Nitrogen-dependent induction of atrazine degradation pathway in Pseudomonas sp. strain AKN5

Soil isolate Pseudomonas sp. strain AKN5 degrades atrazine as the sole source of nitrogen. The strain showed expeditious growth on medium containing citrate as the carbon source and ammonium chloride as the nitrogen source as compared to citrate plus atrazine or cyanuric acid. Biochemical and nitrogen-source-dependent enzyme induction studies revealed that atrazine is metabolized through hydrolytic pathway and has two segments: the upper segment converts atrazine into cyanuric acid while the lower segment metabolizes cyanuric acid to CO2 and ammonia. Bioinformatics and co-transcriptional analyses suggest that atzA, atzB and atzC were transcribed as three independent transcripts while atzDEF were found to be transcribed as a single polycistronic mRNA indicating operonic arrangement. Transcriptional analysis showed inducible expression of atzA/B/C/DEF from atrazine grown cells while cyanuric acid grown cells showed significantly higher expression of atzDEF. Interestingly, growth profiles and enzyme activity measurements suggests that strain utilizes a simple nitrogen source (ammonium chloride) over the complex (atrazine or cyanuric acid) when grown on dual nitrogen source. These results suggest that atrazine degradation genes were up-regulated in the presence of atrazine but repressed in the presence of simple nitrogen source like ammonium chloride.