Formation of biogenic tellurium nanorods in unicellular green alga Chlamydomonas reinhardtii.

Tellurium (Te) is an industrially useful element but causes environmental contamination. The formation of biogenic Te nanorods (Te-BgNRs) in plants is one of the Te detoxification pathways associated with the phytoremediation of Te because Te-BgNRs contain low-toxicity Te at high densities. In this study, we investigated the mechanism of Te-BgNR formation in a common unicellular green alga, Chlamydomonas reinhardtii, on the basis of elemental analysis by inductively coupled plasma mass spectrometry (ICP-MS). After exposure to 1000 μM sodium tellurate (Na2TeO4) for 2 weeks, the alga accumulated 65.2 fg of Te per cell, and 55.8% of which was present in an insoluble form. Electron microscopic observations revealed that the insoluble Te was rod-shaped elemental Te, i.e. Te-BgNRs, and had a highly crystalline nanostructure. We determined the Te contents in Te-BgNRs by single-particle ICP-MS analysis and found that these nanorods were formed at tellurate exposure concentrations of 100 to 1000 μM. In contrast, soluble Te compounds were found in algal cells even at exposure concentrations lower than 100 μM. These findings suggest that the algal cells initially metabolized tellurate to form soluble Te compounds, and excess tellurate that could not be metabolized was then transformed to Te-BgNRs, which are less toxic than tellurate. Our findings provide a novel approach to Te remediation through the formation of BgNRs in C. reinhardtii.