The tellurite resistance gene cluster of pathogenic bacteria and its effect on oxidative stress response

Tellurite resistance gene clusters have been identified in numerous pathogenic bacteria, including clinical isolates of Escherichia coli. The rareness of tellurium in host organisms and the noncontaminated environment raises a question about the true functionality of tellurite resistance gene clusters in pathogenesis and their possible contribution to bacterial fitness. The study aims to point out the beneficial effects of the tellurite resistance gene cluster of pathogenic bacteria to survive in ROS-rich environments. Here, we analysed the bacterial response to oxidative stress conditions with and without tellurite resistance gene clusters, which are composed of terWY1XY2Y3 and terZABCDEF genes. By measuring the levels of protein carbonylation, lipid peroxidation, and expression changes of oxidative stress genes upon oxidative stress, we propose a tellurite resistance gene cluster contribution to the elimination of oxidative damage, potentially increasing fitness and resistance to reactive oxygen species during macrophage attack. We have shown a different beneficial effect of various truncated versions of the tellurite resistance gene cluster on cell survival. The terBCDEF genes increased the survival of E. coli strain MC4100 by 13.21%, terW and terZABCDEF by 10.09%, and terWY1XY2Y3 and terZABCDEF by 25.57%, respectively. The ability to survive tellurite treatment is the most significant at 44.8% in wild clinical strain KL53 compared to laboratory strain E. coli MC4100 due to a complete wild-type plasmid presence.

Reduction of selenite and tellurite by a highly metal-tolerant marine bacterium

Selenium (Se) and tellurium (Te) contaminations in soils and water bodies have been widely reported in recent years. Se(IV) and Te(IV) were regarded as their most dangerous forms. Microbial treatments of Se(IV)- and Te(IV)-containing wastes are promising approaches because of their environmentally friendly and sustainable advantages. However, the salt-tolerant microbial resources that can be used for selenium/tellurium pollution control are still limited since industrial wastewaters usually contain a large number of salts. In this study, a marine Shewanella sp. FDA-1 (FDA-1) was reported for efficient Se(IV) and Te(IV) reduction under saline conditions. Process and product analyses were performed to investigate the bioreduction processes of Se(IV) and Te(IV). The results showed that FDA-1 can effectively reduce Se(IV) and Te(IV) to Se0 and Te0 Se(IV)/Te(IV) to Se0/Te0 in 72 h, which were further confirmed by XRD and XPS analyses. In addition, enzymatic and RT‒qPCR assays showed that flavin-related proteins, reductases, dehydrogenases, etc., could be involved in the bioreduction of Se(IV)/Te(IV). Overall, our results demonstrate the ability of FDA-1 to reduce high concentrations of Se(IV)/or Te(IV) to Se0/or Te0 under saline conditions and thus provide efficient microbial candidate for controlling Se and Te pollution.

Functional characterization of a TerC family protein of Riemerella anatipestifer in manganese detoxification and virulence

