Molecular analysis of atrazine-degrading bacteria and catabolic genes in the water column and sediment of a created wetland in an agricultural/urban watershed

• Atrazine biodegradation was examined in a constructed riverine wetland.
• Water column and sediment samples were screened for bacteria and catabolic genes.
• Atrazine laden Bio–Sep beads were used to trap atrazine-degrading bacteria.
• Biomineralization of [U-ring-14C]-atrazine by retrieved beads was negligible.
• Nucleotide sequences of16S rRNA, atz and trz genes were analyzed.

Atrazine-mineralizing bacteria were enriched from water and sediment samples from a constructed flow-through wetland that received water from a river with an agricultural watershed. Bio–Sep beads laden with atrazine were submerged in the wetland sediment and water column in an attempt to sorb atrazine-metabolizing microbes on beads. Biometer experiments with in-situ incubated beads did not detect 14CO2 formation from 14C-atrazine. HPLC analysis was used to rank atrazine biodegradation by enrichment cultures from wetland samples. Analysis of the 16S rRNA gene sequences of 60 clones from aerobic enrichment cultures revealed the predominance of the genera Acidovorax (33%), Ralstonia (22%), Azorhizobium (12%), and Xanthobacter (12%) with sequence match ≥0.90 in wetland samples. Similar analysis of 12 clones from anaerobic enrichment cultures revealed the predominance of the genera Hydrogenophaga (42%) and Rhizobium (25%). Pure culture isolates (n = 18) were primarily Arthrobacter spp. (89%) at sequence match ≥0.97. Pure cultures were screened qualitatively for the presence of 8 catabolic genes associated with known pathways of atrazine biodegradation. None of the cultures had all Atz pathway genes and none contained atzD and trzD genes. AtzC was found in all isolates. The data indicate that the diversity of atrazine degraders was comparable to findings in agricultural soil studies, with the notable cluster of Arthrobacter spp. which may be favored by the culture conditions used for isolation.