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.

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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.