Manganese (Mn) is an essential element for bacteria, but the overload of manganese is toxic. In a previous study, we showed that the cation diffusion facilitator protein MetA and the resistance-nodulation-division efflux pump MetB are responsible for Mn efflux in the bacterial pathogen Riemerella anatipestifer CH-1. However, whether this bacterium encodes additional manganese efflux proteins is unclear. In this study, we show that R. anatipestifer CH-1 encodes a tellurium resistance C (TerC) family protein with low similarity to other characterized TerC family proteins. Compared to the wild type (WT), the terC mutant of R. anatipestifer CH-1 (∆terC) is sensitive to Mn(II) intoxication. The ability of TerC to export manganese is higher than that of MetB but lower than that of MetA. Consistently, terC deletion (∆terC) led to intracellular accumulation of Mn2+ under excess manganese conditions. Further study showed that ∆terC was more sensitive than the WT to the oxidant hypoclorite but not to hydrogen peroxide. Mutagenesis studies showed that the mutant at amino acid sites of Glu116 (E116), Asp122 (D122), Glu245 (E245) Asp248 (D248), and Asp254 (D254) may be involved in the ability of TerC to export manganese. The transcription of terC was upregulated under excess manganese and downregulated under iron-limited conditions. However, this was not dependent on the manganese metabolism regulator MetR. In contrast to a strain lacking the manganese efflux pump MetA or MetB, the terC mutant is attenuated in virulence in a duckling model of infection due to increased sensitivity to duck serum. Finally, comparative analysis showed that homologs of TerC are distributed across the bacterial kingdom, suggesting that TerC exerts a conserved manganese efflux function.IMPORTANCERiemerella anatipestifer is a notorious bacterial pathogen of ducks and other birds. In R. anatipestifer, the genes involved in manganese efflux have not been completely identified, although MetA and MetB have been identified as two manganese exporters. Additionally, the function of TerC family proteins in manganese efflux is controversial. Here, we demonstrated that a TerC family protein helps prevent Mn(II) intoxication in R. anatipestifer and that the ability of TerC to export manganese is intermediate compared to that of MetA and MetB. Sequence analysis and mutagenesis studies showed that the conserved key amino sites of TerC are Glu116, Asp122, Glu245, Asp248, and Asp254. The transcription of terC was regulated by manganese excess and iron limitation. Finally, we show that TerC plays a role in the virulence of R. anatipestifer due to the increased sensitivity to duck serum, rather than the increased sensitivity to manganese. Taken together, these results expand our understanding of manganese efflux and the pathogenic mechanisms of R. anatipestifer.

Investigation into the Antibacterial Mechanism of Biogenic Tellurium Nanoparticles and Precursor Tellurite

Antibacterial tellurium nanoparticles have the advantages of high activity and biocompatibility. Microbial synthesis of Te nanoparticles is not only a green technology but builds new ecological relationships in diverse environments. However, the antibacterial mechanism of Te nanoparticles is largely unclear. In this study, we report the bacterial synthesis of rod-shaped Te nanoparticles (BioTe) with high antibacterial activity against Escherichia coli. Morphology and permeability examination indicates that membrane damage is the primary reason for the antibacterial activity of BioTe, rather than ROS production and DNA damage. Moreover, a comparison of transcriptome and relative phenotypes reveals the difference in antibacterial mechanisms between BioTe and tellurite. Based on our evidence, we propose an antibacterial mode of rod-shaped BioTe, in which positively charged BioTe interact with the cell membrane through electrostatic attraction and then penetrate the membrane by using their sharp ends. In contrast, tellurite toxicity might be involved in sulfur metabolism.

Feasibility of simultaneous 99mTc-tetrofosmin and 123I-BMIPP dual-tracer imaging with cadmium-zinc-telluride detectors in patients undergoing primary coronary intervention for acute myocardial infarction

BACKGROUND

Simultaneous dual-tracer imaging using isotopes with close photo-peaks may benefit from improved properties of cadmium-zinc-telluride (CZT)-based scanners.

METHODS

Thirty patients having undergone primary percutaneous coronary intervention for acute myocardial infarction underwent single-(99mTc-tetrofosmin (TF) or 123I-BMIPP first) followed by simultaneous 99mTc-TF /123I-BMIPP dual-tracer imaging using a Discovery NM/CT 670 CZT. The values for the quantitative gated-SPECT (QGS) and the quantitative perfusion SPECT (QPS) were assessed.

RESULTS

The intra-class correlation (ICC) coefficients between the single- and dual-tracer imaging were high in all the QGS and QPS data (Summed motion score: 0.95, summed thickening score: 0.94, ejection fraction: 0.98, SRS for 99mTc-TF: 0.97/ for 123I-BMIPP: 0.95). Wall motion, wall thickening and rest scores per coronary-territory-based regions were also comparable between the single- and dual imaging (ICC coefficient > 0.91). The interrater concordance in the visual analysis for the infarction and perfusion-metabolism mismatch was significant for the global and regional left ventricle (P < 0.001).

CONCLUSION

The quantitative/semi-quantitative values for global and regional left-ventricular function, perfusion, and fatty acid metabolism were closely comparable between the dual-tracer imaging and the single-tracer mode. These data suggests the feasibility of the novel CZT-based scanner for the simultaneous 99mTc-TF /123I-BMIPP dual-tracer acquisitions in clinical settings.

