Genome analysis of atrazine degradation in Arthrobacter aurescens strain TC1.

摘要

The gram-positive bacterium Arthrobacter aurescens strain TC1 degrades atrazine to cyanuric acid via three enzymatic steps encoded by the trzN, atzB and atzC genes. A BAC library approach localized all three atrazine catabolic genes to a single 161,264 nucleotide region of the A. aurescens genome, which was completely sequenced. Physical, genetic, and sequence data strongly suggests that these catabolic genes are located on a 380 kb plasmid, and localized within two clusters in the A. aurescens genome. The trzN gene was located 129 kb and 122.5 kb from the atzB and atzC genes, respectively, and the latter two genes were 5.2 kb apart. The TrzN homolog from A. aurescens shared 99% amino acid identity with TrzN from Nocardioides sp. strain C190, but genes surrounding trzN were different in the two strains. The BAC sequence was composed of three clusters of genes, cluster I had significant identity to plasmid pADP-1 (surrounding the atzB and atzC genes) from Pseudomonas ADP, cluster II (upstream of trzN) consisted of a region having high similarity to plasmid pAO1 from Arthrobacter nicotinovorans, and cluster III, the remainder of the ORFs, comprised genes identified in the gram-positive bacteria, Streptomyces, Corynebacter, and Rhodococcus . The atzB, and atzC genes were flanked by different insertion elements or transposases, and the latter gene had vastly different mole % G+C than trzN, suggesting independent acquisition of these genes by A. aurescens TC1. Moreover, since atzB and atzC were organized differently and divergently transcribed in Arthrobacter TC1 and Pseudomonas ADP, these results suggest that the atrazine degradation pathway in Arthrobacter aurescens strain TC1 was acquired by independent horizontal gene transfer and transposition events. The stability of TrzN, AtzB and AtzC inside A. aurescens strain TC1 cell was investigated using glutaraldehyde and spray drying. While both of these preservation methods allowed retention of the activities of all three enzymes, untreated A. aurescens strain TC1 cells suspended in 30% glycerol had 73%, 97% and 92% of TrzN, AtzB and AtzC activity, respectively, after 4 months.