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Appl. Environ. Microbiol. doi:10.1128/AEM.02748-06
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

A novel reductive dehalogenase, identified in a contaminated groundwater enrichment culture and in Desulfitobacterium dichloroeliminans strain DCA1, is linked to dehalogenation of 1,2-dichloroethane

DISTAM, Dipartimento di Scienze e Tecnologie alimentari e Microbiologiche, Università degli Studi di Milano, 20133, Milan, Italy; EniTecnologie, Bio Dept., 20097, San Donato Milanese, Italy; and Laboratory for Microbial Ecology and Technology (LabMET), Ghent University, B-9000 Ghent, Belgium

^* To whom correspondence should be addressed. Email: daniele.daffonchio{at}unimi.it.

	Abstract

A mixed culture dechlorinating 1,2-dichloroethane (1,2-DCA) to ethene was enriched from a long term contaminated groundwater. In the metagenome of the enrichment, a seven-kb reductive dehalogenase (RD) gene cluster sequence was detected by inverse and direct PCR. The RD gene cluster had four open reading frames (ORF) showing 99% nucleotide identity with pceB, pceC, pceT and orf1 of Dehalobacter restrictus strain DSMZ 9455^T, a bacterium able to dechlorinate chlorinated ethenes. However, dcaA, the ORF encoding the catalytic subunit showed only 94% nucleotide and 90% amino acid identity with pceA of strain DSMZ 9455^T. Fifty-three percent of the amino acid differences were localized in two defined regions of the predicted protein. Exposure of the culture to 1,2-DCA and lactate increased the dcaA gene copy number with 2 log units and in these conditions the dcaA and dcaB genes were actively transcribed. A very similar RD gene cluster with 98% identity in the dcaA gene sequence was identified in Desulfitobacterium dichloroeliminans strain DCA1 the only known isolate that selectively dechlorinates 1,2-DCA but not chlorinated ethenes. The dcaA gene of strain DCA1 shares the same amino acid motifs as the new dcaA gene. Southern hybridization on total genomic DNA of strain DCA1 with dcaA gene-specific, and dcaB/pceB-targeting probes, indicated two identical or highly similar dehalogenase gene clusters. In conclusion, these data suggest that the newly described RDs are specifically adapted to 1,2-DCA dechlorination.