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Title: Multiple Mechanisms of Uranium Immobilization by Cellulomonas sp. Strain ES6

Abstract

Removal of hexavalent uranium (U(VI)) from aqueous solution was studied using a Gram-positive facultative anaerobe, Cellulomonas sp. strain ES6, under anaerobic, non-growth conditions in bicarbonate and PIPES buffers. Inorganic phosphate was released by cells during the experiments providing ligands for formation of insoluble U(VI) phosphates. Phosphate release was most probably the result of anaerobic hydrolysis of intracellular polyphosphates accumulated by ES6 during aerobic growth. Microbial reduction of U(VI) to U(IV) was also observed. However, the relative magnitudes of U(VI) removal by abiotic (phosphate-based) precipitation and microbial reduction depended on the buffer chemistry. In bicarbonate buffer, X-ray absorption fine structure (XAFS) spectroscopy showed that U in the solid phase was present primarily as a non-uraninite U(IV) phase, whereas in PIPES buffer, U precipitates consisted primarily of U(VI)-phosphate. In both bicarbonate and PIPES buffer, net release of cellular phosphate was measured to be lower than that observed in U-free controls suggesting simultaneous precipitation of U and PO3-4 . In PIPES, U(VI) phosphates formed a significant portion of U precipitates and mass balance estimates of U and P along with XAFS data corroborate this hypothesis. High-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) of samples from PIPES treatments indeed showedmore » both extracellular and intracellular accumulation of U solids with nanometer sized lath structures that contained U and P. In bicarbonate, however, more phosphate was removed than required to stoichiometrically balance the U(VI)/U(IV) fraction determined by XAFS, suggesting that U(IV) precipitated together with phosphate in this system. When anthraquinone-2,6-disulfonate (AQDS), a known electron shuttle, was added to the experimental reactors, the dominant removal mechanism in both buffers was reduction to a non-uraninite U(IV) phase. Uranium immobilization by abiotic precipitation or microbial reduction has been extensively reported; however, the present work suggests that strain ES6 can remove U(VI) from solution simultaneously through precipitation with phosphate ligands and microbial reduction, depending on the environmental conditions. Cellulomonadaceae are environmentally relevant subsurface bacteria and here, for the first time, the presence of multiple U immobilization mechanisms within one organism is reported using Cellulomonas sp. strain ES6.« less

Authors:
; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1009731
Report Number(s):
PNNL-SA-78187
Journal ID: ISSN 0006-3592; BIBIAU; 30457; KP1704020; TRN: US1101774
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Journal Name:
Biotechnology and Bioengineering, 108(2):264-276
Additional Journal Information:
Journal Volume: 108; Journal Issue: 2; Journal ID: ISSN 0006-3592
Country of Publication:
United States
Language:
English
Subject:
22 GENERAL STUDIES OF NUCLEAR REACTORS; ABSORPTION; ACID CARBONATES; AQUEOUS SOLUTIONS; BACTERIA; BUFFERS; CHEMISTRY; ELECTRONS; EXPERIMENTAL REACTORS; FINE STRUCTURE; HYDROLYSIS; HYPOTHESIS; MASS BALANCE; PHOSPHATES; PRECIPITATION; REMOVAL; SPECTROSCOPY; STRAINS; TRANSMISSION ELECTRON MICROSCOPY; URANIUM; X-RAY SPECTROSCOPY; U(VI); reduction; Cellulomonas; U(VI)-phosphate; bioremediation; XAFS; U(IV)-phosphate; Environmental Molecular Sciences Laboratory

