The wide anthropogenic use of selenium compounds represents the major source of selenium pollution worldwide, causing environmental issues and health concerns. Microbe-based strategies for metal removal/recovery have received increasing interest thanks to the association of the microbial ability to detoxify toxic metal/metalloid polluted environments with the production of nanomaterials. This study investigates the tolerance and the bioconversion of selenite (SeO) by the aerobically grown Actinomycete Rhodococcus aetherivorans BCP1 in association with its ability to produce selenium nanoparticles and nanorods (SeNPs and SeNRs). The BCP1 strain showed high tolerance towards SeO with a Minimal Inhibitory Concentration (MIC) of 500mM. The bioconversion of SeO was evaluated considering two different physiological states of the BCP1 strain, i.e. unconditioned and/or conditioned cells, which correspond to cells exposed for the first time or after re-inoculation in fresh medium to either 0.5 or 2mM of NaSeO, respectively. SeO bioconversion was higher for conditioned grown cells compared to the unconditioned ones. Selenium nanostructures appeared polydisperse and not aggregated, as detected by electron microscopy, being embedded in an organic coating likely responsible for their stability, as suggested by the physical-chemical characterization. The production of smaller and/or larger SeNPs was influenced by the initial concentration of provided precursor, which resulted in the growth of longer and/or shorter SeNRs, respectively. The strong ability to tolerate high SeO concentrations coupled with SeNP and SeNR biosynthesis highlights promising new applications of Rhodococcus aetherivorans BCP1 as cell factory to produce stable Se-nanostructures, whose suitability might be exploited for biotechnology purposes.

BackgroundTellurite (TeO3 2−) is recognized as a toxic oxyanion to living organisms. However, mainly anaerobic or facultative-anaerobic microorganisms are able to tolerate and convert TeO3 2− into the less toxic and available form of elemental Tellurium (Te0), producing Te-deposits or Te-nanostructures. The use of TeO3 2−-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 TeO3 2− have been investigated, along with the production and characterization of Te-nanorods by Rhodococcus aetherivorans BCP1 grown under aerobic conditions.ResultsAerobically grown BCP1 cells showed high tolerance towards TeO3 2− with a minimal inhibitory concentration (MIC) of 2800 μg/mL (11.2 mM). TeO3 2− 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 TeO3 2− at 100 μg/mL was observed under both growth conditions, although conditioned cells showed higher consumption rate. Unconditioned and conditioned BCP1 cells partially consumed TeO3 2− at 500 μg/mL. However, a greater TeO3 2− consumption was observed with conditioned cells. The production of intracellular, not aggregated and rod-shaped Te-nanostructures (TeNRs) was observed as a consequence of TeO3 2− 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 TeO3 2− during its growth under aerobic conditions. Moreover, compared to unconditioned BCP1 cells, TeO3 2− conditioned cells showed a higher oxyanion consumption rate (for 100 μg/mL of K2TeO3) or to consume greater amount of TeO3 2− (for 500 μg/mL of K2TeO3). TeO3 2− 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 TeO3 2− along with its ability to produce Te-nanostructures supports the application of this microorganism as a possible eco-friendly nanofactory.Electronic supplementary materialThe online version of this article (doi:10.1186/s12934-016-0602-8) contains supplementary material, which is available to authorized users.

Tellurite (TeO32−) is a hazardous and toxic oxyanion for living organisms. However, several microorganisms can bioconvert TeO32− into the less toxic form of elemental tellurium (Te0). Here, Rhodococcus aetherivorans BCP1 resting (non-growing) cells showed the proficiency to produce tellurium-based nanoparticles (NPs) and nanorods (NRs) through the bioconversion of TeO32−, depending on the oxyanion initial concentration and time of cellular incubation. Te-nanostructures initially appeared in the cytoplasm of BCP1 cells as spherical NPs, which, as the exposure time increased, were converted into NRs. This observation suggested the existence of an intracellular mechanism of TeNRs assembly and growth that resembled the chemical surfactant-assisted process for NRs synthesis. The TeNRs produced by the BCP1 strain showed an average length (>700 nm) almost doubled compared to those observed in other studies. Further, the biogenic TeNRs displayed a regular single-crystalline structure typically obtained for those chemically synthesized. The chemical-physical characterization of the biogenic TeNRs reflected their thermodynamic stability that is likely derived from amphiphilic biomolecules present in the organic layer surrounding the NRs. Finally, the biogenic TeNRs extract showed good electrical conductivity. Thus, these findings support the suitability of this strain as eco-friendly biocatalyst to produce high quality tellurium-based nanomaterials exploitable for technological purposes.

Gadolinium (Gd)-containing chelates have been established as diagnostics tools. However, extensive use in magnetic resonance imaging has led to increased Gd levels in industrialized parts of the world, adding to natural occurrence and causing environmental and health concerns. A vast amount of data shows that metal may accumulate in the human body and its deposition has been detected in organs such as brain and liver. Moreover, the disease nephrogenic systemic fibrosis has been linked to increased Gd3+ levels. Investigation of Gd3+ effects at the cellular and molecular levels mostly revolves around calcium-dependent proteins, since Gd3+ competes with calcium due to their similar size; other reports focus on interaction of Gd3+ with nucleic acids and carbohydrates. However, little is known about Gd3+ effects on membranes; yet some results suggest that Gd3+ interacts strongly with biologically-relevant lipids (e.g., brain membrane constituents) and causes serious structural changes including enhanced membrane rigidity and propensity for lipid fusion and aggregation at much lower concentrations than other ions, both toxic and essential. This review surveys the impact of the anthropogenic use of Gd emphasizing health risks and discussing debilitating effects of Gd3+ on cell membrane organization that may lead to deleterious health consequences.

There has been an increasing interest in the potential of nanomedicine, particularly in the use of nanoparticles between 10 nm and 1 μm in diameter as drug delivery vehicles. For pulmonary drug delivery, it is important to understand the effect of polymeric nanoparticles on the lung surfactant in order to optimize the carriers by reducing their potential toxicological effects. This work presents a biophysical study of the impact of gelatin nanoparticles on packing and lateral organization of simple and complex lipid layers containing the major components of lung surfactant. Zwitterionic phosphatidylcholines, negatively charged phosphatidylglycerols, and the sterol cholesterol were employed in the models. In addition, the impact of acyl chain length was investigated. Packing was determined by surface pressure-area isotherms, whereas direct imaging of the surfactant at the air-water interface was performed using Brewster angle microscopy. Our results indicate minor changes in the surface pressure-area isotherms but concomitantly significant effects on the lateral organization of the monolayers upon nanoparticle addition. The data also suggest differential interactions of nanoparticles with the major lipid classes. Gelatin nanoparticles interact stronger with negatively charged phosphatidyl-glycerols compared to zwitterionic phosphatidyl-cholines. Furthermore, charge distribution depending on the molar lipid ratio and acyl chain saturation is important as well. Even cholesterol, whose concentration is low compared to other components, plays an important role in nanoparticle interactions.