Degradation of Four Herbicides by Bacteria Degrading Pendimethalin

Abstract

The current studies were carried out to analyse the degradation of pendimethalin in soil and that of herbicides such as trifluralin, nitralin and alachlor by several bacterial strains P-1, P-3 and P-e which are able to degrade pendimethalin.
The degradation of pendimethalin was investigated by using the following soils; sterile soil, non-sterile soil and sterile soil with a suspension of P-3 strain. It was demonstrated that pendimethalin was readily degraded in the non-sterile soil and the amount of residue decreased by half 55 days after incubation, whereas the herbicide in sterile soil was not degraded even after 62 days, and 90% of the initial amount could be recovered. In sterile soil to which the P-3 strain had been added, the degradation rapidly progressed until 20 days, and thereafter stopped (Fig 2).
Trifluralin and nitralin were markedly degraded by all the three strains in mineral salt medium, whereas alachlor was slightly degraded by the P-e strain alone (Table 1). The three metabolic products from trifluralin detected by GC analysis was found to correspond to two products formed by the reduction of one or two nitro-groups of trifluralin and a compound having a benzimidazol structure (Fig. 3) based on GC-MS analysis. Major metabolites of nitralin were also detected as two products formed by the reduction of nitro-groups.