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

Abstract

This study investigates the impact of specific environmental conditions on the formation of colloidal U(IV) nanoparticles by the sulfate reducing bacteria (SRB, Desulfovibrio alaskensis G20). The reduction of soluble U(VI) to less soluble U(IV) was quantitatively investigated under growth and non-growth conditions in bicarbonate or 1,4-piperazinediethanesulfonic acid (PIPES) buffered environments. The results showed that under non-growth conditions, the majority of the reduced U nanoparticles aggregated and precipitated out of solution. High resolution transmission electron microscopy revealed that only a very small fraction of cells had reduced U precipitates in the periplasmic spaces in the presence of PIPES buffer, whereas in the presence of bicarbonate buffer, reduced U was also observed in the cytoplasm with greater aggregation of biogenic U(IV) particles at higher initial U(VI) concentrations. The same experiments were repeated under growth conditions using two different electron donors (lactate and pyruvate) and three electron acceptors (sulfate, fumarate, and thiosulfate). In contrast to the results of the non-growth experiments, even after 0.2 μm filtration, the majority of biogenic U(IV) remained in the aqueous phase resulting in potentially mobile biogenic U(IV) nanoparticles. Size fractionation results showed that U(IV) aggregates were between 18 and 200 nm in diameter, and thus could be very mobile. The findings of this study are helpful to assess the size and potential mobility of reduced U nanoparticles under different environmental conditions, and would provide insights on their potential impact affecting U(VI) bioremediation efforts at subsurface contaminated sites.

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

“…The metal reduction commonly observed in bacterial cultures may be due to direct (bacterial activity), indirect (electron shuttle) and abiotic reduction (due to media constituents), which are not mutually exclusive. For instance, all these mechanisms have been observed in Desulfovibrio alaskensis G20 49 . In this study, non-growing conditions were selected to exclude metal reduction from growth-related cellular processes and stimulate competition for limited substrates 50,51 , as the only electron acceptor was Eu 3+ .…”

An overview of heavy metal removal from wastewater using magnetotactic bacteria

“…In many published reports, biogenic NPs have drawbacks in wastewater treatment systems including (i) less stability for long‐term applications, (ii) leaching, detachment and disintegration/aggregation from bacterial biomass due to variations in operating conditions (e.g. pH, temperature, influent concentration, shaking speed and contact time), (iii) lack of reusability, regeneration and biomass separation capabilities, (iv) consumption of expensive metal salt solutions and handling requirements of the bacteria that increase fabrication costs which eventually would increase treatment cost, and (v) sludge toxicity and biomass separation from final effluents . MTB‐based treatment technology, however, offers various advantages including (i) the unique property of MTB moving/swimming along the applied external magnetic field because of their nano sized MS reduces the cost required for the modification of fabricated NPs, and (ii) sludge toxicity and biomass separation issues can be minimized because MTB can be easily separated from final effluents without facing problems such as leaching, detachment and disintegration/ aggregation .…”