Biogenic production of selenocysteine by Enterococcus faecium ABMC-05: an indigenous lactic acid bacterium from fermented Mexican beverage

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.

Selenocysteine Formation by Enterococcus faecium ABMC-05 Follows a Mechanism That Is Not Dependent on Genes selA and selD but on Gene cysK

“…The bacterium was reported previously by our research group [21], but the identification methodology has yet to be reported. Thus, the microorganism was identified by combining MALDI mass spectrometry (matrix-assisted laser desorption/ionization), TOF (time of flight), and MALDI BioTyper software.…”

“…The experiment was carried out in separate tubes. With the viability data obtained, the MIC was determined according to the graphic method of Talmadge and Fitch reported by Escobar-Ramírez et al [21].…”

“…Escobar-Ramírez et al [20] reported the isolation of five different LAB from tepache, one of which showed probiotic characteristics. However, few studies have demonstrated the selenization of LAB isolated from traditional Mexican fermented beverages [21].…”

“…In general, LAB has shown a low tolerance to selenite stress and a low ability to reduce high concentrations of selenite [9,15,21,36,37]. However, Estrada et al [13] showed that Enterococcus sp.…”

“…They determined that at 80 mg/L of Na 2 SeO 3 , the cell concentration of different LAB growing in a similar medium decreased. However, this concentration was the same as that calculated using the OD method to measure the microbial growth of E. faecium ABMC-05 in previous work [21]. In addition, in this case, the first inflection in the curve of the inhibitory experiment was calculated at 36 and 48 h because the microorganism concentration decreased from 8 to 5 log CFU/mL at the two first concentrations of Na 2 SeO 3 assayed (100 and 200 mg/L, respectively) (Table 1).…”