Consequences of surface coatings and soil ageing on the toxicity of cadmium telluride quantum dots to the earthworm Eisenia fetida

The bioaccumulation potential and toxic effects of engineered nanomaterials (ENMs) to earthworms are poorly understood. Two studies were conducted following OECD TG 222 on Eisenia fetida to assess the effects of CdTe QDs with different coatings and soil ageing respectively. Earthworms were exposed to carboxylate (COOH), ammonium (NH₄⁺), or polyethylene glycol (PEG) coated CdTe QDs, or a micron scale (bulk) CdTe material, at nominal concentrations of 50, 500 and 2000 mg CdTe QD kg^-1 dry weight (dw) for 28 days in Lufa 2.2 soil. In the fresh soil study, earthworms accumulated similar amounts of Cd and Te in the CdTe-bulk exposures, while the accumulation of Cd was higher than Te during the exposures to CdTe QDs. However, neither the total Cd, nor Te concentrations in the earthworms, were easily explained by the extractable metal fractions in the soil or particle dissolution. There were no effects on survival, but some retardation of growth was observed at the higher doses. Inhibition of Na^+_/K⁺-ATPase activity with disturbances to tissue electrolytes, as well as tissue Cu and Mn were observed, but without depletion of total glutathione in the fresh soil experiment. Additionally, juvenile production was the most sensitive endpoint, with estimated nominal EC₅₀ of values >2000, 108, 65, 96 mg CdTe kg^-1 for bulk, PEG-, COOH- and NH₄⁺-coated CdTe QDs, respectively. In the aged soil study, the accumulation of Cd and Te was higher than in the fresh soil study in all CdTe QD exposures. Survival of the adult worms was reduced in the top CdTe-COOH and -NH₄⁺ QD exposures by 55 ± 5 and 60 ± 25%, respectively; and with decreases in growth. The nominal EC₅₀ values for juvenile production in the aged soil were 165, 88, 78 and 63 mg CdTe kg^-1 for bulk, PEG-, COOH- and NH₄⁺-coated CdTe QDs, respectively. In conclusion, exposure to nanoscale CdTe QDs, regardless of coating, caused more severe toxic effects that the CdTe bulk material and the toxicity increased after soil ageing. There were some coating-mediated effects, likely due to differences in the metal content and behaviour of the materials.

Nuclear Factor kappa B activation by Ag, Au nanoparticles, CdTe quantum dots or their binary mixtures in HepG2 cells

INTRODUCTION AND OBJECTIVE

Nuclear factor kappa B (NF-κB) signalling pathway plays a central role in the regulation of cellular response to stress. The aim of the study was to investigate the ability of silver nanoparticles (AgNPs), gold nanoparticles (AuNPs), CdTe quantum dots (CdTeQDs) or their binary mixtures to stimulate NF-κB binding in HepG2 cells. A dual luciferase reporter system was used to investigate NF-κB binding.

MATERIAL AND METHODS

Cells were transiently transfected with a firefly luciferase reporter system and Renilla luciferase expression plasmid as a transfection efficiency control. Twenty- four hours after transfection, the cells were treated with nanoparticles (10 μg/cm³ AgNPs, 10 μg/cm³ AuNPs, 3 μg/cm³ CdTeQDs) or with 10 ng/cm³ TNFα as a positive control. Six hours later, the cells were lysed and the activities of the luminescence of firefly and Renilla luciferases were measured using the Dual-Luciferase Reporter Assay System.

RESULTS

AuNPs and CdTeQDs alone significantly inhibited NF-κB binding activity. Co-treatment with AgNPs and CdTeQDs resulted in an additive effect, whereas the presence of AgNPs diminished the inhibitory effect of AuNPs. Interestingly, significant antagonism was observed between AuNPs and CdTeQDs, suggesting a similar mode of action.

CONCLUSIONS

Comparison of the NF-κB binding activity induced by the mixtures of NPs suggests that in some cases NF-κB binding activity might differ from that observed for the NPs alone.

