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Catechol 2,3-dioxygenases functional in oxygen-limited (hypoxic) environments

J J Kukor1, R H Olsen

  • 1Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor 48109-0620, USA.

Applied and Environmental Microbiology
|May 1, 1996
PubMed
Summary

Bacteria from oxygen-limited aquifers degrade toluene using nitrate. Novel Pseudomonas strains possess enhanced enzymes (catechol 2,3-dioxygenase) for efficient toluene breakdown in hypoxic conditions, suggesting new bioremediation strategies.

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Area of Science:

  • Environmental microbiology
  • Bioremediation
  • Biochemistry

Background:

  • Hypoxic (oxygen-limited) environments, common in petroleum-contaminated aquifers, pose challenges for microbial degradation of aromatic hydrocarbons like toluene.
  • Nitrate can serve as an alternative electron acceptor for microbial respiration in anaerobic or oxygen-limited conditions.
  • Toluene degradation pathways typically involve key enzymes like catechol 2,3-dioxygenase (C230).

Purpose of the Study:

  • To investigate toluene degradation by bacteria isolated from hypoxic petroleum-contaminated aquifers.
  • To compare the kinetic properties of catechol 2,3-dioxygenase (C230) in novel nitrate-dependent toluene degraders with those from known toluene degraders.
  • To elucidate the genetic regulation of C230 expression under oxygen-limited conditions.

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Main Methods:

  • Isolation and characterization of toluene-degrading bacteria from hypoxic aquifers.
  • Enzymatic assays to determine kinetic parameters (K(m) and Vmax) of C230.
  • Nucleotide and amino acid sequence analysis of C230 and its upstream regulatory region.
  • Gene expression analysis under varying oxygen conditions.

Main Results:

  • Three Pseudomonas isolates (P. pickettii PKO1, Pseudomonas sp. W31, P. fluorescens CFS215) demonstrated growth on toluene using nitrate in hypoxic environments.
  • C230 from these novel strains exhibited significantly higher oxygen affinity and substrate turnover rates compared to C230 from archetypal toluene degraders.
  • Sequence analysis identified C230 from PKO1 as a novel extradiol dioxygenase and revealed regulatory sequences, including an ANR-binding site homolog, enhancing gene expression under oxygen limitation.

Conclusions:

  • A novel group of microorganisms capable of oxygen-requiring yet nitrate-enhanced degradation of aromatic compounds in hypoxic environments has been identified.
  • Strain PKO1 exemplifies this group, possessing an oxygen-requiring enzyme with optimized kinetics for low-oxygen conditions and regulated gene expression for enhanced enzyme synthesis.
  • These findings suggest potential for novel bioremediation strategies in contaminated hypoxic subsurface environments.