Marine Streptomyces cyaneus Strain Alex-SK121 Mediated Eco-friendly Synthesis of Silver Nanoparticles Using Gamma Radiation

Aim: The present study aimed to develop cost-effective, eco-friendly marine Streptomyces cyaneus strain Alex-SK121 mediated synthesis of silver nanoparticles (AgNPs) with antimicrobial, antitumor and antioxidant activities.
Methodology: Aqueous 1mM silver nitrate (AgNO3) solution was treated with cell-free supernatant (CFS) of a novel Streptomyces cyaneus strain Alex-SK121 isolated from marine sediment samples. The prepared solution was irradiated with different doses of gamma rays ranged from 0.5 to 30.0kGy. Initial characterization of the synthesized AgNPs was performed by visual observation of color change in the prepared solution followed by analysis of UV-Visible Spectrophotometer (UV-Vis.), Fourier Transform Infrared Spectrometer (FT-IR), Dynamic Light Scattering (DLS) and Transmission Electron Microscopy (TEM). Evaluation of antimicrobial activity of the synthesized AgNPs against some pathogenic microorganisms was carried out. Antitumor activity of AgNPs was carried out against some human cancer cell lines using the method of Sulphorodamine B (SRB) assay, antioxidant activity of AgNPs was also studied using DPPH scavenging assay.
Results: In the present study, the cell-free supernatant of Streptomyces cyaneus strain Alex-SK121 isolated from sediment samples collected from Sidi Kerir region, Alexandria governorate, Egypt was found to reduce Ag+ ions to AgNPs. Identification of the producer strain was performed according to spore morphology and cell wall chemo-type, which suggested that this strain is Streptomyces. Further cultural, physiological characteristics and analysis of the nucleotide sequence of 16S rRNA gene indicated that this strain is identical to Streptomyces cyaneus and then designated Streptomyces cyaneus strain Alex-SK121. To maximize the production of AgNPs, the tested supernatant was irradiated with different doses of gamma rays and it was found that, 15 kGy is the best applied dose induces AgNPs synthesis. The synthesized AgNPs showed the characteristic absorption spectra in UV–Vis. at 425 nm. The microbiologically synthesized AgNPs showed significant antimicrobial activity towards some pathogenic microorganisms with inhibition zone ranged from 13 up to 20 mm. Also AgNPs exhibited antitumor activity against human breast carcinoma cells and human liver carcinoma cells with IC50 9.63 and 33.75 µg/ml respectively in addition to 96% antioxidant activity.
Conclusion: Gamma irradiation which induced AgNPs synthesis by cell-free supernatant of marine actinomycetes Streptomyces cyaneus strain Alex-SK121 with different applications is a simple, clean, economic and environmental friendly approach.