Scanning electron micrographs of Dehalococcoides Credit: F. E. Löeffler. 2007. Appl. Envir. Microbiol. 2007 : AEM.02909-06v1 Copyright 2007, American Society for Microbiology

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 landfill. 

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 now.

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). 

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 Technology.

Published March 12, 2007