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 atzD, were not

detected. Potential intermediates of atrazine catabolic route such as hydroxyatrazine, desethylatrazine,

and desisopropylatrazine, and desisopropylatrazine were utilized as sources of carbon and energy,

while desisoprophl 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.