Evidence of atrazine mineralization in a soil from the Nile Delta: Isolation of Arthrobacter sp. TES6, an atrazine-degrading strain

Abstract

The s-triazine herbicide atrazine was rapidly mineralized (i.e., about 60% of 14C-ring-labelled atrazine released as 14CO 2 within 21 days) by an agricultural soil from the Nile Delta (Egypt) that had been cropped with corn and periodically treated with this herbicide. Seven strains able to degrade atrazine were isolated by enrichment cultures of this soil. DNA fingerprint and phylogenetic studies based on 16S rRNA analysis showed that the seven strains were identical and belonged to the phylogeny of the genus Arthrobacter (99% similarity with Arthrobacter sp. AD38, EU710554). One strain, designated Arthrobacter sp. strain TES6, degraded atrazine and mineralized the 14C-chain-labelled atrazine. However, it was unable to mineralize the 14C-ring-labelled atrazine. Atrazine biodegradation ended in a metabolite that co-eluted with cyanuric acid in HPLC. This was consistent with its atrazine-degrading genetic potential, shown to be dependent on the trzN, atzB, and atzC gene combination. Southern blot analysis revealed that the three genes were located on a large plasmid of about 175 kb and clustered on a 22-kb SmaI fragment. These results reveal for the first time the adaptation of a North African agricultural soil to atrazine mineralization and raise interesting questions about the pandemic dispersion of the trzN, atzBC genes among atrazine-degrading bacteria worldwide.