Bio-sorption of neptunium(V) by Pseudomonas fluorescens

The complex puzzle of dietary silver nanoparticles, mucus and microbiota in the gut

Hundreds of consumer and commercial products containing silver nanoparticles (AgNPs) are currently used in food, personal-care products, pharmaceutical, and many other applications. Human exposure to AgNPs includes oral intake, inhalation, and dermal contact. The aim of this review was to focus on oral intake, intentional and incidental of AgNPs where well-known antimicrobial characteristics that might affect the microbiome and mucus in the gastrointestinal tract (GIT). This critical review summarizes what is known regarding the impacts of AgNPs on gut homeostasis. It is fundamental to understand the forms of AgNPs and their physicochemical characterization before and during digestion. For example, lab-synthesized AgNPs differ from "real" ingestable AgNPs used as food additives and dietary supplements. Similarly, the gut environment alters the chemical and physical state of Ag that is ingested as AgNPs. Emerging research on in vitro and in vivo rodent and human indicated complex multi-directional relationships among AgNPs, the intestinal microbiota, and the epithelial mucus. It may be necessary to go beyond today's descriptive approach to a modeling-based ecosystem approach that might quantitatively integrate spatio-temporal interactions among microbial groups, host factors (e.g., mucus), and environmental factors, including lifestyle-based stressors. It is suggested that future research (1) utilize more representative AgNPs, focus on microbe/mucus interactions, (2) assess the effects of environmental stressors for longer and longitudinal conditions, and (3) be integrated using quantitative modeling.

pH-dependent speciation and hydrogen (H2 ) control U(VI) respiration by Desulfovibrio vulgaris

In situ bioreduction of soluble hexavalent uranium U(VI) to insoluble U(IV) (as UO₂ ) has been proposed as a means of preventing U migration in the groundwater. This work focuses on the bioreduction of U(VI) and precipitation of U(IV). It uses anaerobic batch reactors with Desulfovibrio vulgaris, a well-known sulfate, iron, and U(VI) reducer, growing on lactate as the electron donor, in the absence of sulfate, and with a 30-mM bicarbonate buffering. In the absence of sulfate, D. vulgaris reduced  >90% of the total soluble U(VI) (1 mM) to form U(IV) solids that were characterized by X-ray diffraction and confirmed to be nano-crystalline uraninite with crystallite size 2.8 ± 0.2 nm. pH values between 6 and 10 had minimal impact on bacterial growth and end-product distribution, supporting that the mono-nuclear, and poly-nuclear forms of U(VI) were equally bioavailable as electron acceptors. Electron balances support that H₂ transiently accumulated, but was ultimately oxidized via U(VI) respiration. Thus, D. vulgaris utilized H₂ as the electron carrier to drive respiration of U(VI). Rapid lactate utilization and biomass growth occurred only when U(VI) respiration began to draw down the sink of H₂ and relieve thermodynamic inhibition of fermentation.

Rapid and efficient removal of Ni(2+) from aqueous solution by the one-pot synthesized EDTA-modified magnetic nanoparticles

A facile one-pot process has been proposed to prepare the novel ethylenediaminetetraacetic acid (EDTA)-modified magnetite nanoparticles (EDTA-MNPs). The bared Fe3O4 magnetite nanoparticles and EDTA-MNPs were characterized using FTIR spectroscopy, TEM, VSM, and X-ray diffraction. The application of the modified magnetite nanoparticles for metal ion uptake was studied using Ni(2+) as a model. The adsorption was fast and the equilibrium was established within 5 min, and the adsorption kinetics of Ni(2+) onto EDTA-MNPs followed the pseudo second-order chemisorption mechanism. Maximum adsorption capacity for Ni(2+) reached as high as 41.3 mg/g at pH 6. The successive adsorption-desorption studies indicated that the EDTA-MNPs kept the adsorption and desorption efficiencies constant over ten cycles. Importantly, EDTA-MNPs were able to remove nearly 100 % of Ni(2+) from real water.

