Formation of selenium- and tellurium-containing nanoparticles during the growth of filamentous fungi

Microbial Se or Te reduction offers a potential route to biorecovery of these elements from solution. Reduction is often efficient and large amounts of these metalloids can be removed from solution, resulting in extensive precipitation around biomass. This is more effective than biomethylation, which can result in only small amounts of removal, and would necessitate a further trapping step to recover volatilized methylated derivatives. In this research, the fungi Aureobasidium pullulans, Mortierella humilis, Trichoderma harzianum, and Phoma glomeratawere used to investigate the formation of selenium- and tellurium-containing nanoparticles during growth on selenium- and tellurium-containing media. Most organisms were able to grow on both selenium- and tellurium-containing media at concentrations of 1 mM and this resulted in extensive precipitation of elemental selenium and tellurium on fungal surfaces observed by the bright red and black colour changes. Red or black deposits were confirmed as elemental selenium and tellurium, respectively, by X-ray powder diffraction. Apart from elemental selenium and tellurium, selenium oxide and tellurium oxide were also found after growth of Trichoderma harzianumin the presence of 1 mM selenite and tellurite together with the formation ofelemental selenium and tellurium. The hyphal matrix provided nucleation sites for metalloid deposition with extracellular protein and extracellular polymeric substances serving to localize the resultant Se or Te nanoparticles. These findings are relevant to remedial treatments for selenium and tellurium contamination, and possible novel approaches for selenium and tellurium biorecovery from liquid matrices.