Bioremediation potential of soil fungi in arsenic contaminated soils

Microorganisms such as fungi, bacteria and algae have been reported as efficient bioremediators of heavy metals from contaminated areas. Among microorganisms, fungi execute an important role in heavy metal removal from the polluted areas. Fungi possess biochemical and ecological capacities to decrease the risk associated with metals and metalloids either by chemical modification or by influencing chemical bioavailability. Among the metal pollutants, arsenic (As) is of major concern. As has become an important soil pollutant due to the use of As-based pesticides and fertilizers, geological activities, anthropogenic impacts, disposal of municipal and industrial wastes, and irrigation with As-contaminated water. As contamination represents an ecological and health problem due to its toxic effect and invasion into the food chain. An effective As remediation through common physico-chemical techniques is expensive and unsuitable for treating large contaminated areas effectively. Bioremediation with fungi offers a promising means to reclaim such contaminated soils in economical and eco-friendly ways. Fungi are able to tolerate, biosorb and detoxify arsenicals by several mechanisms including valence transformation, extra- and intra-cellular precipitation as well as through active uptake. Soil fungi play an important role in the environmental fate of As by affecting its transformations between soluble and insoluble forms as well as toxic and non-toxic forms. Soil fungi are also able to biomethylate inorganic As species to monomethylarsonic acid (MMAA), dimethylarsinic acid (DMAA) and trimethylarsine oxide (TMAO). It has also been shown that the fungal activity can result in volatilization of As into gaseous arsines. The response of soil fungi towards toxic As is of great importance in view of their use in the remediation of As-contaminated sites. Considering the above mechanisms of resistance and removal by fungi, it could be expected that screening of As-tolerant fungi isolated from As-contaminated sites may provide an effective approach to cleaning up As-polluted soils.