Sunday, July 24, 2011
Grand Ballroom, 5th fl (Sheraton New Orleans)
Arsenic is one of the most wide-spread environmental carcinogens and has created devastating human health problems world-wide, yet little is known about the mechanisms of biotransformation in contaminated regions. Methylarsonic acid [MAs(V)] has been extensively utilized as an herbicide. Once released into the environment, the pentavalent methylarsenical is largely demethylated to more toxic inorganic arsenic, which causes environmental problems. To understand the process of demethylation of methylarsenicals, MAs(V) contaminate soil samples were studied. Several soil extracts were found to demethylate MAs(V) to inorganic arsenite [As(III)]. No single organism capable of MAs(V) demethylation was isolated, but several formed a microbial community could carry out this process. One bacterial isolate capable of reducing MAs(V) to MAs(III) but not of demethylating to As(III) was isolated. Other isolates were capable of demethylating MAs(III) to As(III) but not of reducing MAs(V). A mixed culture could carry out reduction and demethylation, demonstrating that it is a two step process. Analysis of 16S ribosomal DNA (rDNA) sequences revealed that the MAs(V)-reducing isolate is a Burkholderia species, and MAs(III)-demethylating isolates are Streptomyces and Bacillus species. This is the first report of a novel pathway of degradation of a methylarsenical herbicide by sequential reduction and demethylation in a microbial soil community, which we propose plays a significant role in the arsenic biogeocycle. The identification of the genes for MMA(V) reductases from Burkholderia sp. and MMA(III) demethylases from Streptomyces sp. And Bucillus sp. is currently in progress. (Supported by NIH grant R37 GM55425)