The effect of natural organic matter on the adsorption of mercury to bacterial cells

We investigated the ability of non-metabolizing Bacillus subtilis, Shewanella oneidensis MR-1, and Geobacter sulfurreducens bacterial species to adsorb mercury in the absence and presence of Suwanee River fulvic acid (FA). Bulk adsorption and X-ray absorption spectroscopy (XAS) experiments were conducted at three pH conditions, and the results indicate that the presence of FA decreases the extent of Hg adsorption to biomass under all of the pH conditions studied. Hg XAS results show that the presence of FA does not alter the binding environment of Hg adsorbed onto the biomass regardless of pH or FA concentration, indicating that ternary bacteria–Hg–FA complexes do not form to an appreciable extent under the experimental conditions, and that Hg binding on the bacteria is dominated by sulfhydryl binding. We used the experimental results to calculate apparent partition coefficients, Kd, for Hg under each experimental condition. The calculations yield similar coefficients for Hg onto each of the bacterial species studies, suggesting there is no significant difference in Hg partitioning between the three bacterial species. The calculations also indicate similar coefficients for Hg–bacteria and Hg–FA complexes. S XAS measurements confirm the presence of sulfhydryl sites on both the FA and bacterial cells, and demonstrate the presence of a wide range of S moieties on the FA in contrast to the bacterial biomass, whose S sites are dominated by thiols. Our results suggest that although FA can compete with bacterial binding sites for aqueous Hg, because of the relatively similar partition coefficients for the types of sorbents, the competition is not dominated by either bacteria or FA unless the concentration of one type of site greatly exceeds that of the other

Stoichiometry of mercury-thiol complexes on bacterial cell envelopes

We have examined the speciation of Hg(II) complexed with intact cell suspensions (1013 cells L− 1) of Bacillus subtilis, a common gram-positive soil bacterium, Shewanella oneidensis MR-1, a facultative gram-negative aquatic organism, and Geobacter sulfurreducens, a gram-negative anaerobic bacterium capable of Hg-methylation at Hg(II) loadings spanning four orders of magnitude (120 nM to 350 μM) at pH 5.5 (± 0.2). The coordination environments of Hg on bacterial cells were analyzed using synchrotron based X-ray Absorption Near Edge Structure (XANES) and Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy at the Hg LIII edge. The abundance of thiols on intact cells was determined by a fluorescence-spectroscopy based method using a soluble bromobimane, monobromo(trimethylammonio)bimane (qBBr) to block thiol sites, and potentiometric titrations of biomass with and without qBBr treatment. The chemical forms of S on intact bacterial cells were determined using S k-edge XANES spectroscopy. Hg(II) was found to complex entirely with cell bound thiols at low Hg:biomass ratios. For Bacillus subtilis and Shewanella oneidensis MR-1 cells, the Hg—S stoichiometry changed from Hg—S₃ to Hg—S₂ and Hg—S (where ‘S’ represents a thiol site such as is present on cysteine) progressively as the Hg(II) loading increased on the cells. However, Geobacter sulfurreducens did not form Hg—S₃ complexes. Because the abundance of thiol was highest for Geobacter sulfurreducens (75 μM/g wet weight) followed by Shewanella oneidensis MR-1 (50 μM/g wet weight) and Bacillus subtilis (25 μM/g wet weight), the inability of Hg(II) to form Hg—S₃ complexes on Geobacter sulfurreducens suggests that the density and reactivity of S-amino acid containing cell membrane proteins on Geobacter sulfurreducens are different from those of Bacillus subtilis and Shewanella oneidensis MR-1. Upon saturation of the high affinity thiol sites at higher Hg:biomass ratios, Hg(II) was found to form a chelate with α-hydroxy carboxylate anion. The stoichiometry of cell envelope bound Hg-thiol complexes and the associated abundance of thiols on the cell envelopes provide important insights for understanding the differences in the rate and extent of uptake and redox transformations of Hg in the environment

Systemic Anticancer Therapy and Thromboembolic Outcomes in Hospitalized Patients With Cancer and COVID-19

