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Appl. Environ. Microbiol., Apr 1997, 1523-1530, Vol 63, No. 4
MR Fries, LJ Forney and JM Tiedje
We characterized the bacterial populations that grew in a Moffett Field,
Calif., aquifer following three sequential field tests of phenol- or
toluene-driven cometabolism of trichloroethene (TCE). Reducing the toluene
and phenol concentrations in most-probable-number (MPN) tubes from 50 to 5
ppm increased the population density measured for these degraders by 1.5
and 1 log units, respectively, suggesting that natural populations might be
quite sensitive to these substrates. Phenol and toluene degraders were
isolated from the terminal MPN dilution tubes; 63 genetically distinct
strains were identified among the 273 phenol- and toluene-degrading
isolates obtained. TCE was cometabolized by 60% of the genetically distinct
strains. Most strains (57%) grew on both phenol and toluene, and 78% of
these strains hybridized to the toluene ortho-monooxygenase (TOM) probe.
None of the strains hybridized to probes from the four other toluene
oxygenase pathways. Gram-positive strains comprised 30% of the collection;
all of these grew on phenol, and 47% of them also grew on toluene, but none
hybridized to the TOM probe. Among the gram-negative strains, 86% of those
that grew on both toluene and phenol hybridized to the TOM probe, while
only 5% of those that were TOM-positive grew on toluene alone. A larger
proportion of TCE degraders was found among gram-negative than
gram-positive strains and among organisms that grew on phenol than those
that grew on toluene. Hybridization of strains to the TOM probe was
somewhat predictive of their TCE-cometabolizing ability, especially for
strains isolated on toluene, but there was also a significant number (20%)
of strains that hybridized to the TOM probe but were poor TCE cooxidizers.
No Moffett Field isolates were as effective as Burkholderia cepacia G4 in
cooxidizing TCE. Most of the aquifer strains ranged from moderately
effective to ineffective in TCE cooxidation. Such populations, however,
apparently accounted for the successful phenol- and toluene-stimulated TCE
removal that occurred during the field assessment of this remediation
process. This suggests that naturally occurring communities of only
moderate TCE-cooxidizing ability may support successful TCE bioremediation
as long as the phenol or toluene present is not limiting. This activity,
however, may not be sustainable for the long term, because TCE-inactive
populations that consumed toluene at rates equal to that of the best TCE
degraders were present and hence would be expected to eventually dominate
the community.
Copyright © 1997, American Society for Microbiology
Phenol- and Toluene-Degrading Microbial Populations from an Aquifer in Which Successful Trichloroethene Cometabolism Occurred
Center for Microbial Ecology and Departments of Crop and Soil Sciences and of Microbiology, Michigan State University, East Lansing, Michigan 48824
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