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.
A mixed culture dechlorinating 1,2-dichloroethane (1,2-DCA) to ethene was enriched from groundwater that had been subjected to long-term contamination. In the metagenome of the enrichment, a 7-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 by 2 log units, and under 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 possesses the same amino acid motifs as the new dcaA gene. Southern hybridization using total genomic DNA of strain DCA1 with dcaA gene-specific and dcaB- and pceB-targeting probes indicated the presence of 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.
Marzorati
Massimo
M
DESTAM, Dipartimento di Scienze e Tecnologie Alimentari e Microbiologiche, Università degli Studi di Milano, via Celoria 2, 20133 Milano, Italy.
de Ferra
Francesca
F
Van Raemdonck
Hilde
H
Borin
Sara
S
Allifranchini
Elena
E
Carpani
Giovanna
G
Serbolisca
Luca
L
Verstraete
Willy
W
Boon
Nico
N
Daffonchio
Daniele
D
D000595:Amino Acid Sequence; D001483:Base Sequence; D015139:Blotting, Southern; D016000:Cluster Analysis; D017931:DNA Primers; D045858:Desulfitobacterium / Q000201:enzymology*; D005025:Ethylene Dichlorides / Q000378:metabolism*; D005618:Fresh Water / Q000382:microbiology*; D007558:Italy; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D010088:Oxidoreductases / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017385:Sequence Homology; D014874:Water Pollutants, Chemical / Q000378:metabolism*
D017931:DNA Primers; D005025:Ethylene Dichlorides; D014874:Water Pollutants, Chemical; C024565:ethylene dichloride; D010088:Oxidoreductases