Survival and activity of an atrazine-mineralizing bacterial consortium in rhizosphere soil

Plant rhizosphere effects on atrazine degradation were examined in soil inoculated with an atrazine-mineralizing bacterial consortium. The consortium, consisting of three bacterial species, was isolated from an agricultural soil having previous long-term exposure to the herbicide. Atrazine mineralization and metabolite formation were monitored by measuring (CO2)-C-14 evolution from microcosms amended with radiolabeled atrazine and by HPLC of soil extracts. In noninoculated soil, ca. 11% of C-14-chain-labeled atrazine was N-dealkylated, while only 2.4% of the ring-labeled atrazine was mineralized after 5 weeks. Corn plants had no effect on atrazine mineralization or ethyl-side-chain N-dealkylation in noninoculated soils, but the formation of hydroxyatrazine was significantly enhanced in planted soil. Growth of corn in sterilized soil suggested that hydroxyatrazine formation was caused by plant metabolism of atrazine. introduction of the atrazine-mineralizing consortium into the soil significantly increased the rate of atrazine mineralization in comparison to noninoculated soil. After 4 weeks, 71% of the atrazine was mineralized in nonplanted soil, whereas 84% of the atrazine was mineralized in soil with corn plants. There was no significant difference in the rate of atrazine mineralization by the consortium in nonplanted and planted soil. However, atrazine-mineralizing populations at the end of the incubation were higher in the planted soil, which contained 8.1 x 10(4) degraders g(-1) of soil versus 2.7 x 10(3) degraders g(-1) in soil without plants. The results demonstrated that bioaugmentation with the atrazine-mineralizing consortium greatly enhanced the rate of atrazine mineralization. Long-term survival of the consortium and degradation of atrazine to hydroxyatrazine were both enhanced in rhizosphere soil, but corn seedlings had no significant effect on the rate of atrazine mineralization, either by the indigenous microflora or in soil inoculated with atrazine-mineralizing bacteria.