Bacillus niabensis OAB2: Outstanding bio-factory of selenium nanoparticles

Highlights: • Bacillus niabensis OAB2 is identified as a novel selenium nanoparticles bio-producer. • Gamma irradiated cells generated selenium nanoparticles with different characters. • The biogenic selenium nanoparticles exhibited considerable antimicrobial impact. • WI38 human cell line affected by the non-irradiated selenium nanoparticles. • Adenovirus-9 showed susceptibility towards the non-irradiated selenium nanoparticles. Selenium is an essential trace element, but its oxyanions, selenite [SeO₃²⁻] or selenate [SeO₄²⁻], are ecologically toxic. Different microorganisms were reported to transform the soluble toxic selenite or selenate to the insoluble less toxic elemental selenium (Se⁰), forming selenium nanoparticles (SeNPs). In the present study, we isolated a selenate-reducing bacterial strain from Egyptian soil that showed remarkable tolerance for elevated sodium selenate concentration (40 mM). The treatment of the bacterial cells with 1 kGy gamma irradiation attained an extra ~10% SeNPs yield throughout 72 h. Furthermore, the irradiation improved the selenate reduction rate where almost half of the anions were reduced at the first 28 h of the incubation period, versus about 44 h by the control cells. The UV–Vis spectra of the SeNPs generated by the irradiated and non-irradiated cultures showed distinct variation. The XRD and Raman spectroscopy of the two generated nanoparticles proved the irradiation influence on the crystalline structures of the SeNPs. The FESEM, EDX, TEM, and DLS revealed that gamma irradiation has a serious impact on the size, shape, and composition of the generated SeNPs. Zeta potential showed that both generated SeNPs had negative charges but with different values, while FTIR inspection exhibited similar profiles for both types of SeNPs. Both the control and irradiated SeNPs exhibited diversified antimicrobial impact, which markedly peaked against Gram-positive test organisms with values greater than the antimicrobial test control. The cytotoxicity of the synthesized SeNPs versus the WI38 cell line and antiviral activities against adenovirus-9 were also inspected.