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Journal of Bacteriology, April 1999, p. 2535-2547, Vol. 181, No. 8
Cardiff School of Biosciences, Cardiff
University, Cardiff, CF1 3TL, Wales, United Kingdom
Received 1 September 1998/Accepted 29 January 1999
Dehalogenases are key enzymes in the metabolism of halo-organic
compounds. This paper describes a systematic approach to the isolation and molecular analysis of two families of bacterial
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Investigation of Two Evolutionarily Unrelated
Halocarboxylic Acid Dehalogenase Gene Families
-halocarboxylic acid (
HA) dehalogenase genes, called group
I and group II deh genes. The two families are
evolutionarily unrelated and together represent almost all of the
HA
deh genes described to date. We report the design and
evaluation of degenerate PCR primer pairs for the separate
amplification and isolation of group I and II deh
genes. Amino acid sequences derived from 10 of 11 group I
deh partial gene products of new and previously
reported bacterial isolates showed conservation of five residues
previously identified as essential for activity. The exception, DehD
from a Rhizobium sp., had only two of these five residues.
Group II deh gene sequences were amplified from 54 newly isolated strains, and seven of these sequences were cloned
and fully characterized. Group II dehalogenases were stereoselective,
dechlorinating L- but not D-2-chloropropionic
acid, and derived amino acid sequences for all of the genes except
dehII°P11 showed conservation of
previously identified essential residues. Molecular analysis of the two
deh families highlighted four subdivisions in each,
which were supported by high bootstrap values in phylogenetic trees and
by enzyme structure-function considerations. Group I
deh genes included two putative cryptic or silent
genes, dehI°PP3 and
dehI°17a, produced by different organisms. Group II deh genes included two cryptic
genes and an active gene, dehIIPP3, that
can be switched off and on. All
HA-degrading bacteria so far
described were Proteobacteria, a result that may be
explained by limitations either in the host range for
deh genes or in isolation methods.
*
Corresponding author. Mailing address: Cardiff School
of Biosciences, Cardiff University, P.O. Box 915, Cardiff, CF1 3TL, Wales, United Kingdom. Phone: 44 (0)1222 874309. Fax: 44 (0)1222 874305.E-mailmarchesi{at}cardiff.ac.uk.
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