Identification of an arsenic resistance mechanism in rhizobial strains

Abstract

Arsenic (As) is a very toxic metalloid to a great number of organisms. It is one of the most important global environmental pollutants. To resist the arsenate invasion, some microorganisms have developed or acquired genes that permit the cell to neutralize the toxic effects of arsenic through the exclusion of arsenic from the cells. In this work, two arsenic resistance genes, arsA and arsC, were identified in three strains of Rhizobium isolated from nodules of legumes that grew in contaminated soils with effluents from the chemical and fertilizer industry containing heavy-metals, in the industrial area of Estarreja, Portugal. The arsC gene was identified in strains of Sinorhizobium loti [DQ398936], Rhizobium leguminosarum [DQ398938] and Mesorhizobium loti [DQ398939]. This is the first time that arsenic resistance genes, namely arsC, have been identified in Rhizobium leguminosarum strains. The search for the arsA gene revealed that not all the strains with the arsenate reductase gene had a positive result for ArsA, the ATPase for the arsenite-translocating system. Only in Mesorhizobium loti was the arsA gene amplified [DQ398940]. The presence of an arsenate reductase in these strains and the identification of the arsA gene in Mesorhizobium loti, confirm the presence of an ars operon and consequently arsenate resistance.