Extracellular polymeric substances (EPS) produced by microorganisms play a crucial role in various bioprocesses, including bioleaching. The microbial leaching of metal sulfides requires an initial cell attachment, which is facilitated by EPS. These substances are mixtures of polysaccharides, proteins, lipids, and other compounds, and their composition and properties can vary depending on the species, growth conditions, and environmental factors. Despite the significance of iron/sulfur oxidizing species in biomining processes, the knowledge of the interfacial processes between thermoacidophilic archaeal species and mineral surfaces is limited. This study examines the cell surface characteristics and EPS produced by an Acidianus strain. The research was conducted using microscopic techniques, Zeta-potential measurements, spectrophotometric methods, Fourier transform infrared spectroscopy, and fluorescence lectin-binding analysis. The results suggest that non-soluble substrates, such as sulfur or pyrite, induce changes in cell surface structures, including the presence of cell appendages, wider cell envelopes, higher hydrophobicities, and increased EPS production, compared to cells grown with soluble substrates such as tetrathionate or ferrous iron. The EPS mainly consist of proteins and carbohydrates, including glucose, manose, N-acetylgalactosamine, and N-acetylglucosamine residues. This study contributes to a better understanding of the relationship between thermophilic archaea and mineral surfaces in biomining processes.

Studies of thermophilic microorganisms have shown that they have a considerable biotechnological potential due to their optimum growth and metabolism at high temperatures. Thermophilic archaea have unique characteristics with important biotechnological applications; many of these species could be used in bioleaching processes to recover valuable metals from mineral ores. Particularly, bioleaching at high temperatures using thermoacidophilic microorganisms can greatly improve metal solubilization from refractory mineral species such as chalcopyrite (CuFeS₂), one of the most abundant and widespread copper-bearing minerals. Interfacial processes such as early cell adhesion, biofilm development, and the formation of passive layers on the mineral surface play important roles in the initial steps of bioleaching processes. The present work focused on the investigation of different bioleaching conditions using the thermoacidophilic archaeon Acidianus copahuensis DSM 29038 to elucidate which steps are pivotal during the chalcopyrite bioleaching. Fluorescent in situ hybridization (FISH) and confocal laser scanning microscopy (CLSM) were used to visualize the microorganism–mineral interaction. Results showed that up to 85% of copper recovery from chalcopyrite could be achieved using A. copahuensis. Improvements in these yields are intimately related to an early contact between cells and the mineral surface. On the other hand, surface coverage by inactivated cells as well as precipitates significantly reduced copper recoveries.

The study and development of new sustainable mining methods to exploit low-grade ores and secondary metallic resources are essential to meet global demand and contribute to caring for the environment. Copper is one of the most widely used metals and chalcocite is the main secondary sulfide of this metal. Therefore, the study of copper recovery from chalcocite-dominant minerals could have a great impact on the industry. In this study, we assess at bench scale the feasibility of applying biohydrometallurgical processes to extract copper from chalcocite-rich minerals from Taca Taca, Argentina, using native mesophilic microorganisms (30 °C) and thermophiles (45, 65 °C). The indigenous mesophilic consortium was dominated by Acidithiobacillus ferrooxidans and could solubilize all the copper present in the systems (113 mg/L) within three weeks without any change in the pH of the solution. Notably, by increasing the temperature up to 45 and 65 °C, copper leaching was enhanced, completing the recovery in 7–14 days. The oxidizing microorganisms active in these conditions were Ferroplasma sp. and Acidianus copahuensis, respectively. An increase in the abiotic copper recovery was also observed as temperature rose; as well as a slight acidification of the solution. This study constitutes the first assessment for the bioleaching of Taca Taca ores.