The effects of non-metabolizing bacterial cells on the precipitation of U, Pb and Ca phosphates

Abstract

In this study, we test the potential for passive cell wall biomineralization by determining the effects of non-metabolizing bacteria on the precipitation of uranyl, lead, and calcium phosphates from a range of over-saturated conditions. Experiments were performed using Gram-positive Bacillus subtilis and Gram-negative Shewanella oneidensis MR-1. After equilibration, the aqueous phases were sampled and the remaining metal and P concentrations were analyzed using inductively coupled plasmaoptical emission spectroscopy (ICP-OES); the solid phases were collected and analyzed using X-ray diffractometry (XRD), transmission electron microscopy (TEM), and X-ray absorption spectroscopy (XAS).At the lower degrees of over-saturation studied, bacterial cells exerted no discernable effect on the mode of precipitation of the metal phosphates, with homogeneous precipitation occurring exclusively. However, at higher saturation states in the U system, we observed heterogeneous mineralization and extensive nucleation of hydrogen uranyl phosphate (HUP) mineralization throughout the fabric of the bacterial cell walls. This mineral nucleation effect was observed in both B. subtilis and S. oneidensis cells. In both cases, the biogenic mineral precipitates formed under the higher saturation state conditions were significantly smaller than those that formed in the abiotic controls.The cell wall nucleation effects that occurred in some of the U systems were not observed under any of the saturation state conditions studied in the Pb or Ca systems. The presence of B. subtilis significantly decreased the extent of precipitation in the U system, but had little effect in the Pb and Ca systems. At least part of this effect is due to higher solubility of the nanoscale HUP precipitate relative to macroscopic HUP. This study documents several effects of non-metabolizing bacterial cells on the nature and extent of metal phosphate precipitation. Each of these effects likely contributes to higher metal mobilities in geologic media, but the effects are not universal, and occur only with some elements and only under a subset of the conditions studied.

Pore‐scale evaluation of uranyl phosphate precipitation in a model groundwater system

“…Precipitates of chernikovite were recently observed by XRD, SEM (or transmission electron microscope), and/or EXAFS (Extended X‐ray adsorption fine structure) in batch studies under uranium and phosphate concentrations similar to those used in the UP system of this study [ Singh et al ., ; Dunham‐Cheatham et al ., ]. In those studies, thermodynamically more favorable solid forms other than chernikovite were not observed as in this study.…”

“…[] and Dunham‐Cheatham et al . []), and abiotic reactions including adsorption and mineral precipitation [ Morrison and Spangler , ; Naftz et al ., ; Gabriel et al ., ; United States Environmental Protection Agency ( USEPA ), ; Simon and Biermann , ; Wellman et al ., ; Hiemstra et al ., ]. Among these approaches, abiotic precipitation has received considerable attention due to its success in uranium removal from soil and groundwater [ Arey et al ., ; USEPA , ; Fuller et al ., ; Simon et al ., ].…”

The effect of metal loading on Cd adsorption onto Shewanella oneidensis bacterial cell envelopes: The role of sulfhydryl sites

“…Bacteria are ubiquitous in near-surface environments, and they can adsorb a wide range of metals through interactions with their abundant cell envelope binding sites Murray, 1976, 1980;Plette et al, 1996;Fein et al, 1997), thereby affecting the speciation, distribution and mobility of metals in these systems (Beveridge and Murray, 1976;Templeton et al, 2001;Li and Wong, 2010). Bacterial adsorption of metal also can promote biomineralization reactions (Beveridge et al, 1983;Labrenz et al, 2000;Dunham-Cheatham et al, 2011) and can control metal bioavailability for a range of metabolic processes Hu et al, 2013;Flynn et al, 2014;Sheng and Fein, 2014). Determining the mechanisms responsible for metal adsorption onto bacterial cells, therefore, is critical in order to understand global cycling and transformation of many metals in the environment.…”

The mechanism of uranium transformation from U(VI) into nano-uramphite by two indigenous Bacillus thuringiensis strains

“…In addition to above-mentioned reductive biomineralization of uranium, previous studies have also been primarily focused on the nonreductive biomineralization of U(VI) phosphate by microbes [10,[16][17][18][19][20][21]. However, a comprehensive study on the transformation of uranium is still missing.…”