Discovery of a Novel Gene Conferring Tellurite Tolerance Through Tellurite Reduction to Escherichia coli Transformant in Marine Sediment Metagenomic Library

Metagenomic library construction using a marine sediment-enrichment was employed in order to recover tellurium from tellurite, a tellurium oxyanion, dissolved in water and then functional screening was performed to discover a novel gene related to tellurite reduction. Transmission electron microscopy (TEM) revealed the formation of intracellular Te crystals in Escherichia coli cells transformed with a specific DNA fragment from the marine sediment metagenome. The metagenome fragment was composed of 691 bp and showed low homology to known proteins. Phylogenetic analysis suggested that the metagenome fragment was related to Pseudomonas stutzeri. Cloning and expression of an open reading frame (ORF) on the metagenome fragment validated the role of the fragment in conferring tellurite resistance and tellurite-reducing activity to E. coli host cells. E. coli transformant containing the ORF1 showed resistance to 1 mM Na₂TeO₃. The optimal tellurite-reducing activity of cells containing the ORF1 was recorded at 37 °C and pH 7.0.

Exploring the conformational changes in fibrinogen by forming protein corona with CdTe quantum dots and the related cytotoxicity

This study describes synthesis of N‑acetyl‑l‑cysteine-capped CdTe quantum dots (QDs) and investigates their interaction with plasma protein fibrinogen (FIB) and the structural changes of FIB. It is shown that the interaction of QDs with FIB is a spontaneous process and the major driving forces are van der Waals forces and hydrogen bonds. Multi-spectroscopic measurements show that the intrinsic fluorescence of FIB was quenched and secondary and tertiary structures were altered due to the interaction with QDs. In addition, the aggregation state of FIB was altered in the presence of QDs. Furthermore, the formed complexes of FIB with QDs reduced the cytotoxicity of QDs. The coating of FIB on QDs could lower intracellular QDs uptake and therefore result in less released cadmium ions and ROS productions. This study, therefore, might be helpful to the comprehensive understanding of QDs toxicity and provide evidence for assessing the safe application of nanoparticles.

TePhe, a tellurium-containing phenylalanine mimic, allows monitoring of protein synthesis in vivo with mass cytometry

Protein synthesis is central to maintaining cellular homeostasis and its study is critical to understanding the function and dysfunction of eukaryotic systems. Here we report L-2-tellurienylalanine (TePhe) as a noncanonical amino acid for direct measurement of protein synthesis. TePhe is synthetically accessible, nontoxic, stable under biological conditions, and the tellurium atom allows its direct detection with mass cytometry, without postexperiment labeling. TePhe labeling is competitive with phenylalanine but not other large and aromatic amino acids, demonstrating its molecular specificity as a phenylalanine mimic; labeling is also abrogated in vitro and in vivo by the protein synthesis inhibitor cycloheximide, validating TePhe as a translation reporter. In vivo, imaging mass cytometry with TePhe visualizes translation dynamics in the mouse gut, brain, and tumor. The strong performance of TePhe as a probe for protein synthesis, coupled with the operational simplicity of its use, suggests TePhe could become a broadly applied molecule for measuring translation in vitro and in vivo.

Formation of nanoscale Te0 and its effect on TeO32- reduction in CH4-based membrane biofilm reactor

Formation and recovery of elemental tellurium (Te⁰) from wastewaters are required by increasing demands and scarce resources. Membrane biofilm reactor (MBfR) using gaseous electron donor has been reported as a low-cost and benign technique to reduce and recover metal (loids). In this study, we demonstrate the feasibility of nanoscale Te⁰ formation by tellurite (TeO₃^2-) reduction in a CH₄-based MBfR. Biogenic Te⁰ intensively attached on cell surface, within diameters ranging from 10 nm to 30 nm and the hexagonal nanostructure. Along with the Te⁰ formation, the TeO₃^2- reduction was inhibited. After flushing, biofilm resumed the TeO₃^2- reduction ability, suggesting that the formed nanoscale Te⁰ might inhibit the reduction by hindering substrate transfer of TeO₃^2- to microbes. The 16S rRNA gene amplicon sequencing revealed that Thermomonas and Hyphomicrobium were possibly responsible for TeO₃^2- reduction since they increased consecutively along with the experiment operation. The PICRUSt (Phylogenetic Investigation of Communities by Reconstruction of Unobserved States) analysis showed that the sulfite reductases were positively correlated with the TeO₃^2- flux, indicating they were potential enzymes involved in reduction process. This study confirms the capability of CH₄-based MBfR in tellurium reduction and formation, and provides more techniques for resources recovery and recycles.

