A microbial ecology survey of the Tinto River (pH between 2 and 2.5) allowed the isolation and characterization over a thousand acidophilic filamentous fungi. A systematic screening program using different acidophilic fungal isolates showed that most of them exhibited a high level of polymetallic resistance, and some of them a specific metal sequestering profile, a property with biotechnological potential. Penicillium sp. V80 was selected for further characterization due to its heavy metal resistance profile, its capacity to grow in the presence of high concentrations of chromium solutions (200 mM Cr~(3+) ), and to specifically sequester this metal with high efficiency (up to 75% at 100 mM chromium solution). Active growth was required for efficient chromium sequestering, suggesting the participation of an active transport system in the process. Scanning (SEM) and Transmission Electron Microscopy (TEM), together with Nuclear Microprobe Analysis (NMPA) has been used to evaluate possible mechanisms involved in specific Cr~(3+) sequestering by this fungal isolate.
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