Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/1998
Publication Date: N/A
Interpretive Summary: Many agricultural dealerships across the country have soil contaminated with pesticides. At thousands of these sites, contamination is severe enough to warrant cleanup. Bioremediation is a potential low-cost strategy for cleanup, but knowledge of pesticide bioremediation is limited. This research was part of an integrated program to develop in situ bioremediation approaches for pesticides, including atrazine. An atrazine-degrading microorganism, Agrobacterium radiobacter, was isolated from soil. Although the organism uses the nitrogen in atrazine as a nutrient, nitrogen from other sources does not stop degradation. Additional sucrose increases the bacterium's activity in liquid culture. The bacterium is also capable of degrading four other triazine herbicides. We added this bacterium to soil contaminated with atrazine from two agricultural dealerships. In one soil, the bacterium removed 45 to 80% of the atrazine. Adding sucrose to the soil increased degradation in some experiments, but not in others. The second soil contained a population of native microorganisms that also degraded atrazine; inoculation did not increase the rate of degradation. If survival of this microorganism can be increased, it will be potentially useful in bioremediating soils containing high concentrations of triazine herbicides.
Technical Abstract: We examined the ability of a soil bacterium, Agrobacterium radiobacter strain J14a, to degrade the herbicide atrazine under a variety of cultural conditions and used this bacterium to increase the biodegradation of atrazine in soils from agricultural chemical distribution sites. J14a cells grown in N-free media with citrate and sucrose as C sources mineralized 94% of 50 ug ml**-1 [**14C-UL-ring]-atrazine in 72 h with a concurrent increase in the population size from 7.9x10**5 to 5x10**7 cells ml**-1. Under these conditions cells mineralized the [**14C-ethyl]-atrazine and incorporated approximately 30% of the **14C into J14a biomass. Cells grown in medium without additional C and N sources degraded atrazine, but the cell numbers did not increase. Metabolites produced by J14a during atrazine degradation include hydroxyatrazine (HA), deethylatrazine (DEA), and deethyl-hydroxyatrazine (DEHA). Addition of 10**5 J14a cells g**-1 into soil with a low indigenous population of atrazine degraders treated with 50 and 200 ug atrazine g**-1 soil resulted in two to five times higher mineralization than the non-inoculated soil. Sucrose addition did not result in significantly faster mineralization rates or shorten degradation lag times. However, J14a introduction (10**5 cells g**-1) into another soil with a larger indigenous atrazine-mineralizing population reduced atrazine degradation lag times below those in non-inoculated treatments but did not generally increase total atrazine mineralization.