Arthrobacter aurescens strain TC1 metabolizes atrazine to cyanuric acid via TrzN, AtzB, and AtzC. The complete sequence of a 160-kb bacterial artificial chromosome clone indicated that trzN, atzB, and atzC are linked on the A. aurescens genome. TrzN, AtzB, and AtzC were shown to be functional in Escherichia coli. Hybridization studies localized trzN, atzB, and atzC to a 380-kb plasmid in A. aurescens strain TC1.The complete nucleotide sequences of over 100 bacterial plasmids are now available, but most of these plasmids are relatively small and of interest primarily in microbial pathogenesis (for example, in the context of antibiotic resistance or toxin production). By contrast, only a limited number of large catabolic plasmids or catabolic islands on chromosomes have been sequenced. Examples include plasmids pNL1 from Sphingomonas aromaticivorans strain F199 (23), pAO1 from Arthrobacter nicotinovorans (11), pACR1 from Pseudomonas resinovorans strain CA10 (13), the TOL plasmid pWW0 from Pseudomonas putida (9), pBD2 from Rhodococcus erythropolis BD2 (31), pADP-1 from Pseudomonas sp. strain ADP (16), and the 105-kb catabolic island from Pseudomonas sp. strain B13 (28). Large catabolic plasmids can be difficult to isolate for sequencing. Thus, to facilitate widespread sequencing of large catabolic gene regions, more innovative strategies are needed. For example, plasmids have been identified via whole-genome shotgun sequencing of Deinococcus radiodurans (41) and Enterococcus faecalis (19).A wide variety of bacteria degrading the herbicide atrazine have been reported (2,14,21,22,32,36,37,43), and in all cases examined except one (3) the genes involved are located on plasmids (5,25,36,39). In Pseudomonas sp. strain ADP (14), the six atrazine-catabolic genes (atzA, atzB, atzC, and atzDEF) have been localized to plasmid pADP-1, from which the complete nucleotide sequence is now available (16). The atzA, atzB, and atzC genes have also been localized to different-sized plasmids in the gram-negative bacteria Chelatobacter heintzii, Stenotrophomonas maltophilia, and Pseudaminobacter spp., and hybridization analyses indicate that the atzB and atzC genes reside on a 117-kb plasmid in the gram-positive bacterium Arthrobacter crystallopoietes (25,36). The presence of nearly identical atrazine genes in Agrobacterium, Clavibacter, Rhizobium, Pseudomonas, Alcaligenes, and Ralstonia strains (2,5,22,24,33,39) further suggests that horizontal gene transfer is involved in the dissemination of atrazine-catabolic genes.Some differences have been observed in the gene content of the gram-positive atrazine-degrading bacteria Nocardioides sp. strains C190, SP12, and C157, Arthrobacter crystallopoietes, and Arthrobacter sp. strain AD1 (3,21,24,25,32,37). Nocardioides sp. strain C190 (37) does not contain atzA, atzB, or atzC, and atrazine degradation is initiated by the product of the trzN gene, which has been cloned and sequenced previously (17). A. crystallopoietes was shown to contain trzN, atzB, and atzC (25).The isolation and characteri...

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International audienc

The microbial community structure in Thailand soils contaminated with low and high levels of arsenic was determined by denaturing gradient gel electrophoresis. Band pattern analysis indicated that the bacterial community was not significantly different in the two soils. Phylogenetic analysis obtained by excising and sequencing six bands indicated that the soils were dominated by Arthrobacter koreensis and β-Proteobacteria. Two hundred and sixty-two bacterial isolates were obtained from arsenic-contaminated soils. The majority of the As-resistant isolates were Gramnegative bacteria. MIC studies indicated that all of the tested bacteria had greater resistance to arsenate than arsenite. Some strains were capable of growing in medium containing up to 1,500 mg/l arsenite and arsenate. Correlations analysis of resistance patterns of arsenite resistance indicated that the isolated bacteria could be categorized into 13 groups, with a maximum similarity value of 100%. All strains were also evaluated for resistance to eight antibiotics. The antibiotic resistance patterns divided the strains into 100 unique groups, indicating that the strains were very diverse. Isolates from each antibiotic resistance group were characterized in more detail by using the repetitive extragenic palindromic-PCR (rep-PCR) DNA fingerprinting technique with ERIC primers. The PCR products were analyzed by agarose gel electrophoresis. The genetic relatedness of 100 bacterial fingerprints, determined by using the Pearson product-moment similarity coefficient, showed that the isolates could be divided into four clusters, with similarity values ranging from 5-99%. Although many isolates were genetically diverse, others were clonal in nature. Additionally, the arsenic-resistant isolates were examined for the presence of arsenic resistance (ars) genes by using PCR, and 30% of the isolates were found to carry an arsenate reductase encoded by the arsC gene.

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In this study we examined the influence of silver nanoparticles (SNP) on the bacterial community and microbial processes in two soils from Thailand, a Ayutthaya (Ay) and Kamphaengsaen soil series (Ks). Results of this analysis revealed that SNP did not affect to pH, electrical conductivity, cation exchange capacity, and organic matter in both the Ay and Ks series. Automated ribosomal intergenic spacer analysis (ARISA) analysis profiles showed that bacterial community decreased with increasing SNP concentration. Pearson's correlation coefficient and multidimensional scaling analyses indicated that the effects of SNP on the bacterial community structure depended more on soil types than SNP application rates and incubation periods. Additionally, the results showed that SNP application rates affected on amount of CO2 emissions, while SNP application rates had no effect on N mineralization in both soil types. This study is the first investigation of the effects of SNP on bacterial community using ARISA analysis. Our results might be useful to evaluate the risk associated with the applications of SNP for consumer products and agricultural practices.

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