Applied and Environmental Microbiology, May 1999, p. 2151-2162, Vol. 65, No. 5
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Center for Microbial Ecology,1 Department of Crop and Soil Sciences,2 and Department of Microbiology,3 Michigan State University, East Lansing, Michigan 48824
Received 25 September 1998/Accepted 18 February 1999
We have cloned and characterized novel oxygenolytic
ortho-dehalogenation (ohb) genes from
2-chlorobenzoate (2-CBA)- and 2,4-dichlorobenzoate (2,4-dCBA)-degrading
Pseudomonas aeruginosa 142. Among 3,700 Escherichia coli recombinants, two clones, DH5
F'(pOD22) and
DH5
F'(pOD33), converted 2-CBA to catechol and 2,4-dCBA and 2,5-dCBA
to 4-chlorocatechol. A subclone of pOD33, plasmid pE43, containing the
3,687-bp minimized ohb DNA region conferred to P. putida PB2440 the ability to grow on 2-CBA as a sole carbon
source. Strain PB2440(pE43) also oxidized but did not grow on 2,4-dCBA,
2,5-dCBA, or 2,6-dCBA. Terminal oxidoreductase ISPOHB
structural genes ohbA and ohbB, which encode polypeptides with molecular masses of 20,253 Da (
-ISP) and 48,243 Da
(
-ISP), respectively, were identified; these proteins are in accord
with the 22- and 48-kDa (as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis) polypeptides synthesized in
E. coli and P. aeruginosa parental strain 142. The ortho-halobenzoate 1,2-dioxygenase activity was
manifested in the absence of ferredoxin and reductase genes, suggesting
that the ISPOHB utilized electron transfer components
provided by the heterologous hosts. ISPOHB formed a new
phylogenetic cluster that includes aromatic oxygenases featuring
atypical structural-functional organization and is distant from the
other members of the family of primary aromatic oxygenases. A putative
IclR-type regulatory gene (ohbR) was located upstream of
the ohbAB genes. An open reading frame (ohbC)
of unknown function that overlaps lengthwise with ohbB but
is transcribed in the opposite direction was found. The
ohbC gene codes for a 48,969-Da polypeptide, in accord with
the 49-kDa protein detected in E. coli. The ohb genes are flanked by an IS1396-like sequence containing a
putative gene for a 39,715-Da transposase A (tnpA) at
positions 4731 to 5747 and a putative gene for a 45,247-Da DNA
topoisomerase I/III (top) at positions 346 to 1563. The
ohb DNA region is bordered by 14-bp imperfect inverted
repeats at positions 56 to 69 and 5984 to 5997.
Present address: Institute of Ecology and Genetics of
Microorganisms, Russian Academy of Sciences, Ural Branch, Perm 614081, Russia.
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