Biodegradation of topramezone by a Trichoderma isolate in soil.

Topramezone, a pyrazolone or benzoylpyrazole compound has been introduced in many countries as a post-emergence HPPD inhibiting herbicide to control annual grass and broadleaf weeds in maize. Topramezone is highly persistent and has high mobility in soil risking the ground water. The impact of the herbicide in the agricultural environment is not much known. An investigation on the interaction between beneficial microorganisms and topramezone in soil was attempted to reveal the scope of its bioremediation. One microbial strain capable of transforming topramezone was isolated from contaminated soils and characterized as Trichoderma sp. It survived in the minimal broth having topramezone at the level of 500 mg per liter of media. In sterilized soil spiked with herbicide, Trichoderma degraded 90% of the applied topramezone within 30 days of incubation. The herbicide degraded through various biochemical reactions, viz. decarbonylation, demethylation, alkyl hydroxylation, methoxylation, hetero ring hydroxylation, oxidation of ketone double bond, and desulfonylation. Metabolites formed in the soil and media within 30 days after incubation were identified by analyzing them in liquid chromatography-mass spectroscopy. Major metabolites were: 3-(4,5-dihydro-1,2-oxazol-3-yl)-4-mesylphenyl](5-hydroxy-1-methyl-pyrazol-4-yl)methanone; [3-(4,5-dihydro-1,2-oxazol-3-yl)-4-hydroxy-o-tolyl](5-hydroxy-1-methyl-pyrazol-4-yl)methanone; [3-(4,5-dihydro-1,2-oxazol-3-yl)-2-hydroxymethyl-4-hydroxyphenyl](5-hydroxy-1-methyl-pyrazol-4-yl)methanone; [3-(4,5-dihydro-1,2-oxazol-3-yl)-4-hydroxyphenyl](5-hydroxy-1-methyl-pyrazol-4-yl)methanone; 2-(4,5-dihydro-1,2-isoxazol-3-yl)-4-hydroxytoluene; 1-hydroxymethyl-5-hydroxy-4-pyrazolecarboxylic acid; 1-methoxy-4-hydroxy-4,5-dihydroisoxazole; 1-methoxy-4,5-dihydro-isoxazole. These observations strongly imply the presence of a substrate recognition mechanism and a corresponding metabolic response system in the Trichoderma sp. to effectively degrade topramezone in the environment.