A comparison of three atrazine-degrading bacteria for soil bioremediation

The ability of three atrazine-degrading bacteria, Pseudomonas sp. strain AD P, a Pseudaminobacter sp., and a Nocardioides sp., to degrade and mineraliz e this herbicide in a loam soil was evaluated in laboratory microcosms. The se bacteria all hydrolytically dechlorinate atrazine, and degrade atrazine in pure culture with comparable specific activities. The Pseudaminobacter a nd Nocardioides can utilize atrazine as sole carbon and nitrogen source, wh ereas the Pseudomonas can utilize the compound only as a nitrogen source. T he Pseudomonas and Pseudaminobacter mineralize the compound; the end produc t of atrazine metabolism by the Nocardioides is N-ethylammelide. At inoculu m densities of 10(5) cells/g soil, only the Pseudaminobacter and Nocardioid es accelerated atrazine dissipation. The Pseudaminobacter mineralized atraz ine rapidly and without a lag, whereas atrazine was mineralized in the Noca rdioides-inoculated soil but only after a lag of several days. The Pseudami nobacter remained viable longer than did the Pseudomonas in soil. PCR analy sis of recovered bacteria indicated that the genes atzA (atrazine chlorohyd rolase) and atzB (hydroxyatrazine ethylaminohydrolase) were less stable in the Pseudaminobacter than the Pseudomonas. In summary, this study has revea led important differences in the ability of atrazine-hydrolyzing bacteria t o degrade this compound in soil, and suggests that the ability to utilize a trazine as a carbon source is important to establish "enhanced degradation" by ecologically meaningful inoculum densities.