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Appl. Environ. Microbiol., May 1995, 1946-1952, Vol 61, No. 5
GM Brazil, L Kenefick, M Callanan, A Haro, V de Lorenzo, DN Dowling and F O'Gara
The genetically engineered transposon TnPCB, contains genes (bph) encoding
the biphenyl degradative pathway. TnPCB was stably inserted into the
chromosome of two different rhizosphere pseudomonads. One genetically
modified strain, Pseudomonas fluorescens F113pcb, was characterized in
detail and found to be unaltered in important parameters such as growth
rate and production of secondary metabolites. The expression of the
heterologous bph genes in F113pcb was confirmed by the ability of the
genetically modified microorganism to utilize biphenyl as a sole carbon
source. The introduced trait remained stable in laboratory experiments, and
no bph-negative isolates were found after extensive subculture in
nonselective media. The bph trait was also stable in nonselective
rhizosphere microcosms. Rhizosphere competence of the modified F113pcb was
assessed in colonization experiments in nonsterile soil microcosms on sugar
beet seedling roots. F113pcb was able to colonize as efficiently as a
marked wild-type strain, and no decrease in competitiveness was observed.
In situ expression of the bph genes in F113pcb was found when F113pcb
bearing a bph'lacZ reporter fusion was inoculated onto sugar beet seeds.
This indicates that the bph gene products may also be present under in situ
conditions. These experiments demonstrated that rhizosphere-adapted
microbes can be genetically manipulated to metabolize novel compounds
without affecting their ecological competence. Expression of the introduced
genes can be detected in the rhizosphere, indicating considerable potential
for the manipulation of the rhizosphere as a self-sustaining biofilm for
the bioremediation of pollutants in soil. Rhizosphere bacteria such as
fluorescent Pseudomonas spp. are ecologically adapted to colonize and
compete in the rhizosphere environment. Expanding the metabolic functions
of such pseudomonads to degrade pollutants may prove to be a useful
strategy for bioremediation.
Copyright © 1995, American Society for Microbiology
Construction of a rhizosphere pseudomonad with potential to degrade polychlorinated biphenyls and detection of bph gene expression in the rhizosphere
Department of Microbiology, University College, Cork, Ireland.
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