Morphology-tunable tellurium nanomaterials produced by the tellurite-reducing bacterium Lysinibacillus sp. ZYM-1

Although tellurite is highly toxic to organisms, elemental tellurium nanomaterials (TeNMs) have many uses. The microbe-mediated reduction of tellurite to Te(0) has been shown to be a green and cost-effective approach for turning waste into wealth. However, it is difficult to tune the morphology of biogenic nanomaterials. In this study, a series of experiments was conducted to investigate the factors influencing tellurite reduction by the tellurite-reducing bacterium Lysinibacillus sp. ZYM-1, including pH, tellurite concentration, temperature, and heavy metal ions. The optimal removal efficiency of tellurite was respectively achieved at pH 8, 0.5 mM tellurite, and 40 °C. All of the tested metal ions retarded the reduction of tellurite, especially Cd²⁺ and Co²⁺, which completely inhibited its reduction. Further characterization of the biogenic TeNMs indicated that their morphology could be tuned by the tellurite concentration, pH, temperature, and organic solvents used. Regular Te nanosheets were produced using 5 mM tellurite. The TeNMs were primarily synthesized in the cell membrane. Hexagonal Te nanoplates, nanorods, nanoflowers, and nanobranches were synthesized when combining membrane fractions with tellurite and NADH. The diverse morphologies are assumed to be induced by the synergy between the reduction kinetics and the protein structure. Therefore, this study confirmed that the bacterium can tune the morphology of TeNMs, broadening the potential application of biogenic TeNMs.

Total content and in vitro bioaccessibility of tellurium in Brazil nuts

Alongside the Brazil nut's role as an excellent source of vitamins, oil, fatty acids, lipids and nutrients, it is also recognized as a rich source of selenium. The pathway along which selenium and sulfur are metabolized in plants is theorized to be the same as that used for tellurium. Total tellurium content and its bioaccessibility are then evaluated by ICP-MS. Interferences and sample preparation are evaluated for the accurate determination of tellurium, and the accuracy determined through analysis of the certified reference material 1643e. A concentration of 4.02 ± 0.391 ng g^-1 is obtained as an average concentration through external and internal calibrations. Through this reliable result, tellurium bioaccessibility in Brazil nuts is obtained via an in vitro validated unified bioaccessibility method. Values of 32% and 30% of total tellurium are available in the gastric and gastrointestinal fractions, respectively.

Tellurate enters Escherichia coli K-12 cells via the SulT-type sulfate transporter CysPUWA

Soluble forms of tellurium are environmental contaminants that are toxic to microorganisms. While tellurite [Te(IV)] is a well-characterized antimicrobial agent, little is known about the interactions of tellurate [Te(VI)] with bacterial cells. In this study, we investigated the role of sulfate transporters in the uptake of tellurate in Escherichia coli K-12. Mutant strains carrying a deletion of the cysW gene in the CysPUWA sulfate transporter system accumulated less cellular tellurium and exhibited higher resistance to tellurate compared with the wild-type strain. Complementation of the mutation restored tellurate sensitivity and uptake. These results indicate that tellurate enters E. coli cells to cause toxic effects via the CysPUWA sulfate transporter.

Characterization of a Novel Porin-Like Protein, ExtI, from Geobacter sulfurreducens and Its Implication in the Reduction of Selenite and Tellurite

The extI gene in Geobacter sulfurreducens encodes a putative outer membrane channel porin, which resides within a cluster of extHIJKLMNOPQS genes. This cluster is highly conserved across the Geobacteraceae and includes multiple putative c-type cytochromes. In silico analyses of the ExtI sequence, together with Western blot analysis and proteinase protection assays, showed that it is an outer membrane protein. The expression level of ExtI did not respond to changes in osmolality and phosphate starvation. An extI-deficient mutant did not show any significant impact on fumarate or Fe(III) citrate reduction or sensitivity to β-lactam antibiotics, as compared with those of the wild-type strain. However, extI deficiency resulted in a decreased ability to reduce selenite and tellurite. Heme staining analysis revealed that extI deficiency affects certain heme-containing proteins in the outer and inner membranes, which may cause a decrease in the ability to reduce selenite and tellurite. Based on these observations, we discuss possible roles for ExtI in selenite and tellurite reduction in G. sulfurreducens.

