Bacterial Chemotaxis to Atrazine and Relateds-Triazines

Abstract

Pseudomonas sp. strain ADP utilizes the human-made s-triazine herbicide atrazine as the sole nitrogen source. The results reported here demonstrate that atrazine and the atrazine degradation intermediates N-isopropylammelide and cyanuric acid are chemoattractants for strain ADP. In addition, the nonmetabolized s-triazine ametryn was also an attractant. The chemotactic response to these s-triazines was not specifically induced during growth with atrazine, and atrazine metabolism was not required for the chemotactic response. A cured variant of strain ADP (ADP M13-2) was attracted to s-triazines, indicating that the atrazine catabolic plasmid pADP-1 is not necessary for the chemotactic response and that atrazine degradation and chemotaxis are not genetically linked. These results indicate that atrazine and related s-triazines are detected by one or more chromosomally encoded chemoreceptors in Pseudomonas sp. strain ADP. We demonstrated that Escherichia coli is attracted to the s-triazine compounds N-isopropylammelide and cyanuric acid, and an E. coli mutant lacking Tap (the pyrimidine chemoreceptor) was unable to respond to s-triazines. These data indicate that pyrimidines and triazines are detected by the same chemoreceptor (Tap) in E. coli. We showed that Pseudomonas sp. strain ADP is attracted to pyrimidines, which are the naturally occurring structures closest to triazines, and propose that chemotaxis toward s-triazines may be due to fortuitous recognition by a pyrimidine chemoreceptor in Pseudomonas sp. strain ADP. In competition assays, the presence of atrazine inhibited chemotaxis of Pseudomonas sp. strain ADP to cytosine, and cytosine inhibited chemotaxis to atrazine, suggesting that pyrimidines and s-triazines are detected by the same chemoreceptor.Atrazine [2-chloro-4-(N-ethylamino)-6-(N-isopropylamino)-1,3,5-s-triazine] is a human-made herbicide that is used worldwide to control broadleaf and grassy weeds. As one of the most heavily used herbicides in the United States, atrazine can be present in parts per million in agricultural runoffs (3), which exceeds the U.S. Environmental Protection Agency's maximum allowable contaminant level of 3 ppb in ground and surface waters (13). Atrazine is persistent in soil (34) and was once considered nontoxic to animals. However, recent studies have shown that atrazine causes sexual abnormalities in frogs (21,22,50), reduced testosterone production in rats (53), and elevated levels of prostate cancer in workers at an atrazinemanufacturing factory (45). These studies suggest that there is cause for concern about atrazine residues in soil, groundwater, and surface waters.Several bacterial strains capable of mineralizing atrazine have been isolated (4,27,41,49,51,52,58). The best-studied atrazinedegrading strain, Pseudomonas sp. strain ADP (atrazine degrading pseudomonad), was isolated from an atrazine spill site in Minnesota (27). Strain ADP utilizes atrazine as a sole nitrogen source and mineralizes it in the process (27). The pathway of atrazine degradation in strain ...

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