Fungi mediated detoxification of heavy metals: Insights on mechanisms, factors and recent

Wastewater originating from various industries is a major global environmental issue. The conventional methods utilized for the removal of HM are observed as inappropriate when the concentration of HMs is <100 mg/L. They also possess certain limitations such as the generation of secondary pollutants, high energy and chemicals requirement and are less economical. Consequently, detoxification of heavy metals using fungi has emerged as a viable solution as they have greater biosorption and bioaccumulation potential. Several environmental and operational factors such as pH and temperature, metal ion concentration, time and flow rate have major effects on the growth and metabolic functions of fungi. From the literature, it is observed that various organic acids, proteins and enzymatic and non-enzymatic antioxidants play a crucial role in HMs detoxification. Oxalic acid is considered the strongest chelating agent, as it forms insoluble and stable complexes. Various anionic structures present on the cell walls encourage fungi to bind or transform HMs and other contaminants by active uptake, intra and extracellular precipitation and valance transformation. Further, the synergistic effect of consortium provides a better metabolic network for the detoxification of highly contaminated sites. This review article outlines the mechanisms of metal detoxification via fungi and the role of secondary metabolites such as organic acids and enzymatic and non-enzymatic antioxidants in metal-stressed conditions. Numerous studies on prote-omics related to energy metabolism that significantly influences detoxification mechanisms are also highlighted. Finally, the localization of heavy metals in fungi and recent advancement in detoxification mechanisms are discussed.