Abstract
An analytical approach was developed to study the incorporation of selenium (Se), an important trace element involved in the protection of cells from oxidative stress, into the well-known probiotic Lactobacillus reuteri Lb2 BM-DSM 16143. The analyses revealed that about half of the internalized Se was covalently incorporated into soluble proteins. Se-enriched proteins were detected in 2D gels by laser ablation inductively coupled plasma mass spectrometry imaging (LA-ICP MSI) and identified by capillary HPLC with the parallel ICP MS ((78)Se) and electrospray Orbitrap MS/MS detection. On the basis of the identification of 10 richest in selenium proteins, it was demonstrated that selenium was incorporated by the strain exclusively as selenocysteine. Also, the exact location of selenocysteine within the primary sequence was determined. This finding is in a striking contrast to another common nutraceutical, Se-enriched yeast, which incorporates Se principally as selenomethionine.
Highlights
In recent years selenium (Se)1 has received considerable attention as an essential element for human health
Selenium Uptake by L. reuteri Lb2 BM-DSM 16143 During Growth—The ICP-MS analyses were performed on the pellet, supernatant and EDTA wash recovered from cultures of L. reuteri grown as described in the Experimental section
Experiments on selenium uptake by L. reuteri Lb2 BM-DSM 16143 during growth demonstrated the ability of the strain to recover selenium from the medium
Summary
In recent years selenium (Se) has received considerable attention as an essential element for human health. Se occurs in nature principally in four inorganic chemical forms: the highly toxic selenide (Se2ϪϪ) (4), the moderately toxic selenate (SeO42ϪϪ) and selenite (SeO32ϪϪ), and elemental selenium (Se0) which is essentially nontoxic and can be stored by several bacterial species as. Inorganic selenium can be converted by biological systems (microorganisms, plants, and mammals) into seleno-amino acids, which are incorporated into proteins. The two most common seleno-amino acids are selenomethionine (SeMet) and selenocysteine (SeCys). The former is synthesized via a route similar to the sulfur metabolic pathway in which selenium substitutes sulfur with no alteration of the protein structure (8, 9). Selenoproteins containing genetically encoded SeCys are known to be synthesized by several bacteria. Because L. reuteri species are native inhabitants of human microbiota, the association of the probiotic feature L. reuteri Lb2 BM-DSM 16143 with its ability to fix selenium into proteins, offers an innovative approach to combat human selenium deficiency
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