Conversion of inorganic selenium to organic form(s) by Lactobacillus acidophilus

Abstract

The bioconversion of 2 forms of inorganic selenium namely selenite (SeIV) and selenate (SeVI) to organic form(s) by Lactobacillus acidophilus strain was investigated. The cultured media (MRS) was supplemented with 1, 2, 5, 10, 20 ppm of Se in the form of sodium selenite (Na 2 SeO 3 , SeIV) or sodium selenate (Na 2 SeO 4 , SeVI) and incu-bated at 37°C up to 24 hr Both Se forms showed no marked effect on the bacterial growth indicating no cytotoxicity at these concentrations. However, the media supplemented with 5, 10 and 20 ppm of Se(IV), but not Se(VI), became reddish after 24 hr of incubation with increasing the red color intense with increasing the Se content in the media. The scanning electron microscope (SEM) investigation clarified the presence of Se-nano particles (SeNPs) in the media. Se speciation of the cultured media supernatant and its corresponding cell fractions using HPLC-ICP-MS technique indicated that the bioconversion rate of Se to organic form(s) was extremely higher in Se(IV) than Se(VI) in both fractions however, the cell fractions contained the highest content. The organic Se gradually increased in both fractions with increasing the media Se content. The inorganic Se was completely bio-converted to organic form(s) without any residual only in the medium contained 1 ppm Se(IV). Our results demonstrate the ability of L. acidophilus to convert Se(IV) but not Se(VI), at a limit concentration of 1 ppm and accumulate organic Se form(s) in the cell fraction. These results confirm the possible bio-production of organic Se enriched fermented dairy products.