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Applied and Environmental Microbiology, November 1998, p. 4185-4193, Vol. 64, No. 11
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Evolution of a Pathway for Chlorobenzene Metabolism Leads to Natural Attenuation in Contaminated Groundwater

Jan Roelof van der Meer,1 Christoph Werlen,1 Shirley F. Nishino,2 and Jim C. Spain2,*

Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH 8600 Dübendorf, Switzerland,1 and Air Force Research Laboratory/MLQR, Tyndall Air Force Base, Florida 32403-53232

Received 1 May 1998/Accepted 18 August 1998

Complete metabolism of chlorinated benzenes is not a feature that is generally found in aerobic bacteria but is thought to be due to a novel recombination of two separate gene clusters. Such a recombination could be responsible for adaptation of a natural microbial community in response to contamination with synthetic chemicals. This hypothesis was tested in a chlorobenzene (CB)-contaminated aquifer. CB-degrading bacteria from a contaminated site were characterized for a number of years by examining a combination of growth characteristics and DNA-DNA hybridization, PCR, and DNA sequence data. The genetic information obtained for the CB pathway of the predominant microorganism, Ralstonia sp. strain JS705, revealed a unique combination of (partially duplicated) genes for chlorocatechol degradation and genes for a benzene-toluene type of aromatic ring dioxygenase. The organism was detected in CB-polluted groundwater by hybridizing colonies cultivated on low-strength heterotrophic media with probes for the CB pathway. Southern hybridizations performed to determine the organization of the CB pathway genes and the 16S ribosomal DNA indicated that CB-degrading organisms isolated from different wells at the site were identical to JS705. Physiological characterization by the Biolog test system revealed some differences. The genes for the aromatic ring dioxygenase and dihydrodiol dehydrogenase of JS705 were detected in toluene and benzene degraders from the same site. Our results suggest that recent horizontal gene transfer and genetic recombination of existing genes between indigenous microorganisms were the mechanisms for evolution of the catabolic pathway. Evolution of the CB pathway seems to have created the capacity for natural attenuation of CB at the contaminated site.

* Corresponding author. Mailing address: Air Force Research Laboratory/MLQR, 139 Barnes Dr., Ste. 2, Tyndall AFB, FL 32403-5323. Phone: (850) 283-6058. Fax: (850) 283-6090. E-mail: JSpain{at}ccmail.aleq.tyndall.af.mil.

Applied and Environmental Microbiology, November 1998, p. 4185-4193, Vol. 64, No. 11
0099-2240/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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