Isolation and characterization of efficient isoxaben-transforming Microbacterium sp strains from four European soils.
Nutrient-agar plates containing isoxaben (500 mg litre(-1)) were used to isolate isoxaben-metabolising bacteria from four European soils incubated with the herbicide under laboratory conditions. In flask experiments, inoculation of a basal salts medium containing nitrogen and [phenyl-U-14C]isoxaben with an isolate (B2b) resulted in 33% recovery of the initial radioactivity as [14C]carbon dioxide after 2 weeks. A major metabolite identified by GC-MS and NMR analysis as 3-(1-ethyl-1-methylpropyl)isoxazol-5-ylamine accumulated both in basal salts and nutrient broth media. 2,6-Dimethoxybenzoic acid, a suspected metabolite of isoxaben, was not detected in either liquid media. However, the capability of the B2b isolate to use 2,6-dimethoxybenzoic acid as a source of carbon was demonstrated. Soil inoculation with the B2b strain resulted in an increase in the recovery of [14C] carbon dioxide from both [phenyl-U-14C] and [isoxazole-5-14C]isoxaben. The metabolite identified as 3-(1-ethyl-1-methylpropyl)isoxazole-5-ylamine only accumulated if the soil was autoclaved before inoculation. This metabolite was rapidly mineralized by the microflora of a natural soil without history of isoxaben treatment. Homology patterns of sequenced 16S rDNA between isoxaben-transforming isolates and reference strains showed that the four isolates identified belonged to the genus Microbacterium.
Arrault
Sandra
S
Laboratoire de Microbiologie des Sols, Centre de Microbiologie des Sols et de l'Environment, INRA, BP 86510, 21065 Dijon Cedex, France.
Desaint
Stephane
S
Catroux
Colette
C
Sémon
Etienne
E
Mougin
Christian
C
Fournier
Jean Claude
JC
D001419:Bacteria / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D001549:Benzamides / Q000737:chemistry / Q000378:metabolism*; D001565:Benzoates / Q000737:chemistry / Q000378:metabolism*; D001673:Biodegradation, Environmental; D002250:Carbon Radioisotopes; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics; D005060:Europe; D006540:Herbicides / Q000737:chemistry / Q000378:metabolism*; D062425:Hydroxybenzoate Ethers; D007555:Isoxazoles / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D015394:Molecular Structure; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D012988:Soil Microbiology; D017550:Spectroscopy, Fourier Transform Infrared
C472446:3-(1-ethyl-1-methylpropyl)isoxazol-5-ylamine; D001549:Benzamides; D001565:Benzoates; D002250:Carbon Radioisotopes; D004275:DNA, Ribosomal; D006540:Herbicides; D062425:Hydroxybenzoate Ethers; D007555:Isoxazoles; D012336:RNA, Ribosomal, 16S; C472445:2,6-dimethoxybenzoic acid; C057467:isoxaben