Transformation of roxarsone by Enterobacter sp. CZ-1 isolated from an arsenic-contaminated paddy soil

Roxarsone [Rox(V)] is widely used as a feed additive in poultry industries. This arsenic-containing compound may be degraded by microbes to release toxic inorganic arsenic in the environment. To date, most of the studies of microbial mediated Rox(V) degradation have focused on anaerobic microorganisms. Here, we isolated a pure cultured aerobic Rox(V)-degrading bacterial strain, CZ-1, from an arsenic-contaminated paddy soil in China. On the basis of 16S rRNA gene sequence, strain CZ-1 was classified as a member of genus Enterobacter. This strain could efficiently degrade Rox(V), converting all of 10 μM Rox(V) within 24 h in liquid culture. Four metabolites including n-acetyl-4-hydroxy-m-arsanilic acid (N-AHPAA[V]), 3-amino-4-hydroxyphenylarsonic acid (3-AHPAA[V]), arsenite (As[III]) and an unknown arsenic compound were detected and identified by HPLC-ICP-MS and HPLC-LC-MS. N-AHPAA(V) was the main product, likely to be formed from acetylation of 3-AHPAA(V). Based on these results, a novel degradation pathway of Rox(V) by Enterobacter. sp CZ-1 is proposed.