No abstract

Selenium nanoparticles (SeNPs) are gaining importance in the food and medical fields due to their antibacterial properties. The microbial inhibition of these kinds of particles has been tested in a wide range of Gram (+) and Gram (−) pathogenic bacteria. When SeNPs are synthesized by biological methods, they are called biogenic SeNPs, which have a negative charge caused by their interaction between surface and capping layer (bioorganic material), producing their high stability. This review is focused on SeNPs synthesis by bacteria and summarizes the main factors that influence their main characteristics: shape, size and surface charge, considering the bacteria growth conditions for their synthesis. The different mechanisms of antimicrobial activity are revised, and this review describes several biosynthesis hypotheses that have been proposed due to the fact that the biological mechanism of SeNP synthesis is not fully known.

No abstract

Lactic acid bacteria have been studied for their ability to accumulate inorganic selenium, which is reduced to its elemental form or could be integrated into selenoproteins in the form of selenocysteine. This ability to produce bioavailable organic selenium for humans is an advantage that could be exploited in the production of functional foods. In this work, Enterococcus faecium ABMC-05 isolated from a traditional Mexican beverage (tepache) and with NCBI entry number OL413240 was used. Microorganism selenization was performed after the determination of minimal inhibitory concentration of Na 2 SeO 3 (184 mg/L), which was calculated using the graphical method of Talmadge and Fitch. The selenium concentration of accumulated selenium was calculated by inductively coupled plasma optical emission spectroscopy (ICP-OES). The concentration of selenium at 48 h of fermentation was 39.92 mg/L, which represented 23.8% of selenium at medium. This value was consistent with those reported for other lactic acid bacteria. Finally, it was determined the selenocysteine presence in biomass recovery after fermentation using RP-HPLC technique. With these results it was confirmed the biogenic production of selenocysteine by Enterococcus faecium ABMC-05 using an inorganic source.

Lactic acid bacteria (LAB) resist sodium selenite of concentrations greater than 100 mg/L in fermentation media. Selenium affects the growth rate, but once the microorganism absorbs selenium, this element is converted through a complex mechanism into selenocysteine and then into a selenoprotein structure. This study verified the presence of selenocysteine in Enterococcus faecium ABMC-05. The microorganism was cultivated in a medium enriched with a minimum inhibitory concentration of sodium selenite (184 mg/L). The concentration of selenium absorbed and the bioconversion into selenocysteine were determined by inductively coupled plasma optical emission spectrometry (ICP-OES) and reverse-phase high-performance chromatography (RP-HPLC), respectively. The presence of the selD, selA, and cysK genes was determined by amplifying the 16S rDNA through polymerase chain reaction (PCR). The microorganism accumulated inorganic selenium, and part was transformed into selenocysteine. The growth curves were atypical for a lactic acid bacterium with a stationary phase greater than 70 h. Determining the genetic expression showed only the presence of the cysK gene and the absence of the selD and the selA genes. The results demonstrate that this microorganism produces selenocysteine through a mechanism independent of the SelA and SelD pathways in contrast to other LAB.