Abstract
The biorecovery of europium (Eu) from primary (mineral deposits) and secondary (mining wastes) resources is of interest due to its remarkable luminescence properties, important for modern technological applications. In this study, we explored the tolerance levels, reduction and intracellular bioaccumulation of Eu by a site-specific bacterium, Clostridium sp. 2611 isolated from Phalaborwa carbonatite complex. Clostridium sp. 2611 was able to grow in minimal medium containing 0.5 mM Eu3+. SEM-EDX analysis confirmed an association between Eu precipitates and the bacterium, while TEM-EDX analysis indicated intracellular accumulation of Eu. According to the HR-XPS analysis, the bacterium was able to reduce Eu3+ to Eu2+ under growth and non-growth conditions. Preliminary protein characterization seems to indicate that a cytoplasmic pyruvate oxidoreductase is responsible for Eu bioreduction. These findings suggest the bioreduction of Eu3+ by Clostridium sp. as a resistance mechanism, can be exploited for the biorecovery of this metal.
Highlights
Rare earth metals are critical raw material for the development of modern technological products due to their magnetic, photo physical, fluorescent, spectroscopic and luminescent properties[1,2,3]
Very little information exists on how Clostridium species interact with Eu, especially we do not know how clostridia bioaccumulate Eu species
We aimed to investigate the ability of a Clostridium strain (C. sp 2611), isolated from sediments containing rare earth metals, to anaerobically reduce Eu3+ as a metal tolerance mechanism
Summary
Rare earth metals are critical raw material for the development of modern technological products due to their magnetic, photo physical, fluorescent, spectroscopic and luminescent properties[1,2,3]. Despite low concentrations, the large amounts of mining and industrial waste make these deposits an attractive source for rare earth metals[9,10]. In these environmental settings, site-specific microbes (e.g., Clostridium) are often exposed to metals without ‘adverse’ effects[11]. Several Clostridium strains have the ability to reduce and precipitate precious metals (i.e., Pd and Cu) as insoluble reduced compounds, bio-Pd (Pd0) and CuNP14,15. This feature can been exploited for biorecovery of precious metals in bioreactors under anaerobic conditions[16]. We aimed to investigate the ability of a Clostridium strain (C. sp 2611), isolated from sediments containing rare earth metals, to anaerobically reduce Eu3+ as a metal tolerance mechanism
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