Metabolism of Atrazine in Liquid Cultures and Soil Microcosms by Nocardioides Strains Isolated from a Contaminated Nigerian Agricultural Soil

Abstract

Atrazine-degrading microorganisms designated EAA-3 and EAA-4, belonging to the genus Nocardioides, were obtained from an agricultural soil in Nigeria. The degradation kinetics of the two strains revealed total disappearance of 25 mg l⁻¹ of atrazine in less than 72 h of incubation at the rate of 0.42 mg l⁻¹ h⁻¹ and 0.35 mg l⁻¹ h⁻¹, respectively. Screening for atrazine catabolic genes in these organisms revealed the presence of trzN, atzB, and atzC. Other genes, specifically atzA, atzD, and trzD, were not detected. Potential intermediates of atrazine catabolic route such as hydroxyatrazine, desethylatrazine, and desisopropylatrazine were utilized as sources of carbon and energy, while desisopropyl desethyl-2-hydroxyatrazine and desisopropyl-2-hydroxyatrazine were attacked but in the presence of glucose. A soil microcosm study showed that degradation was faster in microcosms contaminated with 13 mg of atrazine per g⁻¹ of soil compared with 480 mg g⁻¹ of soil. In the former, degradation was 10% higher in the inoculated soil than the non-inoculated control (natural attenuation) over the 28-day study period. Corresponding value obtained for the latter was nearly 70% higher. This study has demonstrated that the bacterial strains isolated enhanced atrazine degradation and the catabolic activities of these strains were not affected with increasing soil atrazine concentration.

Keywords:

• BioSep beads
• catabolic genes
• biodegradation
• soil
• atrazine
• nocardioides

Acknowledgements

This work was supported in part by the United States Department of Agriculture, Cooperative, State, Research, Education, and Extension Service, National Research Initiative, grant number 2004-35107-14884. We are grateful to Dr. S.A. Adebusoye for revising the manuscript. We wish to thank Dr. D. Ghosh, Dr. K. Roy, and Dr. V. Srinivasan for technical support.