Ca. Lajoie et al., COMETABOLIC OXIDATION OF POLYCHLORINATED-BIPHENYLS IN SOIL WITH A SURFACTANT-BASED FIELD APPLICATION VECTOR, Applied and environmental microbiology, 60(8), 1994, pp. 2826-2833
Polychlorinated biphenyl (PCB)-degradative genes, under the control of
a constitutive promoter, were cloned into a broad-host-range plasmid
and a transposon. These constructs were inserted into a surfactant-uti
lizing strain, Pseudomonas putida IPL5, to create a field application
vector (FAV) in which a surfactant-degrading organism cometabolizes PC
B. By utilizing a surfactant not readily available to indigenous popul
ations and a constitutive promoter, selective growth and PCB degradati
ve gene expression are decoupled from biphenyl. Since PCB degradation
via the biphenyl degradation pathway is nonadaptive in the absence of
biphenyl, there is no selective pressure for PCB gene maintenance. The
recombinant strains exhibited degradative activity against 25 of 33 P
CB congeners in Aroclor 1248 in the absence of biphenyl. Whole-cell en
zyme assays indicated that PCB-degradative activity of a recombinant s
train carrying the PCB genes on a plasmid was approximately twice that
of the same strain carrying the PCB genes on a transposon. Plasmid lo
ss rates in the absence of antibiotic selection averaged 7.4% per cell
division and were highly variable between experiments. Surfactant-ame
nded slurries of PCB-contaminated electric power plant substation soil
were inoculated with approximately 10(5) recombinant cells per ml. Th
e populations of the added strains increased to greater than 10(9) cel
ls per ml in 2 days, and cell growth coincided,vith PCB degradation. B
y 15 days, 50 to 60% of the indicator congener 2,3,2',5'-tetrachlorobi
phenyl was degraded. The effectiveness of PCB degradation by the plasm
id-containing strain depended on plasmid stability. The transposon enc
oded PCB genes were much more stable, and in surfactant-amended soil s
lurries, PCB degradation was more consistent between experiments.