Comparative investigation of toxicity and bioaccumulation of Cd-based quantum dots and Cd salt in freshwater plant Lemna minor L

The purpose of this study was to determine the toxicity of two different sources of cadmium, i.e. CdCl₂ and Cd-based Quantum Dots (QDs), for freshwater model plant Lemna minor L. Cadmium telluride QDs were capped with two coating ligands: glutathione (GSH) or 3-mercaptopropionic acid (MPA). Growth rate inhibition and final biomass inhibition of L. minor after 168-h exposure were monitored as toxicity endpoints. Dose-response curves for Cd toxicity and EC50_168h values were statistically evaluated for all sources of Cd to uncover possible differences among the toxicities of tested compounds. Total Cd content and its bioaccumulation factors (BAFs) in L. minor after the exposure period were also determined to distinguish Cd bioaccumulation patterns with respect to different test compounds. Laser-Induced Breakdown Spectroscopy (LIBS) with lateral resolution of 200µm was employed in order to obtain two-dimensional maps of Cd spatial distribution in L. minor fronds. Our results show that GSH- and MPA-capped Cd-based QDs have similar toxicity for L. minor, but are significantly less toxic than CdCl₂. However, both sources of Cd lead to similar patterns of Cd bioaccumulation and distribution in L. minor fronds. Our results are in line with previous reports that the main mediators of Cd toxicity and bioaccumulation in aquatic plants are Cd²⁺ ions dissolved from Cd-based QDs.

Two distinct periplasmic enzymes are responsible for tellurite/tellurate and selenite reduction by strain ER-Te-48 associated with the deep sea hydrothermal vent tube worms at the Juan de Fuca Ridge black smokers

Strain ER-Te-48 isolated from a deep-ocean hydrothermal vent tube worm is capable of resisting and reducing extremely high levels of tellurite, tellurate, and selenite, which are used for respiration anaerobically. Tellurite and tellurate reduction is accomplished by a periplasmic enzyme of 215 kDa comprised of 3 subunits (74, 42, and 25 kDa) in a 2:1:1 ratio. The optimum pH and temperature for activity is 8.0 and 35 °C, respectively. Tellurite reduction has a V _max of 5.6 µmol/min/mg protein and a K _m of 3.9 mM. In the case of the tellurate reaction, V _max and K _m were 2.6 µmol/min/mg protein and 2.6 mM, respectively. Selenite reduction is carried out by another periplasmic enzyme with a V _max of 2.8 µmol/min/mg protein, K _m of 12.1 mM, and maximal activity at pH 6.0 and 38 °C. This protein is 165 kDa and comprised of 3 subunits of 98, 44, and 23 kDa in a 1:1:1 ratio.

Rhizopus stolonifer mediated biosynthesis of biocompatible cadmium chalcogenide quantum dots

We report an efficient method to biosynthesize biocompatible cadmium telluride and cadmium sulphide quantum dots from the fungus Rhizopus stolonifer. The suspension of the quantum dots exhibited purple and greenish-blue luminescence respectively upon UV light illumination. Photoluminescence spectroscopy, X-ray diffraction, and transmission electron microscopy confirms the formation of the quantum dots. From the photoluminescence spectrum the emission maxima is found to be 424 and 476nm respectively. The X-ray diffraction of the quantum dots matches with results reported in literature. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay for cell viability evaluation carried out on 3-days transfer, inoculum 3×10⁵ cells, embryonic fibroblast cells lines shows that more than 80% of the cells are viable even after 48h, indicating the biocompatible nature of the quantum dots. A good contrast in imaging has been obtained upon incorporating the quantum dots in human breast adenocarcinoma Michigan Cancer Foundation-7 cell lines.

