Scientists Decipher Genome of Bacterium that Helps Clean Up Major Groundwater Pollutants


Scientists at the Institute for Genomic Research (TIGR) in Rockville, MD, have deciphered the genome sequence of a microbe that can be used to clean up pollution by chlorinated solvents a major category of groundwater contaminants that are often left as byproducts of dry cleaning or industrial production. The work is to be published in Science on Friday, January 7. The study of the DNA sequence of Dehalococcoides ethenogenes found evidence that the soil bacterium may have developed the metabolic capability to consume chlorinated solvents fairly recently possibly by acquiring genes from a neighboring microbe in order to survive the increased prevalence of the pollutants. The microbe which was discovered by Steve Zinder at Cornell University at a sewage treatment plant in Ithaca, NY, is the only known microbe that is known to reductively dechlorinate the pervasive groundwater pollutants tetrachloroethelene (PCE) and trichloroethylene (TCE). The end result is a nontoxic byproduct, ethene. Another major collaborator was Lorenz Adrian of the Institute for Biotechnology at the Technical University of Berlin, Germany. The D. ethenogenes project was sponsored by the U.S. Department of Energy’s Office of Biological and Environmental Research. Today, environmental consulting companies are using Dehaloccocoides cultures to assure remediation at numerous sites contaminated by PCE or TCE by one count, there are at least 17 Dehaloccocoides bioremediation sites in ten states, including Texas, Delaware and New Jersey. Dehalococcoides ethenogenes turns out to have 19 different reductive dehalogenases (RDs) which allow the microbe to “breathe” chlorinated solvents. Those RDs, in combination with the bacterium’s five hydrogenase complexes and its severely limited repertoire of other metabolic modes, show that D. ethenogenes is highly specialized for respiratory reductive dechlorination using hydrogen as the electron donor. By comparing the genomic sequence of D. ethenogenes with that of other Dehalococcoides spp. and related organisms that have different capabilities and spectra for dehalogenation, scientists should be able to deepen the understanding of the chemical process and the best ways to use microbes in the bioremediation of sites that are contaminated with halogenated organic compounds. The genome of D. ethenogenes is the first complete sequence from the green nonsulfur group of bacteria. By comparing its genome sequence with that of the more than 50 other species sequenced at TIGR, scientists have learned more about the phylogenetic diversity of microbes.