IMPORTANCE: Systematic data on the association between anticancer therapies and thromboembolic events (TEEs) in patients with COVID-19 are lacking. OBJECTIVE: To assess the association between anticancer therapy exposure within 3 months prior to COVID-19 and TEEs following COVID-19 diagnosis in patients with cancer. DESIGN, SETTING, AND PARTICIPANTS: This registry-based retrospective cohort study included patients who were hospitalized and had active cancer and laboratory-confirmed SARS-CoV-2 infection. Data were accrued from March 2020 to December 2021 and analyzed from December 2021 to October 2022. EXPOSURE: Treatments of interest (TOIs) (endocrine therapy, vascular endothelial growth factor inhibitors/tyrosine kinase inhibitors [VEGFis/TKIs], immunomodulators [IMiDs], immune checkpoint inhibitors [ICIs], chemotherapy) vs reference (no systemic therapy) in 3 months prior to COVID-19. MAIN OUTCOMES AND MEASURES: Main outcomes were (1) venous thromboembolism (VTE) and (2) arterial thromboembolism (ATE). Secondary outcome was severity of COVID-19 (rates of intensive care unit admission, mechanical ventilation, 30-day all-cause mortality following TEEs in TOI vs reference group) at 30-day follow-up. RESULTS: Of 4988 hospitalized patients with cancer (median [IQR] age, 69 [59-78] years; 2608 [52%] male), 1869 had received 1 or more TOIs. Incidence of VTE was higher in all TOI groups: endocrine therapy, 7%; VEGFis/TKIs, 10%; IMiDs, 8%; ICIs, 12%; and chemotherapy, 10%, compared with patients not receiving systemic therapies (6%). In multivariable log-binomial regression analyses, relative risk of VTE (adjusted risk ratio [aRR], 1.33; 95% CI, 1.04-1.69) but not ATE (aRR, 0.81; 95% CI, 0.56-1.16) was significantly higher in those exposed to all TOIs pooled together vs those with no exposure. Among individual drugs, ICIs were significantly associated with VTE (aRR, 1.45; 95% CI, 1.01-2.07). Also noted were significant associations between VTE and active and progressing cancer (aRR, 1.43; 95% CI, 1.01-2.03), history of VTE (aRR, 3.10; 95% CI, 2.38-4.04), and high-risk site of cancer (aRR, 1.42; 95% CI, 1.14-1.75). Black patients had a higher risk of TEEs (aRR, 1.24; 95% CI, 1.03-1.50) than White patients. Patients with TEEs had high intensive care unit admission (46%) and mechanical ventilation (31%) rates. Relative risk of death in patients with TEEs was higher in those exposed to TOIs vs not (aRR, 1.12; 95% CI, 0.91-1.38) and was significantly associated with poor performance status (aRR, 1.77; 95% CI, 1.30-2.40) and active/progressing cancer (aRR, 1.55; 95% CI, 1.13-2.13). CONCLUSIONS AND RELEVANCE: In this cohort study, relative risk of developing VTE was high among patients receiving TOIs and varied by the type of therapy, underlying risk factors, and demographics, such as race and ethnicity. These findings highlight the need for close monitoring and perhaps personalized thromboprophylaxis to prevent morbidity and mortality associated with COVID-19-related thromboembolism in patients with cancer

Distribution of Protons and Cd between Bacterial Surfaces and Dissolved Humic Substances Determined through Chemical Equilibrium Modeling

Bacteria and dissolved humic substances are capable of binding significant concentrations of metals in natural environments. Recent advances in understanding bacteria-metal and humic-metal complexation have provided a framework for directly comparing the binding capacities of these components. In this study, we use chemical equilibrium modeling to construct an internally consistent set of thermodynamic equilibrium constants for proton and Cd binding onto dissolved humic substances, using a variety of published data sets. Our modeling approach allows for the direct comparison of humic substance binding constants and site densities to those previously published for proton and Cd binding onto natural consortia of bacteria. We then combine these constants into a unified model that accounts for the competition between bacterial surfaces and humic and fulvic acids in order to determine the relative importance of each component on the total Cd budget. The combined model is used to examine the relative contributions of bacteria and dissolved humic substances to Cd complexation in natural settings. Calculations are performed for three representative systems: (1) one with a maximum realistic concentration of bacteria and a minimum realistic concentration of humic substance, (2) one with a maximum realistic concentration of humic substance and a minimum concentration of bacteria, and (3) one with an intermediate concentration of both components.Our modeling results indicate that dissolved humic substances have 2 orders of magnitude more available binding sites than bacterial surfaces (per gram). Humic substances also have a greater affinity than bacterial surfaces for binding Cd over circumneutral pH ranges. The combined model results demonstrate that, depending upon their relative concentrations, both Cd-humic and Cd-bacteria complexes are capable of dominating Cd-speciation in specific natural environments. This modeling approach is useful in that it can easily be extended to include other metals and binding ligands; however, thermodynamic data must be gathered on additional components to facilitate the modeling of more realistic systems

The Impact of Ionic Strength on the Adsorption of Protons, Pb, Cd, and Sr onto the Surfaces of Gram Negative Bacteria: Testing Non-Electrostatic, Diffuse, and Triple-Layer Models

Bacterial surface adsorption reactions are influenced by electric field effects caused by changes in ionic strength; however, existing datasets are too sparse to definitively constrain these differences or to determine the best way to account for them using thermodynamic models. In this study, we examine the ionic strength dependence of proton and metal adsorption onto the surfaces of Pseudomonas mendocina and Pseudomonas putida by conducting proton, Cd(II), Pb(II), and Sr(II) adsorption experiments over the ionic strength range of 0.001 to 0.6 M. Chosen experimental results are thermodynamically modeled using a non-electrostatic approach, a diffuse layer model (DLM), and a triple-layer model (TLM). The results demonstrate that bacterial surface electric field effects are negligible for proton, Cd, and Pb adsorption onto P. putida and P. mendocina, and that the discrete site non-electrostatic model developed in this study is adequate for describing these reactions. The extent of Sr adsorption is influenced by changes in the bacterial surface electric field; however, the non-electrostatic model better describes Sr adsorption behavior than the DLM or TLM. The DLM and TLM greatly overpredict the effect of the electric field for all adsorption reactions at all ionic strengths tested

