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Synergistic Degradation of Linuron by a Bacterial Consortium and Isolation of a Single Linuron-Degrading Variovorax Strain

Winnie Dejonghe,^1, Ellen Berteloot,¹ Johan Goris,² Nico Boon,¹ Katrien Crul,¹ Siska Maertens,¹ Monica Höfte,³ Paul De Vos,² Willy Verstraete,¹ and Eva M. Top^1,4*

Laboratory of Microbial Ecology and Technology (LabMET),¹ Laboratory of Microbiology,² Laboratory of Phytopathology, Ghent University, B-9000 Ghent, Belgium,³ Department of Biological Sciences, University of Idaho, Moscow, Idaho 83844-3051⁴

Received 30 September 2002/ Accepted 11 December 2002

The bacterial community composition of a linuron-degrading enrichment culture and the role of the individual strains in linuron degradation have been determined by a combination of methods, such as denaturing gradient gel electrophoresis of the total 16S rRNA gene pool, isolation and identification of strains, and biodegradation assays. Three strains, Variovorax sp. strain WDL1, Delftia acidovorans WDL34, and Pseudomonas sp. strain WDL5, were isolated directly from the linuron-degrading culture. In addition, subculture of this enrichment culture on potential intermediates in the degradation pathway of linuron (i.e., N,O-dimethylhydroxylamine and 3-chloroaniline) resulted in the isolation of, respectively, Hyphomicrobium sulfonivorans WDL6 and Comamonas testosteroni WDL7. Of these five strains, only Variovorax sp. strain WDL1 was able to use linuron as the sole source of C, N, and energy. WDL1 first converted linuron to 3,4-dichloroaniline (3,4-DCA), which transiently accumulated in the medium but was subsequently degraded. To the best of our knowledge, this is the first report of a strain that degrades linuron further than the aromatic intermediates. Interestingly, the rate of linuron degradation by strain WDL1 was lower than that for the consortium, but was clearly increased when WDL1 was coinoculated with each of the other four strains. D. acidovorans WDL34 and C. testosteroni WDL7 were found to be responsible for degradation of the intermediate 3,4-DCA, and H. sulfonivorans WDL6 was the only strain able to degrade N,O-dimethylhydroxylamine. The role of Pseudomonas sp. strain WDL5 needs to be further elucidated. The degradation of linuron can thus be performed by a single isolate, Variovorax sp. strain WDL1, but is stimulated by a synergistic interaction with the other strains isolated from the same linuron-degrading culture.

Present address: Flemish Institute for Technological Research (Vito), 2400 Mol, Belgium.

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