Uptake and transformation of arsenic by Acidomyces acidophilus isolated from acidic mine tailings and its toxigenic implications.

Adequate treatment and safe disposal of high-acidity effluents generated during mining containing elevated concentrations of heavy metals and metalloids, such as arsenic, are a critical environmental challenge. In this work, we isolated and characterized an acidophilic fungus from acid mine drainage-affected tailings pond sludge containing high levels of heavy metals. This fungus was identified as Acidomyces acidophilus strain MSS1 and was characterized by its capacity to tolerate and metabolize As(V) and As(III). Our results show that As tolerance and removal capacity by this fungus is highly dependent on pH, being more effective at pH 3.0 than pH 5.4. The biotransformation mechanism involves internalization of As species, As(V) reduction to As(III), and possible biomethylation. It is also capable of oxidizing As(III) in the medium to As(V) to a lesser extent. Arsenite methyltransferase expression was upregulated in the presence of As(III), increasing approximately 25-fold at pH 3 and approximately 14-fold at pH 5.4, compared with fungus not exposed to As. However, in the presence of As(V), it only increased approximately five-fold at pH 5.4; thus, methylation of As is highly dependent on pH and the type of As species present. Additionally, As was removed by biosorption to the fungal biomass. Overall, our results suggest that A. acidophilus can be considered as a potential As bioremediation agent for the removal of As, in particular As(III), in highly acidic effluents, due to its remarkable tolerance to low pH and high metal concentrations.