Direct solid‐state evidence of H₂‐induced partial U(VI) reduction concomitant with adsorption by extracellular polymeric substances (EPS)

Abstract

Adsorption of hexavalent uranium (U(VI)) by extracellular polymeric substances (EPS) has been studied, but the possibility of simultaneous U(VI) reduction mediated by EPS has not had experimental confirmation, as the reduction products have not yet been directly proven. Here, we reported the first direct evidence of lower-valent products of U(VI) immobilization by loosely associated EPS (laEPS) isolated from a fermenter strain of Klebsiella sp. J1 when the laEPS was exposed to H . During the 120-min tests for similarly 86% adsorption under O , N , and H , 8% more U was immobilized through a non-adsorptive pathway by the EPS for H than for N and O . A set of solid-state characterization tools (FT-IR, XPS, EELS, and TEM-EDX) confirmed partial reduction of U(VI) to lower-valence U, with the main reduced form being uraninite (U O ) nanoparticles, and the results reinforced the role of the reduction in accelerating U immobilization and shaping the characteristics of immobilized U in terms of valency, size, and crystallization. The laEPS, mostly comprised of carbohydrate and protein, contained non-cytochrome enzymes and electron carriers that could be responsible for electron transfer to U(VI). Taken together, our results directly confirm that EPS was able to mediate partial U(VI) reduction in the presence of H through non-cytochrome catalysis and that reduction enhanced overall U immobilization. Our study fills in some gaps of the microbe-mediated U cycle and will be useful to understand and control U removal in engineered reactors and in-situ bioremediation.

Isolation and Identification of Uranium Tolerant Phosphate-Solubilizing Bacillus spp. and Their Synergistic Strategies to U(VI) Immobilization

“…EPS are metabolic products that accumulate on the surface of microbial cells and provide protection by reducing chemical exposure and stabilizing the membrane ( Teng et al, 2019b ). Previous studies have shown that EPS rich in functional groups and proteins were highly reactive with uranyl ions, suggesting that EPS could be used for rapid U adsorption ( Cao et al, 2011 ; Li et al, 2018 ). In this paper, our results indicated that the EPS generated by Bacillus spp.…”

Biosorption Mechanism of Aqueous Pb2+, Cd2+, and Ni2+ Ions on Extracellular Polymeric Substances (EPS)

“…Our previous researches focused on heavy metals or antibiotics adsorbed by bioflocculant MFX, which is one kind of EPS extracted from Klebsiella sp. J1 [31][32][33][34][35][36][37][38]. The results showed the great potential of EPS as water treatment materials and guided our subsequent studies.…”

Characteristics of Nitrogen Removal and Extracellular Polymeric Substances of a Novel Salt-Tolerant Denitrifying Bacterium, Pseudomonas sp. DN-23

“…ISTVK1 from heat-shocked sewage sludge, and this strain produced plenty of EPS during the removal of wastewater contaminants. Moreover, Li et al (2018) found that the EPS secreted by Klebsiella sp. J1 was able to immobilize hexavalent uranium [U(VI)] and mediate partial [U(VI)] reduction in the presence of H 2 .…”