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Appl. Environ. Microbiol., 05 1996, 1728-1740, Vol 62, No. 5
JJ Kukor and RH Olsen
We studied the degradation of toluene for bacteria isolated from hypoxic
(i.e., oxygen-limited) petroleum-contaminated aquifers and compared such
strains with other toluene degraders. Three Pseudomonas isolates, P.
pickettii PKO1, Pseudomonas sp. strain W31, and P. fluorescens CFS215, grew
on toluene when nitrate was present as an alternate electron acceptor in
hypoxic environments. We examined kinetic parameters (K(m) and Vmax) for
catechol 2,3-dioxygenase (C230), a key shared enzyme of the
toluene-degradative pathway for these strains, and compared these
parameters with those for the analogous enzymes from archetypal
toluene-degrading pseudomonads which did not show enhanced,
nitrate-dependent toluene degradation. C230 purified from strains W31,
PKO1, and CFS215 had a significantly greater affinity for oxygen as well as
a significantly greater rate of substrate turnover than found for the
analogous enzymes from the TOL plasmid (pWW0) of Pseudomonas putida PaW1,
from Pseudomonas cepacia G4, or from P. putida F1. Analysis of the
nucleotide and deduced amino acid sequences of C23O from strain PKO1
suggests that this extradiol dioxygenase belongs to a new cluster within
the subfamily of C23Os that preferentially cleave monocyclic substrates.
Moreover, deletion analysis of the nucleotide sequence upstream of the
translational start of the meta-pathway operon that contains tbuE, the gene
that encodes the C230 of strain PKO1, allowed identification of sequences
critical for regulated expression of tbuE, including a sequence homologous
to the ANR-binding site of Pseudomonas aeruginosa PAO. When present in cis,
this site enhanced expression of tbuE under oxygen-limited conditions.
Taken together, these results suggest the occurrence of a novel group of
microorganisms capable of oxygen-requiring but nitrate- enhanced
degradation of benzene, toluene, ethylbenzene, and xylenes in hypoxic
environments. Strain PKO1, which exemplifies this novel group of
microorganisms, compensates for a low-oxygen environment by the development
of an oxygen-requiring enzyme with kinetic parameters favorable to function
in hypoxic environments, as well as by elevating synthesis of such an
enzyme in response to oxygen limitation.
Copyright © 1996, American Society for Microbiology
Catechol 2,3-dioxygenases functional in oxygen-limited (hypoxic) environments
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620, USA.
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