Selenocysteine Formation by <i>Enterococcus faecium</i> ABMC-05 Follows a Mechanism That Is Not Dependent on Genes <i>sel</i>A and <i>sel</i>D but on Gene <i>cys</i>K

Abstract

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.

Keywords

• selenocysteine
• selenium
• lactic acid bacteria
• selenoproteins