Abstract
Due to the toxicity of this metalloid, arsenic contamination currently represents one of the most severe threats for the environment and public health in many countries worldwide with millions of people chronically exposed, mainly in Southeast Asia. Redox transformations strongly impact arsenic environmental fate, since its solubility bioavailability and toxicity depend on its speciation. Microorganisms play a key role in these transformations with the presence in the environment of many microorganisms able to metabolize this toxic element using detoxification or energy conservation reactions based on redox reactions, methylation, or demethylation. This chapter highlights the current knowledge concerning the ecology, physiology, and genomics of these microorganisms and provides an update on the development of processes removing arsenic present in soil and water based on microbial transformations.