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Appl. Environ. Microbiol., Sep 1995, 3336-3346, Vol 61, No. 9
GR Johnson and RH Olsen
It was previously shown by others that Pseudomonas sp. strain JS150
metabolizes benzene and alkyl- and chloro-substituted benzenes by using
dioxygenase-initiated pathways coupled with multiple downstream metabolic
pathways to accommodate catechol metabolism. By cloning genes encoding
benzene-degradative enzymes, we found that strain JS150 also carries genes
for a toluene/benzene-2-monooxygenase. The gene cluster encoding a
2-monooxygenase and its cognate regulator was cloned from a plasmid carried
by strain JS150. Oxygen (18O2) incorporation experiments using Pseudomonas
aeruginosa strains that carried the cloned genes confirmed that toluene
hydroxylation was catalyzed through an authentic monooxygenase reaction to
yield ortho-cresol. Regions encoding the toluene-2-monooxygenase and
regulatory gene product were localized in two regions of the cloned
fragment. The nucleotide sequence of the toluene/benzene-2-monooxygenase
locus was determined. Analysis of this sequence revealed six open reading
frames that were then designated tbmA, tbmB, tbmC, tbmD, tbmE, and tbmF.
The deduced amino acid sequences for these genes showed the presence of
motifs similar to well-conserved functional domains of multicomponent
oxygenases. This analysis allowed the tentative identification of two
terminal oxygenase subunits (TbmB and TbmD) and an electron transport
protein (TbmF) for the monooxygenase enzyme. In addition to these gene
products, all the tbm polypeptides shared significant homology with protein
components from other bacterial multicomponent monooxygenases. Overall, the
tbm gene products shared greater similarity with polypeptides from the
phenol hydroxylases of Pseudomonas putida CF600, P35X, and BH than with
those from the toluene monooxygenases of Pseudomonas mendocina KR1 and
Burkholderia (Pseudomonas) pickettii PKO1. The relationship found between
the phenol hydroxylases and a toluene-2-monooxygenase, characterized in
this study for the first time at the nucleotide sequence level, suggested
that DNA probes used for surveys of environmental populations should be
carefully selected to reflect DNA sequences corresponding to the metabolic
pathway of interest.
Copyright © 1995, American Society for Microbiology
Nucleotide sequence analysis of genes encoding a toluene/benzene-2- monooxygenase from Pseudomonas sp. strain JS150
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620, USA.
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