Degradation of Pendimethalin by Bacteria Isolated from Soil

Abstract

This paper describes the degradation of the herbicide, pendimethalin [N-(1-ethylpropyl)-2, 6-dinitro-3, 4-xylidine] by bacteria isolated from farmland soil previously treated with it, and the identification of several metabolites produced by bacterial inoculation.
Among ten bacterial strains isolated from the soil, three strains, P-1, P-3 and P-e showed a high ability to degrade pendimethalin in mineral salt medium supplemented with 5ppm of the chemical.
The residue level of pendimethalin 40 days after inoculation was 35.1, 9.8 and 12.6% in the medium containing the P-1, P-3 and P-e strains, respectively (Table 1 and Fig. 1).
Four degradation products in the reaction mixture were detected by GC and GC-MS analysis. Among these products, the major metabolite (metabolite 1, m/z 251) was assumed to be a reduced product of a nitro-group of pendimethalin. The other three metabolites were considered to be a benzimidazole (metabolite 2, m/z 261) and compounds produced by the hydroxylation of methyl or propyl groups (metabolites 3, 4, m/z 297) (Fig. 3). Metabolites 1 and 2 were common products of all three bacterial strains, whereas metabolites 3 and 4 were detectable in the medium with the P-3 strain only (Fig. 4).
Moreover, it was assumed that the P-1 and P-3 strains belong to the genus Bacillus and the P-e strain to the genus Alcaligenes based on the main bacteriological properties (Table 2).