Rhodococcus aetherivorans BCP1 as cell factory for the production of intracellular tellurium nanorods under aerobic conditions.

Background: Tellurite (TeO) is recognized as a toxic oxyanion to living organisms. However, mainly anaerobic or facultative-anaerobic microorganisms are able to tolerate and convert TeO into the less toxic and available form of elemental Tellurium (Te), producing Te-deposits or Te-nanostructures. The use of TeO-reducing bacteria can lead to the decontamination of polluted environments and the development of "green-synthesis" methods for the production of nanomaterials. In this study, the tolerance and the consumption of TeO have been investigated, along with the production and characterization of Te-nanorods by Rhodococcus aetherivorans BCP1 grown under aerobic conditions.

Results: Aerobically grown BCP1 cells showed high tolerance towards TeO with a minimal inhibitory concentration (MIC) of 2800 μg/mL (11.2 mM). TeO consumption has been evaluated exposing the BCP1 strain to either 100 or 500 μg/mL of KTeO (unconditioned growth) or after re-inoculation in fresh medium with new addition of KTeO (conditioned growth). A complete consumption of TeO at 100 μg/mL was observed under both growth conditions, although conditioned cells showed higher consumption rate. Unconditioned and conditioned BCP1 cells partially consumed TeO at 500 μg/mL. However, a greater TeO consumption was observed with conditioned cells. The production of intracellular, not aggregated and rod-shaped Te-nanostructures (TeNRs) was observed as a consequence of TeO reduction. Extracted TeNRs appear to be embedded in an organic surrounding material, as suggested by the chemical-physical characterization. Moreover, we observed longer TeNRs depending on either the concentration of precursor (100 or 500 μg/mL of KTeO) or the growth conditions (unconditioned or conditioned grown cells).

Conclusions: Rhodococcus aetherivorans BCP1 is able to tolerate high concentrations of TeO during its growth under aerobic conditions. Moreover, compared to unconditioned BCP1 cells, TeO conditioned cells showed a higher oxyanion consumption rate (for 100 μg/mL of KTeO) or to consume greater amount of TeO (for 500 μg/mL of KTeO). TeO consumption by BCP1 cells led to the production of intracellular and not aggregated TeNRs embedded in an organic surrounding material. The high resistance of BCP1 to TeO along with its ability to produce Te-nanostructures supports the application of this microorganism as a possible eco-friendly nanofactory.