Synthesis of Selenium Nanoparticles by Bacillus laterosporus Using Gamma Radiation

Aim: This study shows the possible synthesis of Selenium Nanoparticles (SeNPs) in aerobic optimized conditions using Bacillus laterosporus (B. laterosporus) bacterial strain.
Methodology: B. laterosporus was used to reduce selenium ions (selenite anions) to SeNPs by fermentation in Luria-Bertani Enrichment (EM) medium. Optimization of fermentation conditions using two-level full factorial design was performed. SeNPs were further characterized by UV-Vis., DLS, TEM, FT-IR, EDX and XRD analysis. SeNPs synthesis by Gamma irradiated B. laterosporus cells at different radiation doses was reported. Evaluation the probability of B. laterosporus to synthesis SeNPs by fermentation in skimmed milk aerobically. A microtiterplate assay was used to evaluate the ability of SeNPs to inhibit the biofilm formation of Pseudomonas aeruginosa. Evaluating the antimicrobial activity of some antibiotic agents upon addition of SeNPs was performed.
Results: B. laterosporus reduced the soluble, toxic, colorless selenium ions to the insoluble, non-toxic, red elemental SeNPs. Statistical analysis showed that the results were normally distributed. Temperature, incubation period and pH were significant factors in the fermentation process, in which the maximum SeNPs produced (8.37µmole/ml) was at temperature 37ºC, incubation period 48hr, pH7. The Gamma radiation exposure dose 1.5kGy gave the maximum SeNPs produced (10.01 µmole/ml). A pink color appear in the fermented milk revealing the formation of SeNPs-enriched milk. SeNPs inhibit the biofilm formation of Pseudomonas aeruginosa with a percentage reduction of 99.7%. SeNPs increase the antibacterial activity of fucidic acid by 13.6% and 28.5% against Escherichia coli and Staphylococcus aureus respectively. But with Gentamycin sulphate, no change in the antibacterial activity.
Conclusion: SeNPs can be synthesized aerobically by the probiotic B. laterosporus bacterial strain. SeNPs can be incorporated in nutraceuticals and functional foods like milk also can be used to inhibit the bacterial biofilm formation and can be added to some antibacterial creams to enhance their antimicrobial activity.