Simazine treatment history determines a significant herbicide degradation potential in soils that is not improved by bioaugmentation with Pseudomonas sp. ADP

Aims: To study biological removal of the herbicide simazine in soils with different history of herbicide treatment and to test bioaugmentation with a simazine-degrading bacterial strain. Methods and Results: Simazine removal was studied in microcosms prepared with soils that had been differentially exposed to this herbicide. Simazine removal was much higher in previously exposed soils than in unexposed ones. Terminal restriction fragment length polymorphism analysis and multivariate analysis showed that soils previously exposed to simazine contained bacterial communities that were significantly impacted by simazine but also had an increased resilience. The biodegradation potential was also related to the presence of high levels of the atz-like gene sequences involved in simazine degradation. Bioaugmentation with Pseudomonas sp. ADP resulted in an increased initial rate of simazine removal, but this strain scarcely survived. After 28 days, residual simazine removals were the same in bioaugmented and not bioaugmented microcosms. Conclusions: In soils with a history of simazine treatment bacterial communities were able to overcome subsequent impacts with the herbicide. The success of bioaugmentation was limited by the low survival of the introduced strain. Significance and Impact of the Study: Conclusions from this work provided insights on simazine biodegradation potential of soils and the convenience of bioaugmentation.