Biotransformation of Selenium by Lactic Acid Bacteria: Formation of Seleno-Nanoparticles and Seleno-Amino Acids

Abstract

Selenium (Se) is an essential micronutrient for the majority of living organisms, and it has been identified as selenocysteine in the active site of several selenoproteins such as glutathione peroxidase, thioredoxin reductase, and deiodinases. Se deficiency in humans is associated with viral infections, thyroid dysfunction, different types of cancer, and aging. In several European countries as well as in Argentina, Se intake is below the recommended dietary Intake (RDI). Some lactic acid bacteria (LAB) can accumulate and bio-transform selenite (toxic) into Se-nanoparticles (SeNPs) and Se-amino acids (non-toxic). The microbial growth, Se metabolite distribution, and the glutathione reductase (involved in selenite reduction) activity of Se-enriched LAB were studied in this work. The ninety-six assayed strains, belonging to the genera Lactococcus, Weissella, Leuconostoc, Lactobacillus, Enterococcus, and Fructobacillus could grow in the presence of 5 ppm sodium selenite. From the total, eight strains could remove more than 80% of the added Se from the culture medium. These bacteria accumulated intracellularly between 1.2 and 2.5 ppm of the added Se, from which F. tropaeoli CRL 2034 contained the highest intracellular amount. These strains produced only the selenoamino acid SeCys as observed by LC-ICP-MS and confirmed by LC-ESI-MS/MS. The intracellular SeCys concentrations were between 0.015 and 0.880 ppm; Lb. brevis CRL 2051 (0.873 ppm), Lb. plantarum CRL 2030 (0.867 ppm), and F. tropaeoli CRL 2034 (0.625 ppm) were the strains that showed the highest concentrations. Glutathione reductase activity values were higher when the strains were grown in the presence of Se except for the F. tropaeoli CRL 2034 strain, which showed an opposite behavior. The cellular morphology of the strains was not affected by the presence of Se in the culture medium; interestingly, all the strains were able to form spherical SeNPs as determined by transmission electron microscopy (TEM). Only two Enterococcus strains produced the volatile Se compounds dimethyl-diselenide identified by GC-MS. Our results show that Lb. brevis CRL 2051, Lb. plantarum CRL 2030, and F. tropaeoli CRL 2034 could be used for the development of nutraceuticals or as starter cultures for the bio-enrichment of fermented fruit beverages with SeCys and SeNPs.

Selenium in Human Health and Gut Microflora: Bioavailability of Selenocompounds and Relationship With Diseases

“…The metabolic pathways of selenium biotransformation in gut microbiota remain unclear, even though some bioproducts from Se metabolizing organisms enriched with sodium selenite have been manufactured (137). The rationale behind the use of selenium and probiotic co-supplementation is based on the antioxidant and anti-inflammatory effects of this treatment as observed in the metabolic responses of animal models.…”

“…In case of normal levels of Se, the thyoredoxin reductase system and SH-Px protect the thyrocytes from the activity of peroxides, whereas the apoptotic response to H 2 O 2 is increased with Se deficiency (136). For instance, the decrease in the levels of Lactobacillus can interfere with the formation of iodothyronine deiodinases (DIOs) and, consequently, might result in thyroid dysfunctions (109,137).…”

Effects of Selenium- and Zinc-Enriched Lactobacillus plantarum SeZi on Antioxidant Capacities and Gut Microbiome in an ICR Mouse Model

“…It might be caused by utilization of selenium and zinc by Lactococcus spp. According to the previous studies, Lactococcus lactis is capable of selenium biotransformation and zinc uptake [ 57 , 58 ]. The relative abundance of Allobaculum spp., which was markedly reduced in the SZ + Lp group compared with other groups, was reported to be adversely associated with mRNA expression levels of tight junction protein genes ( zo-1 and occludin ) and anti-inflammatory genes ( foxp3 and Il-10 ) in the colon of rats [ 59 ].…”

Bioaccumulation of selenium-by fruit origin lactic acid bacteria in tropical fermented fruit juices

“…Although Se has been added in the soil for fortifying crops, its absorption and biotransformation into organic and more available forms depends on the plant species. Some LAB can biotransform inorganic sodium selenite into organic Se nanoparticles and seleno-amino acids (SeMet and SeCys) (Martínez, Martin-Moreno, Pescuma, Madrid-Albarrán, & Mozzi, 2020). At the moment, consumers demand for functional foods with low caloric content, high nutritional value, and free of milk derivatives are continuously increasing (Granato, Branco, Cruz, Faria, & Nazzaro, 2010).…”