Volatilization of Arsenic from Polluted Soil by <i>Pseudomonas putida</i> Engineered for Expression of the <i>arsM</i> Arsenic(III) S‑Adenosine Methyltransferase Gene

Even though arsenic is one of the most widespread environmental carcinogens, methods of remediation are still limited. In this report we demonstrate that a strain of <i>Pseudomonas putida</i> KT2440 endowed with chromosomal expression of the <i>arsM</i> gene encoding the As­(III) S-adenosylmethionine (SAM) methyltransfase from <i>Rhodopseudomonas palustris</i> to remove arsenic from contaminated soil. We genetically engineered the <i>P. putida</i> KT2440 with stable expression of an <i>arsM-gfp</i> fusion gene (GE <i>P. putida</i>), which was inserted into the bacterial chromosome. GE <i>P. putida</i> showed high arsenic methylation and volatilization activity. When exposed to 25 μM arsenite or arsenate overnight, most inorganic arsenic was methylated to the less toxic methylated arsenicals methylarsenate (MAs­(V)), dimethylarsenate (DMAs­(V)) and trimethylarsine oxide (TMAs­(V)­O). Of total added arsenic, the species were about 62 ± 2.2% DMAs­(V), 25 ± 1.4% MAs­(V) and 10 ± 1.2% TMAs­(V)­O. Volatilized arsenicals were trapped, and the predominant species were dimethylarsine (Me₂AsH) (21 ± 1.0%) and trimethylarsine (TMAs­(III)) (10 ± 1.2%). At later times, more DMAs­(V) and volatile species were produced. Volatilization of Me₂AsH and TMAs­(III) from contaminated soil is thus possible with this genetically engineered bacterium and could be instrumental as an agent for reducing the inorganic arsenic content of soil and agricultural products