Multiple Mechanisms of Uranium Immobilization by Cellulomonas sp. strain ES6

• Published in: Biotechnology and bioengineering 2011-02, Vol.108 (2)
• Main Authors: Sivaswamy, Vaideeswaran, Brent Peyton, Viamajala, Sridhar, Robin Gerlach, William Apel, Rajesh Sani, Alice Dohnalkova, Thomas Borch
• Format: Article
• Language: English
• Subjects: BASIC BIOLOGICAL SCIENCES/GENOMICS/GENOME RESEARCH; bioremediation; Cellulomonas; U(VI) reduction; U(VI)-phosphate; Uranyl; XANES
• ISSN: 0006-3592; 1097-0290
• DOI: 10.1002/bit.22956

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 near edge structure (XANES) analysis showed U precipitates containing nearly equal fractions of U(IV) and U(VI), whereas in PIPES buffer, U precipitates consisted primarily of U(VI). Mass balance calculations for U and P corroborate these observations. High-resolution transmission electron microscopy (HR42TEM) and energy dispersive X-ray spectroscopy (EDS) showed both extracellular and intracellular accumulation of U solids. The U(VI)-phosphate precipitates, confirmed by EDS as containing U and P in equimolar concentrations, had nanometer sized lath structure. When anthraquinone-2,6-disulfonate (AQDS), a known electron shuttle, was added to the experimental reactors, U reduction became the dominant removal mechanism, in contrast to primarily phosphate-mediated precipitation observed in the absence of AQDS. Uranium immobilization by abiotic precipitation or microbial reduction has been extensively reported; however, 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, t 52 he presence of multiple U immobilization mechanisms within one organism is reported using Cellulomonas sp. strain ES6.