Several species of fungi like Aspergillus niger, Penicillium simplicissimum are used for bioleaching. This form of leaching does not rely on microbial oxidation of metal, but rather uses microbial metabolism as source of acids which directly dissolve the metal.

Microfungi are heterotrophic organisms. They exist in all ecological niches, e. g. supporting the weathering of rocks as well as the mineralization of materials containing metals. Their development is encouraged by the acidic reaction, the presence of sugars, and the appropriate humidity. These microorganisms can produce large amounts of organic acids, such as citric, glycolic, oxalic, and other acids which work as chemical solvents, can be used on an industrial scale in bioleaching processes and impact the change of the environment’s reaction. The microfungi, due to their biochemistry and relatively high immunity to hostile factors (pH, temperature, etc.), provide an excellent alternative in the bioleaching of metals, since the classical chemical methods of acidic bioleaching cannot be used for environmental reasons. The extraction through microfungi consists mainly of producing metabolites like organic acids, amino acids, and peptides that serve as leaching agents for the dissolution of metals [11].

The metabolic process of fungi is similar to a great extent to those of higher plants with the exception of carbohydrate synthesis. The glycolytic pathway converts the glucose into variety of products including organic acids. So, these biomining processes are mediated due to the chemical attack by the extracted organic acids on the ores. The acids usually have dual effect of increasing metal dissolution by lowering the pH and increasing the load of soluble metals by complexion/chelating into soluble organic-metallic complexes [12].