Biotransformation of selenium by Lactobacillus reuteriCRL1101 and L. acidophilus CRL 636

MICAELA PESCUMA; BEATRIZ GOMEZ GOMEZ; GRACIELA FONT DE VALDEZ; TERESA, PEREZ-CORONA; YOLANDA, MADRID; FERNANDA MOZZI

Simposio; V simposio internacional de bacterias lacticas; 2016

CERELA

Selenium (Se), anessential trace element, is present as SeCys (Sec, amino acid) in proteins(selenoproteins) involved in antioxidant functions, thyroid hormone production,viral expression genes, etc. Se should be consumed as elemental or organic formto be non-toxic. Animals incorporate Se via plants that absorb Se from the soiland transform inorganic Se into organicforms such as methylated low-molecular-weight selenium compounds (selenomethionine,SeMet) which is a precursor for Sec. In addition, some lactic acidbacteria are able to bio-transform Se into elemental Se nanoparticles, SeCys2,SeMeSeCys and SeMet; these compounds being known to have antioxidant propertiesand to arrest the cell cycle of cancer cells. The aim of thiswork was to evaluate the ability of Lactobacillusreuteri CRL 1101 and Lactobacillusacidophilus CRL 636, species commonly used in fermented foods, to transformand accumulate Se. The strains were grown in MRS supplemented with 5 mg/L ofSeO3Na2 at 37°C during 24 h. Cell viability was monitoredby cell count (cfu/mL) and OD600. The release of elemental Se as nanoparticleswas analyzed by TEM (JOEL JEM 2100) equipped with an X-ray energydispersive (XEDS) microanalysis composition system. Se accumulation wasanalyzed by ICP-MS (Agilent 7700) after total microwave digestion, and Sespecies by using an LC-ICP-MS with a reverse phase C8 and an ionexchange column (PRP-X100) after enzymatic digestion. Results showed that viabilityof L. reuteri CRL 1101 after 24 hincubation in the presence of Se was 1 U log lower than in the control, while agreater deleterious effect (3 U log) of Se was observed in L. acidophilus CRL 636.  TEManalysis showed the presence of spherical Se nanoparticles with sizes between25 and 130 nm in both cell cultures. Interestingly, in L. reuteri CRL 1101 cultures nanoparticles were embedded in acarbon matrix of likely exopolysaccharides; this feature was not observed in L. acidophilus CRL 636 for which celllyses was detected. L. reuteriaccumulated 78% of the added Se in the cell while L. acidophilus CRL 636 41% after 24 h incubation. LC-ICP-MSanalysis showed that both stains were able to accumulate Se intracellularly asSeCys2 and SeMet while the presence of SeMeSeCys was observed only inL. reuteri CRL 1101. These strainscould be used to formulate Se-enriched foods for delivering these antioxidant compoundsto individuals with Se deficiencies.