Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1 were isolated from the rhizosphere soil of the selenium-hyperaccumulator legume Astragalus bisulcatus and waste material from a dumping site for roasted pyrites, respectively. Here, these bacterial strains were studied as cell factories to generate selenium-nanostructures (SeNS) under metabolically controlled growth conditions. Thus, a defined medium (DM) containing either glucose or pyruvate as carbon and energy source along with selenite () was tested to evaluate bacterial growth, oxyanion bioconversion and changes occurring in SeNS features with respect to those generated by these strains grown on rich media. Transmission electron microscopy (TEM) images show extra- or intra-cellular emergence of SeNS in SeITE02 or MPV1 respectively, revealing the presence of two distinct biological routes of SeNS biogenesis. Indeed, the stress exerted by upon SeITE02 cells triggered the production of membrane vesicles (MVs), which surrounded Se-nanoparticles (SeNPsSeITE02-G_e and SeNPsSeITE02-P_e with average diameter of 179 ± 56 and 208 ± 60 nm, respectively), as highlighted by TEM and scanning electron microscopy (SEM), strongly suggesting that MVs might play a crucial role in the excreting mechanism of the SeNPs in the extracellular environment. On the other hand, MPV1 strain biosynthesized intracellular inclusions likely containing hydrophobic storage compounds and SeNPs (123 ± 32 nm) under pyruvate conditioning, while the growth on glucose as the only source of carbon and energy led to the production of a mixed population of intracellular SeNPs (118 ± 36 nm) and nanorods (SeNRs; average length of 324 ± 89). SEM, fluorescence spectroscopy, and confocal laser scanning microscopy (CLSM) revealed that the biogenic SeNS were enclosed in an organic material containing proteins and amphiphilic molecules, possibly responsible for the high thermodynamic stability of these nanomaterials. Finally, the biogenic SeNS extracts were photoluminescent upon excitation ranging from 380 to 530 nm, whose degree of fluorescence emission (λem = 416-640 nm) was comparable to that from chemically synthesized SeNPs with L-cysteine (L-cys SeNPs). This study offers novel insights into the formation, localization, and release of biogenic SeNS generated by two different Gram-negative bacterial strains under aerobic and metabolically controlled growth conditions. The work strengthens the possibility of using these bacterial isolates as eco-friendly biocatalysts to produce high quality SeNS targeted to possible biomedical applications and other biotechnological purposes.

Physical-Chemical Properties of Biogenic Selenium Nanostructures Produced by Stenotrophomonas maltophilia SeITE02 and Ochrobactrum sp. MPV1.

Especially in the last decade, a vast number of papers on Se and its role in health issues have been published. This review gives a brief, critical overview of the main analytical findings reported in these papers. Of particular interest is the Se content in different food sources worldwide and the extent to which their consumption is reflected in the Se content of human tissues and body fluids. Several food sources, both natural (Brazil nuts, garlic, Brassica juncea) and Se-enriched (yeast-based supplements), are discussed as to origin, characteristics, Se metabolism and impact of their consumption on the human body. The continuous development of new and improvement of existing analytical techniques has provided different powerful tools to unravel the Se species and their function. An up-to-date literature study on Se speciation analysis is given, illustrating how analytical chemistry in its different facets aids in the identification of Se compounds and provides insight into the complete metabolic pathway of Se throughout the human body. This review includes a detailed image of the current state-of-the-art of Se speciation analysis in these food sources and in human tissues and body fluids.

Selenium speciation from food source to metabolites: a critical review.

The recent developments in analytical techniques capable of providing information on the identity and quantity of heteroatom-containing biomolecules are critically discussed. Particular attention is paid to the emerging areas of bioinorganic analysis including: (i) a comprehensive analysis of the entirety of metal and metalloid species within a cell or tissue type (metallomics), (ii) the study of the part of the metallome involving the protein ligands (metalloproteomics), and (iii) the use of a heteroelement, naturally present in a protein or introduced in a tag added by means of derivatisation, for the spotting and quantification of proteins (heteroatom-tagged proteomics). Inductively coupled plasma mass spectrometry (ICP MS), used as detector in chromatography and electrophoresis, and supported by electrospray and MALDI MS, appears as the linchpin analytical technique for these emerging areas. This review focuses on the recent advances in ICP MS in biological speciation analysis including sensitive detection of non-metals, especially of sulfur and phosphorus, couplings to capillary and nanoflow HPLC and capillary electrophoresis, laser ablation ICP MS detection of proteins in gel electrophoresis, and isotope dilution quantification of biomolecules. The paper can be considered as a followup of a previous review by the author on a similar topic (: J. Szpunar, Analyst, 2000, 125, 963).

Advances in analytical methodology for bioinorganic speciation analysis: metallomics, metalloproteomics and heteroatom-tagged proteomics and metabolomics

Isotope dilution analysis for elemental speciation: a tutorial review

The emerging field of metallomics refers to the entirety of research activities aimed at the understanding of the molecular mechanisms of metal-dependent life processes. This critical review discusses the concept of metallomics with a focus on analytical techniques and methods for the probing of interactions between metal ions and the organism’s genome and the derived -omes: proteome and metabolome. Particular attention is paid to the in vivo screening for the native metal–protein and metal–metabolite complexes by hyphenated techniques that combine a high-resolution separation technique (gel electrophoresis, chromatography or capillary electrophoresis) with sensitive elemental (inductively coupled plasma, ICP) or molecular (electrospray or MALDI) mass spectrometric detection. The contribution of bioinformatics to the prediction of metal-binding sequences in proteins and the role of molecular biology approaches for the detection of metal-dependent genes, proteins and metabolites are highlighted (115 references).

