Arsenic-related microorganisms in groundwater: a review on distribution, metabolic activities and potential use in arsenic removal processes

Groundwater plays a central role in the hydrological cycle and represents the utmost natural resource for human consumption and activities on a global scale. Therefore, any source of contamination of either geogenic or anthropogenic origin may provide a serious environmental health threat. Within the long list of organic and inorganic groundwater contaminants, arsenic, a toxic element retrieved in air, soils, rocks, waters and organisms, can occur at high concentrations in aquifers representing an issue of worldwide concern. Over the past years, research efforts aimed to elucidate the microorganisms and mechanisms involved in the biogeochemical cycling of this element. An emerging challenge is to identify and exploit microbial metabolic potentialities for arsenic-contaminated water treatment. The objective of this review is to outline the existing knowledge about ecology, biochemistry and genomics of arsenic-related microorganisms, with particular reference to their distribution and their capabilities to oxidize As(III) in groundwater. Moreover, a broad evaluation of the application potentialities of microbiological processes suitable for treatment strategies of arsenic-contaminated groundwater is provided.