Bioleaching of Manganese Oxides at Different Oxidation States by Filamentous Fungus Aspergillus niger

Abstract

This work aimed to examine the bioleaching of manganese oxides at various oxidation states (MnO, MnO·Mn2O3, Mn2O3 and MnO2) by a strain of the filamentous fungus Aspergillus niger, a frequent soil representative. Our results showed that the fungus effectively disintegrated the crystal structure of selected mineral manganese phases. Thereby, during a 31-day static incubation of oxides in the presence of fungus, manganese was bioextracted into the culture medium and, in some cases, transformed into a new biogenic mineral. The latter resulted from the precipitation of extracted manganese with biogenic oxalate. The Mn(II,III)-oxide was the most susceptible to fungal biodeterioration, and up to 26% of the manganese content in oxide was extracted by the fungus into the medium. The detected variabilities in biogenic oxalate and gluconate accumulation in the medium are also discussed regarding the fungal sensitivity to manganese. These suggest an alternative pathway of manganese oxides’ biodeterioration via a reductive dissolution. There, the oxalate metabolites are consumed as the reductive agents. Our results highlight the significance of fungal activity in manganese mobilization and transformation. The soil fungi should be considered an important geoactive agent that affects the stability of natural geochemical barriers.

Involvement of Bacterial and Fungal Extracellular Products in Transformation of Manganese-Bearing Minerals and Its Environmental Impact

“…Since acidolysis can be an alternative or co-occurring pathway of manganese oxides' deterioration [131], the acidification of culture media facilitates the manganese oxides' dissolution [17]. Still, acidification is only partially responsible for the manganese bioextraction and plays a secondary role compared to reductive dissolution [128].…”

“…Other than the aforementioned factors, the extent of Mn(II) extraction from the manganese-bearing minerals and ores by filamentous fungi is influenced by various other factors, such as pulp density of manganese mineral and composition of manganese ore, and temperature. The strain of Aspergillus niger managed to extract 91% of manganese from oceanic polymetallic nodules (5% w/v) [134], 69% from the synthetic Mn 3 O 4 [17] and 78.8% from the low-grade pyrolusite [135]. Fungus Aspergillus oryzae reached the maximum of 79% extraction efficiency under optimized conditions (pH 6, 37 • C, 2% pulp density of manganese ore and dextrose as carbon source) [125].…”

“…Furthermore, when evaluating the manganese extraction efficiency, we also need to take into account the readsorption of Mn(II) ions onto the solid manganese phases [136], as well as the precipitation of biogenic mineral phases [17]. In a culture medium, the elevated concentration of Mn(II) and accumulated extracellular oxalate allows the formation of secondary minerals, including manganese oxalate trihydrate (falottaite) and manganese oxalate dihydrate (lindbergite) [65,137].…”

“…However, the formation of manganese oxalate phases can be beneficial for the producing microorganism. The elevated dissolved concentrations of Mn could have inhibiting effects towards microbial growth, and therefore, complexation of Mn onto oxalate phases possess indirect detoxification effects/outcomes in the case of the fungus A. niger [17]. In addition to the favorable outcomes for microorganisms, the formation of oxalate phases also influences the geochemistry of some potentially toxic elements, e.g., arsenic [65].…”

“…These processes are primarily mediated by the redox and protolytic reactions, in which the microorganisms (both bacteria and fungi) may be involved directly or indirectly [15,16]. Consequently, microorganisms possess an exceptional ability to deteriorate and transform the manganese-bearing minerals, thus, altering their reactivity and stability in the environment [17][18][19]. However, the biodeterioration of manganese oxides in natural geochemical barriers may also contribute to releasing associated potentially hazardous elements [3,[18][19][20], adversely affecting the environment's vitality [21].…”