Quantification of the atrazine-degrading Pseudomonas sp. strain ADP in aquifer sediment by quantitative competitive polymerase chain reaction.

The widely used herbicide atrazine and some of its degradation products are among the most commonly found xenobiotics in groundwater in Europe as well as in the USA. The bacterium Pseudomonas sp. strain ADP (P. ADP) possesses genes encoding atrazine mineralization on the self-transmissible plasmid pADP-1. In the present study, this ability of the strain to mineralize atrazine in aquifer sediment under both aerobic and denitrifying conditions at 10 degrees C was studied. P. ADP was able to mineralize more than 50% of 2.8 muM atrazine within 14 days under both growth conditions. Counts of degraders as colony forming units (CFU) on atrazine plates and counts of atzA gene copies as determined by quantitative competitive polymerase chain reaction (cPCR) were performed. The atzA gene encodes the enzyme which catalyzes the first step of atrazine mineralization by the strain. Quantification of the atzA gene gave rise to higher numbers than did counts of CFU. High nitrate concentrations inhibited atrazine mineralization and culturability on agar plates, but atzA copy numbers remained stable throughout the experiment. The results show a potential for bioaugmentation using P. ADP at both aerobic and denitrifying conditions and the use of cPCR as a tool for monitoring the bacteria independent of culturability.