[Arsenic metabolism in purple nonsulfur bacteria]

To elucidate the arsenic metabolic pathway of purple nonsulfur bacteria (PNSB).

We investigated the distribution within their genomes, organization, composition, arrangement, core genes and coding proteins of arsenic gene clusters found in complete genome from 17 strains of PNSB by comparing the genomes analysis, and studied the arsenic metabolism in 3 members of PNSB under anaerobic conditions by UV-Vis and HPLC-ICP-MS.

Arsenate reduction and arsenite methylation pathways mediated by ars operon are the dominating arsenic metabolic processes. The arsenic gene clusters differ vastly in composition and arrangement. Some members of PNSB evolved two independently families of arsenate reduction genes (arsC). The cells of Rhodopseudomonas palustris CQV97, Rhodobacter azotoformans 134K20 and Rhodobacter capsulatus XJ-1 could reduce As (V) to As (III), whereas As (III) could not be transformed back to As (V). Higher concentration phosphate competitively inhibited arsenate toxicity to cells.

Our investigations shed light on the evolution and functional implications in arsenic gene clusters of PNSB, and support the notion that arsenate reduction and arsenite methylation appears to be the dominant process in PNSB.