AS-101

Microorganisms play a critical role in the biotransformation of arsenic and the form which it exists in the environment. In this study, a methyl parathion-degrading bacterium Caballeronia jiangsuensis, isolated from an abandoned pesticide manufacturing plant, was used to analyze arsenic accumulation and transformation. The accumulation of trivalent organoarsenic compounds in C. jiangsuensis occurred to a greater extent than that of their pentavalent counterparts. The chromosome of C. jiangsuensis contains an arsenic gene island whose GC content is significantly lower than that of the genome, suggesting that the island was acquired via horizontal gene transfer. There was approximately 90 %-99 % similarity between the proteins encoded by the gene island and the corresponding sequence of the plasmid pkk5 from Burkholderia sp. KK1. The biotransformation of different arsenic species by C. jiangsuensis was subsequently analyzed. The results revealed that monomethylarsenic acid (MAs(V)) was rapidly demethylated to arsenate with very small amounts of intermediate monomethylarsonous acid (MAs(III)), whereas MAs(III) was largely oxidized to MAs(V) despite the occurrence of the gene arsI probably responsible for aerobic demethylation of MAs(III) in C. jiangsuensis. In addition, dimethylarsenic acid was partly demethylated to arsenate. Horizontal gene transfer of ars operon from a plasmid to other bacteria represents an adaptation to a specific environment. This study provides a new perspective for understanding arsenic biogeochemical cycling.