Selenium accumulation and biotransformation in Streptococcus, Lactococcus, and Enterococcus strains

Abstract

• Strains from LAB can accumulate and biotransform sodium selenite from growth medium. • First description of Se produced by Lactococcus lactis subsp. cremoris. • LAB transforms Se into selenocysteine and nanoparticles. • Se-enriched LAB can be used to develop new functional foods for humans. In the present study, we evaluated the ability of inorganic Se to accumulate and biotransform into different selenium species and Se nanoparticles (SeNPs) in seven bacteria from the Lactococcus , Streptococcus, and Enterococcus genera . The cytotoxicity of selenized strains to human adenocarcinoma Caco-2 and HT29 cells, the effect of selenium enrichment on antioxidant activity, and cell surface hydrophobicity of the tested strains were determined. When compared to that of lactococci and enterococci, increasing concentrations of sodium selenite in the cultivation media inhibited the growth of Streptococcus thermophilus strains. Thirty milligrams per liter Na 2 SeO 3 and its higher concentrations (50 and 100 mg/L) significantly reduced the viability of Caco-2 and HT29 cells by 40–75%. Bacteria mainly produced SeNPs and selenocysteine in Se form. Our results indicate that the tested strains can accumulate and transform inorganic selenium, which makes them promising candidates for selenization and possible application in functional foods.