solution that is added to the culture has turned orange, indicating that the solution was prematurely exposed to air. Iron helps sop up oxygen, which is harmful to the bacteria, explains Becker. Since this solution had already been in contact with air, it would not be effective at scavenging oxygen in the culture media.

"This is why it is good to get down to the lab," she says.

Becker takes her job as graduate mentor seriously. She has five graduate students and a post-doctoral fellow, and she meets with each one individually every Friday. She helps them to evaluate their work from the previous week and set goals for the next one. By the end of each Friday, her head is spinning but she feels that these meetings really help her students stay on track.

Every other week, her lab meets as a group to hear a presentation from one of its members. Now Becker hurries upstairs from the lab to a classroom to listen to one of her Ph.D. students, Deyang Huang, talk about his recent experiments. Huang is studying how fast another PCE-breather (Desulfitobacterium sp. strain PCE1) can carry out certain reactions. Unlike D. ethenogenes, strain PCE1 cannot completely detoxify PCE. This bug instead converts PCE to the related compound TCE. Bacteria such as strain PCE1 thrive at contaminated sites and can also contribute to the removal of PCE from groundwater, Becker explains. But these bugs may also divert resources, including PCE, away from other potentially important organisms like D. ethenogenes.

Huang's results leave Becker a little puzzled. The reaction rates that he measured in these so-called kinetic experiments do not seem to match the values that she has extrapolated from the scientific literature for her mathematical model. His data also show that the rate at which the bug breathes and metabolizes PCE depends on the age of the source culture, a likely indication that the culture had not achieved the desired "steady state" before he began the experiment. Although Huang's data are not conclusive, Becker expects that the experiment, which took months to complete, will need to be repeated before the results can be interpreted.

Meanwhile in a subterranean aquifer beneath former Kings Cleaners in Towson, roughly 60 miles north of Becker's lab, PCE persists in the groundwater at high concentrations, even as changes begin to unfold aboveground. Soon ABC Rentals, a business that rents tools and hardware, will build a warehouse on the part of the site where the bowling alley once stood. The footprint of the dry cleaners remains unclaimed as of yet, but several companies have placed bids for the space, says Debbie Haney, the broker handling the property for Mackenzie Commercial Real Estate Services.

The microbial goings-on beneath the former Kings Cleaners remain a mystery. Perhaps D. ethenogenes is already hard at work underground, respiring the toxin PCE and rendering it harmless. Or maybe the PCE-breather is nowhere to be found in this groundwater. Or perhaps other bacteria have beaten it to the punch, stealing the necessary resources and depriving it of the opportunity to work its metabolic magic. With each experiment, Becker's research unlocks new clues to how these microbes behave on their home turf, clues that will ultimately improve our ability to readily clean up contaminated groundwater. Her research findings will come too late to change the course of action for the site on East Joppa Road in Towson. But plenty of PCE-contaminated sites all over the country still need to be cleaned up. A clearer understanding of microbial competition promises to help the bioremediation industry encourage bacteria to do what they do — even better.

For More Information

Jennifer Becker and PCE

Becker Lab Home Page
PCE Factsheet from the U.S. Environmental Protection Agency
TCE Factsheet from the U.S. Environmental Protection Agency
wwww.epa.gov/safewater/contaminants/ dw_contamfs/trichlor.html
State Coalition for Remediation of Drycleaners

Kevin Sowers and PCBs

Kevin Sowers Lab
EPA site on Hudson River dredging
Chesapeake Bay Program Indicators
EPA Indicators for Chesapeake Bay Health

Robert Belas and Microbes

Robert BelasÕs Lab

Russell Hill and Medicines

Russell HillÕs Lab

Ronald Weiner and NSF

Research Profile
National Science Foundation Cellular Systems Cluster


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