Impact of different environmental conditions on the aggregation of biogenic U(IV) nanoparticles synthesized by Desulfovibrio alaskensis G20

Phytoremediation of radioactive elements, possibilities and challenges: special focus on agricultural aspects

The radioactive contamination has been reported frequently from agricultural lands and ground water. The main reason behind the radioactive pollution is unprotected mining of radioactive elements, unsafe discard of nuclear industrial waste, military applications, dumping of medically used radioisotopes, globally situated (>400) nuclear power plants and use of phosphate fertilizers in farming. Radionuclides are well known potent carcinogens that may cause the various types of cancers to human and animals due to the long exposure to radioactive contaminated sites. To get rid of from the radioactive pollution there is a need of practically successful and cost effective bioremediation technologies that should able to decontaminate the effected lands and water to benefit the mankind. Microbial and phytoremediation are well studied methods for decreasing or gradually eliminating the radioactive contaminants. In this review, we discussed the different strategies of microbial and phytoremediation of radionuclides and recent advancements, that can play the major role in bioremediation of soil and water.

Mechanism of efficient remediation of U(VI) using biogenic CMC-FeS complex produced by sulfate-reducing bacteria

Uranium in groundwater during uranium mining activities urgently needs to be remediated through effective and environmental-friendly approaches. The reduction and immobilization of soluble U(VI) using biogenic carboxymethyl cellulose modified iron sulfide complex (biogenic CMC-FeS complex) is one of the emerging and innovative methods. However, its removal mechanism is largely unknown. Here, biogenic CMC-FeS complex with extracellular polymeric substances (EPS) and CMC was successfully synthesized by sulfate-reducing bacteria (SRB) and showed highly dispersible capacity. The tryptophan and tyrosine, which were the main components in EPS produced by SRB on CMC-FeS surface, significantly increased the U(VI) removal capacity of the biogenic CMC-FeS complex compared with chemically synthesized CMC-FeS. U(VI) removal was attributed to the adsorption of soluble U(VI) by ≡FeO⁺, CMC, tryptophan, and tyrosine on the biogenic CMC-FeS complex, following its reduction by S^2-, S₂^2- and Fe²⁺. Moreover, biogenic CMC-FeS complex with CMC-to-FeS molar ratio of 0.0005 performed well in the presence of bicarbonate (5 mM), humic acid (10 mg/L), or co-existing cations such as Pb²⁺, Ni²⁺, Cd²⁺, Mn^2+, and Cu²⁺ (200 ug/L) at pH 7.0, and displayed relatively high oxidation resistance and stability ability. This work provides an in-depth understanding of the biogenic CMC-FeS complex for the U(VI) removal and contributes to the development of cost-effective U(VI) remediation technologies.

Anaerobic reduction of europium by a Clostridium strain as a strategy for rare earth biorecovery

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.