Arsenic, a toxic metalloid is nearly ubiquitous in its distribution in the environment causing major health concern throughout the world. Arsenic resistance in the microbes revealed presence of arsenic-resistance genes clustered in arsenic resistance operon. Evolutionarily the earliest cells may possess the ability to detoxify arsenic present abundantly on primordial earth surface. The presence of arsenic resistance (ars) operon in the microbial genome illustrates that ars genes must be ancient. Primordial high environmental arsenic concentration created the selective pressure that maintained these arsenic resistance genes in present-day organisms as the genetic adaptation. Present-day selective pressure for metalloid resistance also comes from the volcanic activities, mining activities, coal burning and anthropogenic sources. Thus, an understanding of the primordial emergence and selection of the ars operon is fundamental to our
understanding of the arsenic resistance biology
Arsenic, microorganism, ars operon, evolution
