Thorium is a ubiquitous radioactive element used in manufacturing and as a fuel for
nuclear reactors. The most common thorium isotope, 232Th,
decays to radium and radon and has a half-life of 14 X 109 years (ToxFAQs: Thorium). Research
exploring microbial interactions with thorium has focused on the immobilization of soluble
thorium through bioprecipitation, biosorption, and bioaccumulation.
When exposed to Th4+, Bradyrhizobium and Sinorhizobium
strains secreted extracellular polymers in which the thorium ions were
precipitated (Santamaria et al, 2003).
A similar response was observed during exposure to Al3+ and
may represent a mechanism of metal tolerance. Yong and Macaskie (1998) demonstrated
a system in which thorium and lanthanum ions were precipitated in a complex with
phosphate liberated by phosphatase activity expressed in a Citrobacter sp.
Thorium accumulated by Saccharomyces cerevisiae cells was localized in
vacuoles, the cytoplasm, and cell walls at levels dependent on the stage of growth
(Gadd and White, 1989). Mycobacterium smegmatis cells were found to preferentially
bind thorium ions in a mixture of thorium, uranyl, and lanthanum ions (Andres et al,
1995). Thorium biosorption by biomass of various other
bacteria (Hirose and Tanoue, 2001)
and fungi (White and Gadd, 1990) has been described.
For more information:
Medline for thorium AND bacteria
Andres Y, MacCordick HJ, Hubert JC. Selective biosorption of thorium ions by an immobilized
mycobacterial biomass. Appl Microbiol Biotechnol. 1995;44:271-276.
Gadd GM, White C. Uptake and intracellular compartmentation of thorium in
Saccharomyces cerevisiae. Environ Pollut. 1989;61:187-97.
Yong P, Macaskie LE. Bioaccumulation of lanthanum, uranium, and thorium, and use of a model system to develop a method for the biologically-mediated removal of plutonium from solution. J Chem Technol Biotechnol. 1998;71:15-26.