Citation Formats

Sivaswamy, Vaideeswaran, Boyanov, Maxim I, Peyton, Brent M, Viamajala, Sridhar, Gerlach, Robin, Apel, William, Sani, Rajesh K, Dohnalkova, Alice, Kemner, Kenneth M, and Borch, Thomas. Multiple Mechanisms of Uranium Immobilization by Cellulomonas sp. Strain ES6. United States: N. p., 2011. Web. doi:10.1002/bit.22956.
Sivaswamy, Vaideeswaran, Boyanov, Maxim I, Peyton, Brent M, Viamajala, Sridhar, Gerlach, Robin, Apel, William, Sani, Rajesh K, Dohnalkova, Alice, Kemner, Kenneth M, & Borch, Thomas. Multiple Mechanisms of Uranium Immobilization by Cellulomonas sp. Strain ES6. United States. doi:10.1002/bit.22956.
Sivaswamy, Vaideeswaran, Boyanov, Maxim I, Peyton, Brent M, Viamajala, Sridhar, Gerlach, Robin, Apel, William, Sani, Rajesh K, Dohnalkova, Alice, Kemner, Kenneth M, and Borch, Thomas. Thu . "Multiple Mechanisms of Uranium Immobilization by Cellulomonas sp. Strain ES6". United States. doi:10.1002/bit.22956.
@article{osti_1009731,
title = {Multiple Mechanisms of Uranium Immobilization by Cellulomonas sp. Strain ES6},
author = {Sivaswamy, Vaideeswaran and Boyanov, Maxim I and Peyton, Brent M and Viamajala, Sridhar and Gerlach, Robin and Apel, William and Sani, Rajesh K and Dohnalkova, Alice and Kemner, Kenneth M and Borch, Thomas},
abstractNote = {Removal of hexavalent uranium (U(VI)) from aqueous solution was studied using a Gram-positive facultative anaerobe, Cellulomonas sp. strain ES6, under anaerobic, non-growth conditions in bicarbonate and PIPES buffers. Inorganic phosphate was released by cells during the experiments providing ligands for formation of insoluble U(VI) phosphates. Phosphate release was most probably the result of anaerobic hydrolysis of intracellular polyphosphates accumulated by ES6 during aerobic growth. Microbial reduction of U(VI) to U(IV) was also observed. However, the relative magnitudes of U(VI) removal by abiotic (phosphate-based) precipitation and microbial reduction depended on the buffer chemistry. In bicarbonate buffer, X-ray absorption fine structure (XAFS) spectroscopy showed that U in the solid phase was present primarily as a non-uraninite U(IV) phase, whereas in PIPES buffer, U precipitates consisted primarily of U(VI)-phosphate. In both bicarbonate and PIPES buffer, net release of cellular phosphate was measured to be lower than that observed in U-free controls suggesting simultaneous precipitation of U and PO3-4 . In PIPES, U(VI) phosphates formed a significant portion of U precipitates and mass balance estimates of U and P along with XAFS data corroborate this hypothesis. High-resolution transmission electron microscopy (HRTEM) and energy dispersive X-ray spectroscopy (EDS) of samples from PIPES treatments indeed showed both extracellular and intracellular accumulation of U solids with nanometer sized lath structures that contained U and P. In bicarbonate, however, more phosphate was removed than required to stoichiometrically balance the U(VI)/U(IV) fraction determined by XAFS, suggesting that U(IV) precipitated together with phosphate in this system. When anthraquinone-2,6-disulfonate (AQDS), a known electron shuttle, was added to the experimental reactors, the dominant removal mechanism in both buffers was reduction to a non-uraninite U(IV) phase. Uranium immobilization by abiotic precipitation or microbial reduction has been extensively reported; however, the present work suggests that strain ES6 can remove U(VI) from solution simultaneously through precipitation with phosphate ligands and microbial reduction, depending on the environmental conditions. Cellulomonadaceae are environmentally relevant subsurface bacteria and here, for the first time, the presence of multiple U immobilization mechanisms within one organism is reported using Cellulomonas sp. strain ES6.},
doi = {10.1002/bit.22956},
journal = {Biotechnology and Bioengineering, 108(2):264-276},
issn = {0006-3592},
number = 2,
volume = 108,
place = {United States},
year = {2011},
month = {2}
}