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Stable isotope labeling in cell culture (SILAC) was applied for the first time on a lactic acid bacterium strain (L. reuteri CRL1101) for analyzing differential protein expression associated to selenite(Na2SeO3) and selenium nanoparticles (SeNPs) exposure. 57 and 47 proteins were found de-regulated by >1,5 fold in presence of selenite and SeNPs, respectively. Only 16 out of 104 proteins differentially expressed were commonly altered by selenite and SeNPs. The use of a clustered heat map allows us to visualize relations between the de-regulated proteins and exposure conditions. We identified a number of proteins involved in diverse functions and biological processes such as metabolism of carbohydrates, selenium and lipids; folding, sorting and degradation; environmental information and processing. In presence of both, selenite and SeNPs, proteins related to selenium metabolism such as cystathione beta-lyase and oxidoreductases (thioredoxine reductase and NAD/FAD oxidoreductase) were over expressed. Interestingly, the over expression of thioredoxin reductase could protect the host from oxidizing compounds. An over expression of phage proteins and chaperones with selenite was observed; this result and the fact that a lower cell count was detected when selenite was added could indicate that this latter Se species has a more deleterious effect than the nanoparticles., Ministry of Economy and Competitiveness, Community of Madrid, FEDER program, Depto. de Química Analítica, Fac. de Ciencias Químicas, TRUE, pub

Selenium nanoparticles (SeNPs) were synthesized by a green technology using lactic acid bacteria (LAB, Lactobacillus acidophilus, L. delbrueckii subsp. bulgaricus and L. reuteri). The exposure of aqueous sodium selenite to LAB led to the synthesis of SeNPs. Characterization of SeNPs by transmission electron microscopy with energy dispersive X-ray spectrum (EDXS) analysis revealed the presence of stable, predominantly monodispersed and spherical SeNPs of an average size of 146 ± 71 nm. Additionally, SeNPs hydrodynamic size was determined by dispersive light scattering (DLS) and nanoparticle tracking analysis (NTA). For this purpose, a methodology based on the use of surfactants in basic medium was developed for isolating SeNPs from the bacterial pellet. The hydrodynamic size values provided by DLS and NTA were 258 ± 4 and 187 ± 56 nm, respectively. NTA measurements of number-based concentration reported values of (4.67±0:30)x 109 SeNPs/mL with a relative standard deviation lower than 5% (n = 3). The quantitative results obtained by NTA were supported by theoretical calculations. Asymmetrical flow field flow fractionation (AF4) on line coupled to the inductively couple plasma mass spectrometry (ICP-MS) and off-line coupled to DLS was further employed to characterize biogenic SeNPs. The distribution of the particle size for the Se-containing peak provide an average size of (247 ± 14) nm. The data obtained by independent techniques were in good agreement and the developed methodology, Spanish Commission of Science and Technology, Community of Madrid, FEDER, Depto. de Química Analítica, Fac. de Ciencias Químicas, TRUE, pub

Selenium, which is present as SeCys in selenoproteins, is involved in cancer prevention, thyroid functioning, and pathogen inhibition. Lactobacilli can biotransform inorganic Se into seleno-amino acids. Growth, Se accumulation and seleno-amino acid formation by Lactobacillus acidophilus CRL636 and L. reuteri CRL1101 in a Se-supplemented medium were studied. Moreover, survival of Se-enriched strains to different pH values and bile salts was analyzed. L. acidophilus CRL636 showed low growth rate in the presence of Se while differences were less evident for L. reuteri CRL1101, which displayed higher amounts of intracellular SeCys and SeMet than the CRL636 strain. Interestingly, both lactobacilli could produce Se-nanoparticles. Se-enriched lactobacilli showed lower growth rates than non-Se exposed cells. The adverse effect of bile salts and the ability to survive at pH 4.0 diminished for the Se-enriched L. reuteri strain. The studied lactobacilli could be used as Se-enriched probiotics or as a vehicle for manufacturing Se-containing fermented foods., CONICET, Argentina, Spanish Commission of Science and Technology, Community of Madrid, Depto. de Química Analítica, Fac. de Ciencias Químicas, TRUE, pub