Simazine treatment history determines a significant herbicide degradation potential in soils

3 that is not improved by bioaugmentation with Pseudomonas sp. ADP. ABSTRACT 1 2 AIMS: To study biological removal of the herbicide simazine in soils with different history of 3 herbicide treatment and to test bioaugmentation with a simazine degrading bacterial strain. 5 soils that had been differentially exposed to this herbicide. Simazine removal was much 6 higher in previously exposed soils than in unexposed ones. Terminal restriction fragment 7 length polymorphism analysis and multivariate analysis showed that soils previously 8 exposed to simazine contained bacterial communities that were significantly impacted by 9 simazine but also had an increased resilience. The biodegradation potential was also 10 related to the presence of high levels of the atz-like gene sequences involved in simazine 11 degradation. Bioaugmentation with Pseudomonas sp. ADP resulted in an increased initial 12 rate of simazine removal, but this strain scarcely survived. After 28 days, residual simazine 13 removals were the same in bioaugmented and not bioaugmented microcosms.