Interaction of TGA@CdTe Quantum Dots with an Extracellular Matrix of Haematococcus pluvialis Microalgae Detected Using Surface-Enhanced Raman Spectroscopy (SERS)

The present study reports the localization and interaction of thioglycolic acid (TGA) capped CdTe quantum dots (TGA@CdTe QDs) within the extracellular matrix (ECM) of Haematococcus pluvialis (Chlorophyceae) microalgae (HPM) after an incubation period of 5 min. Changes in the Raman spectrum of HPM induced by the adsorption of the TGA@CdTe QDs are successfully found by using naked gold anisotropic structures as nano-sensors for surface-enhanced Raman scattering (SERS effect). Raman spectroscopy results show that TGA@CdTe QDs interact with the biomolecules present in the ECM. Sample preparation and characterization by complementary techniques such as confocal and electron microscopy are also used to confirm the presence and localization of the nanoparticles in the algae. This research shows new evidence on early accumulation of QDs in plant cells and would further improve our understanding about their environmental impact.

Extracellular production of tellurium nanoparticles by the photosynthetic bacterium Rhodobacter capsulatus

The toxic oxyanion tellurite (TeO3(2-)) is acquired by cells of Rhodobacter capsulatus grown anaerobically in the light, via acetate permease ActP2 and then reduced to Te(0) in the cytoplasm as needle-like black precipitates. Interestingly, photosynthetic cultures of R. capsulatus can also generate Te(0) nanoprecipitates (TeNPs) outside the cells upon addition of the redox mediator lawsone (2-hydroxy-1,4-naphtoquinone). TeNPs generation kinetics were monitored to define the optimal conditions to produce TeNPs as a function of various carbon sources and lawsone concentration. We report that growing cultures over a 10 days period with daily additions of 1mM tellurite led to the accumulation in the growth medium of TeNPs with dimensions from 200 up to 600-700 nm in length as determined by atomic force microscopy (AFM). This result suggests that nucleation of TeNPs takes place over the entire cell growth period although the addition of new tellurium Te(0) to pre-formed TeNPs is the main strategy used by R. capsulatus to generate TeNPs outside the cells. Finally, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FT-IR) analysis of TeNPs indicate they are coated with an organic material which keeps the particles in solution in aqueous solvents.

Assessment of commercial chromogenic solid media for the detection of non-O157 Shiga toxin-producing Escherichia coli (STEC)

Detection of Shiga toxin-producing Escherichia coli (STEC) has evolved significantly since the introduction of sorbitol-MacConkey agar. This study compares four chromogenic media (CHROMagar™ STEC, Rainbow® O157 agar, CHROMagar™ O157, and Colorex® O157) in their identification of non-O157 STEC. When 161 non-O157 STEC were directly inoculated onto each medium, detection rates on CHROMagar™ STEC, Rainbow® O157 agar, CHROMagar™ O157 and Colorex® O157 were 90%, 70%, 3.7% and 6.8%, respectively. Tellurite minimal inhibitory concentrations (MICs) correlated with growth on CHROMagar™ STEC as 20 of 22 isolates with poor or no growth had MICs ≤1μg/mL. Stool spiking experiments revealed that CHROMagar™ STEC had the highest recovery of the six most common non-O157 STEC, ranging from 30% (in mucoid stool) to 98% (in watery stool). When using clinical stool samples, CHROMagar™ STEC had a sensitivity, specificity, positive predictive value, and negative predictive value of 84.6%, 87%, 13.9%, and 99.6%, respectively.

