Evaluation of the atzB gene as a functional marker for the simazine-degrading potential of an agricultural soil

The occurrence of natural simazine-degrading bacteria could be an important limiting factor to the use of the herbicide in those agricultural soils with a wide history of herbicide applications. In this work the potential of an agricultural soil to degrade simazine and the effect of the addition of urea was assayed in both fertilised and unfertilised soil microcosms. A culture-independent approach based on the fluorescence in situ hybridisation (FISH) technique, using a specific oligonucleotide probe (AtzB1), was applied to detect simazine-degrading bacteria in the soil microcosms. The presence of the atzABC genes in the agricultural soil was confirmed by PCR from soil-extracted DNA. The percentage of AtzB1 probe-target cells in the urea-untreated soil was higher than in the urea-treated one. Moreover, the greatest percentage of AtzB1 probe-target cells in the urea-untreated soil was accompanied by a greater degradation rate, compared to the urea-fertilised one. Our results indicate that the proposed approach was sensitive enough to detect changes in the natural simazine degradation capacity of the soil after fertilisation practices, which typically involve a nitrogen increase.