Proteomic characterization of a selenium‐metabolizing probiotic Lactobacillus reuteri Lb2 BM for nutraceutical applications

Abstract

Selenium (Se), Se-cysteines and selenoproteins have received growing interest in the nutritional field as redox-balance modulating agents. The aim of this study was to establish the Se-concentrating and Se-metabolizing capabilities of the probiotic Lactobacillus reuteri Lb2 BM, for nutraceutical applications. A comparative proteomic approach was employed to study the bacteria grown in a control condition (MRS modified medium) and in a stimulated condition (4.38 mg/L of sodium selenite). The total protein extract was separated into two pI ranges: 4-7 and 6-11; the 25 identified proteins were divided into five functional classes: (i) Se metabolism; (ii) energy metabolism; (iii) stress/adhesion; (iv) cell shape and transport; (v) proteins involved in other functions. All the experimental results indicate that L. reuteri Lb2 BM is able to metabolize Se(IV), incorporating it into selenoproteins, through the action of a selenocysteine lyase, thus enhancing organic Se bioavailability. This involves endo-ergonic reactions balanced by an increase of substrate-level phosphorylation, chiefly through lactic fermentation. Nevertheless, when L. reuteri was grown on Se a certain degree of stress was observed, and this has to be taken into account for future applicative purposes. The proteomic approach has proven to be a powerful tool for the metabolic characterization of potential Se-concentrating probiotics.

Selenium effects on the metabolism of a Se-metabolizingLactobacillus reuteri: analysis of envelope-enriched and extracellular proteomes

“…5). Phosphoketolase has been observed to be induced in both in toto proteome 27 and cell-envelope enriched proteome, and identified in this experiment analyzing extracellular proteome. It probably belongs to the so-called moonlighting proteins that display the ability to be present in different cellular districts.…”

“…Furthermore this result is in agreement with the observed stimulation of the energygenerating routes (glycolysis and pentose-phosphate pathway) resulting in enhanced ATP synthesis. 27 Elongation factor Tu (spot 8) is up-regulated under the stimulated conditions. This protein, normally present in the cytosol and involved in protein synthesis, is described as a moonlighting protein, since it is responsible for adhesion when surface-exposed.…”

“…It has been previously demonstrated that the growth on selenium can cause a certain degree of stress in L. reuteri: GroEL and GrpE, two well known stress protein, were up-regulated in the presence of 4.38 mg L À1 sodium selenite. 27 ClpP is a serine protease that degrades small peptides (o7 amino acids). In Lactococcus lactis ClpP is involved in the degradation of misfolded proteins originated after stress exposure.…”

“…In a previous paper 27 the up-regulation of a selenocysteine lyase, involved in the selenium-fixing process, has been demonstrated by in toto proteome analyses in a probiotic LAB: Lactobacillus reuteri Lb2 BM DSM 16143 grown in a sodium selenite medium.…”

“…27 More recent results revealed that the same strain has the capability to specifically fix inorganic selenium into the selenocysteines of 7 enzymes involved in different pathways within the cell: glyceraldehyde 3-phosphate dehydrogenase, pyruvate kinase, phosphoketolase, 6-phosphogluconate dehydrogenase, arginine deiminase, ornithine carbamoyltransferase and ribonucleoside hydrolase RihC. 28 The aim of the present study was to investigate L. reuteri Lb2 BM DSM 16143 sub-proteomes, such as the envelope-enriched fraction and extracellular compartment, in order to complete an overall study dealing with the influence of selenium on the metabolism of this probiotic confirming its potential as a nutraceutical supplement.…”