Apoptosis Induction and Imaging of Cadmium-Telluride Quantum Dots with Wogonin in Multidrug-Resistant Leukemia K562/A02 Cell

Wogonin (5,7-dihydroxy-8-methoxyflavone) is one of the active components of flavonoids isolated from Scutellariae radix and possesses antitumor effect against leukemia. Cadmium-telluride quantum dots (CdTe-QDs) are a kind of nanoparticles with great potential in functioning as an efficient drug delivery vector in biomedical research. In this study, we investigated the synergistic effect of CdTe-QDs with Wogonin on the induction of apoptosis using drug-resistant human leukemia KA cells. Flow cytometry analysis, assay of morphology under electron microscope, quantitative analysis of tumor volume and micro-CT imaging demonstrated that compared with that by pure CdTe-QDs or wogonin, the apoptosis rate increased sharply when treated wirh CdTe-QDs together with wogonin on KA cells. These results proved that the nanocomposites readily overcame the barrier of drug-resistance and provoked cell apoptosis in vitro and in vivo by facilitating the interaction between wogonin and KA cells. As known to all, it is an inevitable tendency that new effective therapies will take the place of conventional chemotherapy and radiotherapy presenting significant disadvantages. According to this article, CdTe-QD combined with wogonin is a possible alternative for some cancer treatments.

Anti-bacterial TeNPs biosynthesized by haloarcheaon Halococcus salifodinae BK3

Microbial synthesis of highly structured metal sulfide and metallic nanoparticles is a benign approach of nanomaterial synthesis. Various microbes have been exploited for nanoparticle synthesis, but nanofabrication using haloarchaea is still in nascent stages. Here, we report the intracellular synthesis of hexagonal needle-shaped tellurium nanoparticles with an aspect ratio of 1:4.4, by the haloarcheon Halococcus salifodinae BK3. The isolate was able to tolerate up to 5.5 mM K2TeO3. The yield of tellurium nanoparticles was highest when the culture was exposed to 3 mM K2TeO3, even though the isolate exhibited slightly decreased growth rate as compared to the culture growing in the absence of K2TeO3. The enzyme tellurite reductase was responsible for tellurite resistance and nanoparticle synthesis in H. salifodinae BK3. These tellurium nanoparticles exhibited anti-bacterial activities against both Gram-positive and Gram-negative bacteria, with higher antibacterial activity towards Gram-negative bacteria. This is the first report on the synthesis of tellurium nanoparticles by Halophilic archaea.

Escherichia coli 6-phosphogluconate dehydrogenase aids in tellurite resistance by reducing the toxicant in a NADPH-dependent manner

Exposure to the tellurium oxyanion tellurite (TeO3(2-)) results in the establishment of an oxidative stress status in most microorganisms. Usually, bacteria growing in the presence of the toxicant turn black because of the reduction of tellurite (Te(4+)) to the less-toxic elemental tellurium (Te(0)). In vitro, at least part of tellurite reduction occurs enzymatically in a nicotinamide dinucleotide-dependent reaction. In this work, we show that TeO3(2-) reduction by crude extracts of Escherichia coli overexpressing the zwf gene (encoding glucose-6-phosphate dehydrogenase) takes place preferentially in the presence of NADPH instead of NADH. The enzyme responsible for toxicant reduction was identified as 6-phosphogluconate dehydrogenase (Gnd). The gnd gene showed a subtle induction at short times after toxicant exposure while strains lacking gnd were more susceptible to the toxicant. These results suggest that both NADPH-generating enzymes from the pentose phosphate shunt may be involved in tellurite detoxification and resistance in E. coli.

Characterization of the interaction of FTO protein with thioglycolic acid capped CdTe quantum dots and its analytical application

CdTe quantum dots (QDs) were synthesized in aqueous solution using thioglycolic acid (TGA) as stabilizing agents. The interaction between TGA-CdTe QDs and fat mass and obesity-associated (FTO) protein was investigated by fluorescence, UV-visible absorption, synchronous fluorescence and three-dimensional fluorescence spectroscopy. Results revealed that TGA-CdTe QDs could strongly quench the intrinsic fluorescence of FTO protein with a static quenching procedure. Both the van der Waals and hydrogen bonding played a major role in stabilizing the complex. The binding constant and thermodynamic parameters at different temperatures were obtained. In addition, we found that the fluorescence intensity of QDs was significantly enhanced by the addition of FTO protein. Based on this, a sensitive method for detecting FTO protein was obtained in the linear range of 5.52×10(-9)-6.62×10(-7) mol L(-1) with the detection limit of 1.14×10(-9) mol L(-1). The influences of factors on the interaction between FTO protein and TGA-CdTe QDs were studied.