Cadmium adsorption to mixtures of soil components: Testing the component additivity approach

The ability to predict the distribution of metals in geologic systems requires a modeling approach that can describe the competition among adsorbing surfaces for the metal of interest. In this study, we test if a component additivity (CA) surface complexation approach can account for the distribution of Cd(II) in mixtures of kaolinite, Bacillus subtilis bacterial cells, iron oxyhydroxide, and a dissolved organic ligand, acetate. We use existing surface complexation models to define the stoichiometries, acidity constants, and site concentrations for the important surface species on each of the sorbents, and we conduct Cd adsorption experiments with each sorbent individually to determine the stability constants for the important Cd-surface complexes on each sorbent. We test the CA approach by comparing CA predictions to measured extents of Cd adsorption in two-, three-, and four-component mixtures of the sorbents at various ratios. Our results indicate that for systems containing B. subtilis, iron oxyhydroxide, and kaolinite, the CA approach is a reasonable predictor of metal distribution, with the accuracy limited by the accuracy of the stability constants of the important surface complexes. However, in systems including acetate, the CA predictions significantly underestimate the extent of adsorption above pH 5, likely due to the formation of ternary Cd-acetate surface complexes on each surface. Metal-organic-surface ternary complexation and site blockage of one sorbent by another are two possible limitations of the applicability of CA surface complexation models to realistic geologic systems. (C) 2009 Elsevier B.V. All rights reserved

Significance of Ternary Bacteria-metal-natural Organic Matter Complexes Determined through Experimentation and Chemical Equilibrium Modeling

In this study, we conducted experiments that tested for the existence of ternary surface complexes involving bacteria, metal cations and natural organic matter (NOM). We performed a variety of batch complexation experiments in single (NOM only), binary (Bacillus subtilis-metal, NOM-metal, B. subtilis-NOM), and ternary (B. subtilis-metal-NOM) systems in order to determine the significance of ternary complexation. We conducted experiments as a function of 1) pH, 2) component concentrations, 3) fraction of NOM (humic, fulvic, or bulk), and 4) metal of interest (Pb, Cu, Cd, and Ni). Our investigative approach was to quantify the differences between the binary and ternary experimental systems under these different conditions. The concentration of NOM bound in ternary form was calculated directly from experimental data by comparing binary and ternary systems. The concentration of metal bound in ternary form was calculated using chemical equilibrium modeling.Experimental results demonstrate that bacteria-metal-NOM complex formation is a rapid, fully-reversible chemical process. The pH of the aqueous system is the biggest factor in the stability, and therefore significance of ternary complexes. As pH decreases, bacteria-metal-NOM complexes become more stable. The fraction of NOM involved and the identity of the aqueous metal cation have a comparatively modest impact on the stability of ternary complexes. All NOM fractions form ternary complexes to similar extents at circumneutral pH, but humic acid becomes the dominant NOM fraction in ternary complexes at low pH. The abundance of humic acid in ternary form is greatest in experimental systems with Ni or Cd and less in systems with Pb and Cu.These observations suggest that bacteria-metal-NOM complexes are abundant under the conditions present in most natural waters. Hence, ternary complexes may impact the mobility of aqueous metal cations in natural systems by changing dissolved NOM-metal complexes to colloidal bacteria-metal-NOM complexes

Enhanced Removal of Dissolved Hg(II), Cd(II), and Au(III) from Water by <i>Bacillus subtilis</i> Bacterial Biomass Containing an Elevated Concentration of Sulfhydryl Sites

In this study, the sorption of Hg­(II), Cd­(II), and Au­(III) onto <i>Bacillus subtilis</i> biomass with an elevated concentration of sulfhydryl sites, induced by adding excess glucose to the growth medium (termed ‘High Sulfhydryl <i>Bacillus subtilis</i>’ or HSBS) was compared to that onto <i>B. subtilis</i> biomass with a low concentration of sulfhydryl sites (termed ‘Low Sulfhydryl <i>Bacillus subtilis</i>’ or LSBS) and to sorption onto a commercially available cation exchange resin. Our results show that HSBS exhibits sorption capacities for the three studied metals that are two to five times greater than the sorption capacities of LSBS for these metals. After blocking the bacterial cell envelope sulfhydryl sites using a qBBr treatment, the sorption of the metals onto HSBS was significantly inhibited, indicating that the enhanced sorption onto HSBS was mainly due to the elevated concentration of sulfhydryl sites on the bacteria. A direct comparison of the removal capacity of the HSBS and that of the cation exchange resin for the three metals demonstrates that HSBS, compared to this commercially available resin, exhibits superior sorption capacity and selectivity for the removal of Hg­(II), Cd­(II), and Au­(III), especially in systems with dilute metal concentrations. These results suggest that bacterial sulfhydryl sites control the sorption behavior of these three metals, and therefore biomass with induced high concentrations of sulfhydryl sites represents a promising and low cost biosorbent for the effective removal and recovery of chalcophile heavy metals from aqueous media