Bionanotechnology of Selenite Ions Recovery into Nanoselenium by Probiotic Strains of Lactobacteria and Tolerance of Lactobacteria to Sodium Selenite

Green synthesis of nanoparticles (NPs) using living cells is a promising and new tool in bionanotechnology. Chemical and physical methods are used to synthesize NPs, but biological methods are preferred because of their environmentally friendly, clean, safe, cost-effective, simple, and efficient sources for high productivity and purity. Aim. To investigate the processes of bioreduction of selenite ions into nanoselenium by probiotic strains of lactobacilli Lactobacillus plantarum IMV B-7679 and L. casei IMV B-7280. Methods. Cultivation of lactobacilli L. plantarum IMV B-7679 and L. casei IMV B-7280 was carried out in vials (500 cm3) on a rotary shaker (220 rpm) at 30 °C for 2 days on the Man, Rogosa, and Sharpe (MRS) broth nutrient medium. Sodium selenite was additionally added to the environment in different concentrations from 1 to 30 ppm by Se. The number of viable bacterial cells in 1 mL of suspension was determined by the method of limiting dilutions in the case of sowing aliquots on a nutrient medium containing 0.2% agar-agar. Cultures of L. plantarum IMV B-7679 or L. casei IMV B-7280 were grown in the liquid MRS broth medium with low pH in the presence or absence of Na2SeO3. The concentration of sodium selenite ranged from 1 to 30 ppm by Se level. The number of microorganisms was determined by inoculation (0.1 mL of suspension) in dense media on cups with MRS agar medium, and the seeding dose was 107 cells/Petri dish. The tolerance of lactobacilli to the selenite ions was evaluated by the decrease in the number of CFU when sowing aliquots taken from culture samples grown in the presence or absence of selenite. The results of the experiments were presented in CFU and transferred to Log CFU/cm3. The characteristics of Nano-Se were studied using transmission electron microscopy (TEM). Results. It was found that after 48 h incubation in an MRS medium with the addition of sodium selenite from 1 to 30 ppm, the culture of L. plantarum IMV В-7679 was the most resistant. Thus, enrichment of the culture medium with 30 ppm of Se in the Na2SeO3 composition led to a decrease in the number of L. plantarum IMV B-7679 to 5.17 ± 0.09 Log CFU/cm3 against 4.41 ± 0.11 Log CFU/cm3 for L. casei IMV B-7280 in the control. The use of lower concentrations (1—3 ppm of Se in Na2SeO3) did not affect the change in morphology and cultural properties of L. plantarum IMV B-7679. The ability of L. casei IMV B-7280 and L. plantarum IMV B-7679 cultures to grow on MRSA nutrient medium in the presence of 3 ppm Se was shown. Higher tolerance to sodium selenite was found for L. plantarum IMV B-7679. Thus, increasing the concentration to 30 ppm of Se in the form of Na2SeO3 led to a decrease in the viability of only the culture of L. casei IMV B-7280. That is, the studied lactobacilli showed different ability to grow in the presence of selenite ions. The formation of round electron-dense granules sizing from 30 nm to 250 nm was observed using TEM. Both probiotic strains showed the ability to restore selenite ions with the accumulation of intracellular Nano-Se and the release of Nano-Se into the culture medium, which was accompanied by color shifts from yellowish to red-brown. The partial destruction of L. casei IMV B-7280 cells under the influence of oxyanions was revealed, which was accompanied by the release of culture-synthesized electron-dense Nano-Se particles. Conclusions. The optimal conditions for the growth of L. plantarum IMV B-7679 and L. casei IMV B-7280 in the presence of Na2SeO3 were established, and it was proved that lactobacilli have different abilities to grow in the presence of selenite ions. The obtained data indicate that the investigated probiotic strains showed the ability to restore selenite ions along with the accumulation of intracellular Nano-Se and the release of Nano-Se into the culture medium.