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J. Bacteriol., 03 1997, 1924-1930, Vol 179, No. 6
DB McKay, M Seeger, M Zielinski, B Hofer and KN Timmis
The bphA1A2A3A4 gene cluster, encoding a biphenyl dioxygenase from
Rhodococcus globerulus P6, a gram-positive microorganism able to degrade a
wide spectrum of polychlorobiphenyls (PCBs), was expressed in Pseudomonas
putida, thereby allowing characterization of chlorobiphenyl oxidation by
this enzyme. While P6 biphenyl dioxygenase activity was observed in P.
putida containing bphA1A2A3A4, no activity was detected in Escherichia coli
cells containing the same gene cluster. In E. coli, transcription of genes
bphB and bphCl, located downstream of bphA1A2A3A4, was shown to be driven
solely by a vector promoter, which indicated that the lack of biphenyl
dioxygenase activity was not due to a lack of mRNA synthesis. Radioactive
labelling of bph gene products in E. coli implied inefficient translation
of the bphA gene cluster or rapid degradation of the gene products. The
biosynthesis of functional P6 biphenyl dioxygenase in P. putida cells
containing the same plasmid construct that yielded no activity in E. coli
emphasizes the importance of the host strain for heterologous expression
and shows that synthesis, correct folding, and assembly of a Rhodococcus
biphenyl dioxygenase can be achieved in a gram-negative organism.
Dioxygenation of six mono- and dichlorinated PCB congeners by P. putida
containing the P6 bphA gene cluster indicates the following ring
substitution preference for this reaction (from most to least preferred):
un-, meta- , para-, and ortho-substitution. No indications were found for
dioxygenation of meta/para carbon pairs, or for hydroxylation of
chlorinated carbons at any position of a monochlorinated ring, suggesting a
strict specificity of this biphenyl dioxygenase for attack at
nonhalogenated ortho/meta vicinal carbons. This contrasts the properties of
an analogous enzyme from Pseudomonas sp. strain LB400, which can both
dioxygenate at meta and para positions and dehalogenate substituted ortho
carbons during ortho and meta dioxygenation.
Copyright © 1997, American Society for Microbiology
Heterologous expression of biphenyl dioxygenase-encoding genes from a gram-positive broad-spectrum polychlorinated biphenyl degrader and characterization of chlorobiphenyl oxidation by the gene products
Department of Microbiology, Gesellschaft fur Biotechnologische Forschung, Braunschweig, Germany.
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