Bacterium Could Treat PCBs Without the Need for Dredging
Scanning electron micrographs of
Credit: F. E. Löeffler. 2007. Appl. Envir. Microbiol.
2007 : AEM.02909-06v1 Copyright 2007, American Society
You might want to reconsider your feelings about bacteria.
These microscopic creatures have been assaulted by hand soap
and smelly antibacterial gels, but a shining star among these
organisms could one day transform the way we remove
polychlorinated biphenyls (PCBs) from our environment.
Rensselaer researchers have discovered an organism that could
be the key to developing methods that help detoxify commercial
PCB compounds on site — without the need for dredging.
The results will appear in the April 15 issue of Applied
and Environmental Microbiology.
Commercial PCBs, which were banned from production in the
United States in 1977, were once commonly used by industry. To
date, the most commonly used method to remove PCBs from the
environment is to dredge and then deposit the sediments in a
In order to detoxify PCBs the strong bonds between the
chlorine atoms and the biphenyl compounds that make up the PCB
atomic structure need to be broken, a process known as
dechlorination. More than two decades ago, scientists
discovered that PCBs were slowly being dechlorinated by
naturally occurring microbes, but despite years of research,
the exact microbes responsible have remained elusive — until
Research Professor of Biology Donna Bedard analyzed
sediments from the Housatonic River in Massachusetts — an area
known to be contaminated with PCBs — to develop sediment-free
cultures and to identify the bacteria that were breaking down
the PCBs. Using molecular techniques, the research team
determined that the microbes that are dechlorinating the PCBs
belong to a group of bacteria known as Dehalococcoides
Dhc are “strict anaerobic” bacteria, which means
they cannot survive in the presence of oxygen. This is the
first time it has been demonstrated that Dhc can
dechlorinate complex commercial PCB mixtures. The discovery of
the Dhc bacteria’s unique abilities could one day
alter the way we treat PCB contaminated water bodies.
After identifying the Dhc bacteria, Bedard and her
team proved that the anaerobic bacteria thrive on the PCBs,
much as humans thrive on oxygen. The microbes replace the
chlorines on the PCBs with hydrogen, which fuels their growth
and begins the PCB degradation process.
The research was funded through a grant from the National
Science Foundation. Bedard was assisted in her research by
Kristi Ritalahti and Frank Löeffler of the Georgia Institute of