Surface complexation of Neptunium(V) onto whole cells and cell components of Shewanella alga: modeling and experimental study

We systematically quantified surface complexation of Np(V) onto whole cells, cell wall, and extracellular polymeric substances (EPS) of Shewanella alga strain BrY. We first performed acid and base titrations and used the mathematical model FITEQL to estimate the concentrations and deprotonation constants of specific surface functional groups. Deprotonation constants most likely corresponded to a carboxyl group not associated with amino acids (pK(a) approximately 5), a phosphoryl site (pK(a) approximately 7.2), and an amine site (pK(a) > 10). We then carried out batch sorption experiments with Np(V) and each of the S. alga components as a function of pH. Since significant Np(V) sorption was observed on S. alga whole cells and its components in the pH range 2-5, we assumed the existence of a fourth site: a low-pK(a) carboxyl site (pK(a) approximately 2.4) that is associated with amino acids. We used the SPECIATE submodel of the biogeochemical model CCBATCH to compute the stability constants for Np(V) complexation to each surface functional group. The stability constants were similar for each functional group on S. alga bacterial whole cells, cell walls, and EPS, and they explain the complicated sorption patterns when they are combined with the aqueous-phase speciation of Np(V). For pH < 8, the aquo NpO(2)(+) species was the dominant form of Np(V), and its log K values for the low-pK(a) carboxyl, mid-pK(a) carboxyl, and phosphoryl groups were 1.8, 1.8, and 2.5-3.1, respectively. For pH greater than 8, the key surface ligand was amine >XNH(3)(+), which complexed with NpO(2)(CO(3))(3)(5-). The log K for NpO(2)(CO(3))(3)(5-) complexed onto the amine groups was 3.1-3.9. All of the log K values are similar to those of Np(V) complexes with aqueous carboxyl and N-containing carboxyl ligands. These results help quantify the role of surface complexation in defining actinide-microbiological interactions in the subsurface.

A biogeochemical framework for metal detoxification in sulfidic systems

We develop a comprehensive biogeochemical framework for understanding and quantitatively evaluating metals bio-protection in sulfidic microbial systems. We implement the biogeochemical framework in CCBATCH by expanding its chemical equilibrium and biological sub-models for surface complexation and the formation of soluble and solid products, respectively. We apply the expanded CCBATCH to understand the relative importance of the various key ligands of sulfidic systems in Zn detoxification. Our biogeochemical analysis emphasizes the relative importance of sulfide over other microbial products in Zn detoxification, because the sulfide yield is an order of magnitude higher than that of other microbial products, while its reactivity toward metals also is highest. In particular, metal-titration simulations using the expanded CCBATCH in a batch mode illustrate how sulfide detoxifies Zn, controlling its speciation as long as total sulfide is greater than added Zn. Only in the absence of sulfide does complexation of Zn to biogenic organic ligands play a role in detoxification. Our biogeochemical analysis conveys fundamental insight on the potential of the key ligands of sulfidic systems to effect Zn detoxification. Sulfide stands out for its reactivity and prevalence in sulfidic systems.

Influence of in situ biofilm coverage on the radionuclide adsorption capacity of subsurface granite

Any migration of radionuclides from nuclear waste repositories is expected to be mitigated by adsorption to the host rocks surrounding hydraulically conductive fractures. Fluid rock interfaces are considered to be important barriers for nuclear waste disposal schemes but their adsorptive capacity can be affected by the growth of microbial biofilms. This study indicates that biofilms growing on fracture surfaces decrease the rocks adsorption capacity for migrating radionuclides except for trivalent species. Potential suppression of adsorption by biofilms should, therefore, be accounted for in performance safety assessment models. In this study, the adsorptive capacity of in situ anaerobic biofilms grown 450 m underground on either glass or granite slides was compared to the capacity of the same surfaces without biofilms. Surfaces were exposed to the radiotracers 60Co(II), 147Pm(III), 241Am(III), 234Th(IV), and 237Np(V) for a period of 660 h in a pH neutral anaerobic synthetic groundwater. Adsorption was investigated at multiple time points over the 660 h using liquid scintillation and ICP-MS. Results indicate that these surfaces adsorb between 0 and 85% of the added tracers under the conditions of the specific experiments. After 660 h, the distribution coefficients, R (ratio between what is sorbed and what is left in the aqueous phase), approached 3 x 10(4) m for 60Co, 3 x 10(5) m for 147Pm and 241Am, 1 x 10(6)m for 234Th, and 1 x 10(3) m for 237Np. The highest rate of adsorption was during the first 200 h of the adsorption experiments and started to approach equilibrium after 500 h. Adsorption to colloids and precipitates contributed to decreases of up to 20% in the available 60Co, 147Pm, 241Am, and 237Np in the adsorption systems. In the 234Th system 95% of the aqueous 234Th was removed by adsorbing to colloids. Although the range of Rvalues for each surface tested generally overlapped, the biofilms consistently demonstrated lower R values except for the trivalant 147Pm and 241Am adsorption systems.