Metallomics: the concept and methodology

A post-column isotope dilution analysis (IDA) methodology has been applied to carry out the quantitative speciation of selenium in human serum by affinity chromatography coupled to inductively coupled plasma mass spectrometry (ICP-MS) with an octapole reaction system (ORS). The interfering argon dimers on the 78Se and 80Se isotopes were suppressed by pressurizing the octapole chamber with hydrogen. The separation of the selenium-containing proteins was evaluated both by anion exchange chromatography (Mono Q HR 5/5) and affinity chromatography (Hi-Trap Heparin- and Hi-Trap Blue-Sepharose columns). Quantification of selenium was performed by post-column isotope dilution analysis by continuous mixing of an enriched 77Se spike solution with the eluent from the column. Finally, the 78Se/77Se or 80Se/77Se isotope ratios were monitored and the amount of selenium bound to proteins was evaluated. The chromatographic separation of selenium-containing proteins in human serum by anion exchange chromatography was not satisfactory. On the other hand, the use of affinity chromatography allowed for a rapid, precise and convenient fractionation of those proteins. Three main selenium fractions could be separated and quantified: selenoprotein P, albumin and glutathione peroxidase. Mass balance performed under different experimental conditions showed quantitative selenium recovery. The proposed methodology was used to study qualitative and quantitative speciation of selenium in human serum samples from healthy volunteers and patients on haemodialysis. The distribution of selenium between plasma glutathione peroxidase (∼20%), selenoprotein P (∼55%) and albumin (∼20%) was similar in both populations.

Quantitative speciation of selenium in human serum by affinity chromatography coupled to post-column isotope dilution analysis ICP-MS

An inductively coupled plasma quadrupole mass spectrometer (ICP-QMS) with an octapole reaction system (ORS) was used for the determination of selenium by isotope dilution analysis (IDA) in biological reference materials and serum samples from healthy subjects. The potentially interfering argon dimers (40Ar38Ar+ and 40Ar2+) at the selenium masses 78 and 80 were almost eliminated by the use of hydrogen as reaction gas. Thus, the detection limits were improved five times for 78Se and the measurement of 80Se (the main selenium isotope with an abundance of 49.61%) is now possible. An enriched 77Se solution was prepared and characterized by reverse IDA and isotope ratios measured were 78Se/77Se and 80Se/77Se. Instrumental parameters were optimised in order to obtain optimal precision and accuracy in the isotope ratio measurement of Se by ORS-ICP-QMS. The precision achieved for the isotope ratio measurements reached 0.2%
(RSD for n
= 5) for both ratios. Systematic errors, including detector dead time (47 ± 2 ns), mass bias effects (about 3%) and spectroscopic interferences due to the presence of bromine in the samples, were corrected. The accuracy of the measured selenium isotope ratios was improved by correcting the intensity signals of the selenium isotopes for SeH+ formation (about 3%). The proposed IDA method has been applied to the determination of Se in biological reference materials (serum, urine and tissues) and the results showed good agreement with the certified values.

Determination of selenium in biological materials by isotope dilution analysis with an octapole reaction system ICP-MS

Isotope dilution analysis is proposed for the determination of selenomethionine (SeMet) in Se-enriched yeast material by high performance liquid chromatography inductively coupled plasma mass spectrometry (HPLC-ICP-MS) using a 77Se-enriched selenomethionine spike obtained by yeast growth on a 77Se-rich culture medium. Different methods of yeast enrichment with selenium were evaluated to determine the most effective one. The use of two different culture media, amount of selenium added, amount of carbon source (glucose) and harvest time were evaluated in order to characterize the total selenium incorporated by the yeast cells. The yeast proteins were hydrolysed with protease XIV, and the isotopically enriched SeMet isolated by anion exchange chromatography. The isotopic composition of the SeMet in the spike solution was determined by on-line HPLC-ICP-MS and reverse isotope dilution was used for the characterization of the spike by means of a natural SeMet standard. In the analysis of the Se-enriched yeast material, the sample was spiked with 77Se-enriched SeMet, and hydrolyzed with a non-specific enzyme (protease XIV) at 37 °C for 20 hours or using an ultrasonic probe for 1 min. Both 78Se/77Se and 80Se/77Se isotope ratios were measured by ICP-MS with collision and reaction cell after the separation of selenomethionine by HPLC. The method was applied to the determination of selenomethionine in a candidate yeast reference material (SEAS project), and the results obtained were in agreement with those reported by other laboratories.

Biosynthesis of isotopically enriched selenomethionine: application to its accurate determination in selenium-enriched yeast by isotope dilution analysis-HPLC-ICP-MS

Isotope dilution analysis (IDA) has been used to quantify total selenium, total solubilized selenium, and the selenomethionine (SeMet) amount in yeast and yeast-based nutritional supplements after ...

Application of isotope dilution analysis for the evaluation of extraction conditions in the determination of total selenium and selenomethionine in yeast-based nutritional supplements.

L. Hinojosa Reyes

Papers

Quantitative speciation of selenium in human serum by affinity chromatography coupled to post-column isotope dilution analysis ICP-MS

Determination of selenium in biological materials by isotope dilution analysis with an octapole reaction system ICP-MS

Biosynthesis of isotopically enriched selenomethionine: application to its accurate determination in selenium-enriched yeast by isotope dilution analysis-HPLC-ICP-MS

Application of isotope dilution analysis for the evaluation of extraction conditions in the determination of total selenium and selenomethionine in yeast-based nutritional supplements.

Assessment of photo-Fenton and solar photo electro-Fenton processes for the efficient degradation of asulam herbicide.