Cloning, purification and characterization of Geobacillus stearothermophilus V uroporphyrinogen-III C-methyltransferase: evaluation of its role in resistance to potassium tellurite in Escherichia coli

Extreme Environments and High-Level Bacterial Tellurite Resistance

Bacteria have long been known to possess resistance to the highly toxic oxyanion tellurite, most commonly though reduction to elemental tellurium. However, the majority of research has focused on the impact of this compound on microbes, namely E. coli, which have a very low level of resistance. Very little has been done regarding bacteria on the other end of the spectrum, with three to four orders of magnitude greater resistance than E. coli. With more focus on ecologically-friendly methods of pollutant removal, the use of bacteria for tellurite remediation, and possibly recovery, further highlights the importance of better understanding the effect on microbes, and approaches for resistance/reduction. The goal of this review is to compile current research on bacterial tellurite resistance, with a focus on high-level resistance by bacteria inhabiting extreme environments.

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

Background

Tellurite (TeO₃²⁻) is recognized as a toxic oxyanion to living organisms. However, mainly anaerobic or facultative-anaerobic microorganisms are able to tolerate and convert TeO₃²⁻ into the less toxic and available form of elemental Tellurium (Te⁰), producing Te-deposits or Te-nanostructures. The use of TeO₃²⁻-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 TeO₃²⁻ 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 TeO₃²⁻ with a minimal inhibitory concentration (MIC) of 2800 μg/mL (11.2 mM). TeO₃²⁻ consumption has been evaluated exposing the BCP1 strain to either 100 or 500 μg/mL of K₂TeO₃ (unconditioned growth) or after re-inoculation in fresh medium with new addition of K₂TeO₃ (conditioned growth). A complete consumption of TeO₃²⁻ at 100 μg/mL was observed under both growth conditions, although conditioned cells showed higher consumption rate. Unconditioned and conditioned BCP1 cells partially consumed TeO₃²⁻ at 500 μg/mL. However, a greater TeO₃²⁻ consumption was observed with conditioned cells. The production of intracellular, not aggregated and rod-shaped Te-nanostructures (TeNRs) was observed as a consequence of TeO₃²⁻ 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 K₂TeO₃) or the growth conditions (unconditioned or conditioned grown cells).

Conclusions

Rhodococcus aetherivorans BCP1 is able to tolerate high concentrations of TeO₃²⁻ during its growth under aerobic conditions. Moreover, compared to unconditioned BCP1 cells, TeO₃²⁻conditioned cells showed a higher oxyanion consumption rate (for 100 μg/mL of K₂TeO₃) or to consume greater amount of TeO₃²⁻ (for 500 μg/mL of K₂TeO₃). TeO₃²⁻ 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 TeO₃²⁻ along with its ability to produce Te-nanostructures supports the application of this microorganism as a possible eco-friendly nanofactory.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-016-0602-8) contains supplementary material, which is available to authorized users.

Coupled selection of protein solubility in E. coli using uroporphyrinogen III methyltransferase as red fluorescent reporter

Uroporphyrinogen III methyltransferase (UMT) is a novel reporter owing to the catalytic products accumulated in cells emitting red florescence. Overexpression of UMT confers resistance of the Escherichia coli cells to potassium tellurite that inhibits cell growth. In this study, we applied UMT reporter for monitoring protein solubility of MBP or TEV protease variants under different expression conditions, as well as 12 maize proteins with either the designed linker or N-terminal SUMO tag. Effects of five enzymes involved in heme and siroheme biosynthesis on the reporter were also investigated. With increasing concentrations of potassium tellurite, colony numbers of the mixed cells expressing the selected five proteins with different solubility were decreased, but colonies displaying red fluorescence was identified to be produced the protein with relatively high solubility. The developed UMT reporter system is sensitive for monitoring protein solubility based on coupled fluorescence and chemical selection.