『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 plasma-optical 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 discernible 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 on 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.』
1. Introduction
2. methods
2.1. General approach
2.2. Experimental methods
2.2.1. Bacterial preparation
2.2.2. Kinetics experiments
2.2.3. Batch precipitation experiments
2.2.4. Precipitation experiments using bacterial exudate solution
2.2.5. Biogenic mineral isolation
2.2.6. Solubility experiments
2.3. Analytical methods
2.3.1. TEM
2.3.2. XRD
2.3.3. Synchrotron experiments
2.3.4. ICP-OES
2.3.5. TOC
2.4. Thermodynamic modeling
2.4.1. Saturation states calculations
2.4.2. HUP solubility calculation
3. Results and discussion
3.1. Uranium system
3.1.1. TEM
3.1.2. SAED and XRD
3.1.3. XAS
3.1.4. ICP-OES
3.1.5. Solubility
3.1.6. Effects of bacteria on uranyl phosphate precipitation
3.2. Lead system
3.2.1. TEM
3.2.2. XRD
3.2.3. ICP-OES
3.2.4. Effect of bacteria on lead phosphate precipitation
3.3. Calcium system
3.3.1. TEM
3.3.2. XRD
3.3.3. ICP-OES
3.3.4. Effect of bacteria on calcium phosphate precipitation
4. Conclusions
Acknowledgments
Appendix A. Supplementary data
References