Original Article MICROBIAL SYNTHESIS OF SILVER NANOPARTICLES USING STREPTOMYCES SP. PG12 AND THEIR CHARACTERIZATION, ANTIMICROBIAL ACTIVITY AND CYTOTOXICITY ASSESSMENT AGAINST HUMAN LUNG (A549) AND BREAST (MCF-7) CANCER CELL LINES PALLAVI S. S. a , MEGHASHYAMA PRABHAKARA BHAT a , SREENIVASA NAYAKA a* a P. G. Department of Studies in Botany, Karnatak University, Dharwad 580003, Karnataka, India Email: sreenivasankud@gmail.com Received: 23 Apr 2021, Revised and Accepted: 22 Jun 2021 ABSTRACT Objective: Synthesis of silver nanoparticles using Streptomyces sp. PG12 and their characterization, antimicrobial activity and cytotoxicity against A549 and MCF-7 cancer cell lines. Methods: The silver nanoparticles were subjected to UV-Vis. spectroscopy, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM/EDS), high-resolution transmission electron microscopy (HR-TEM), zeta potential, and X-ray diffractometry (XRD) analyses. Further, the antimicrobial potential was determined by using the agar well diffusion method and cytotoxicity was determined with the help of cell viability (MTT) assay and reactive oxygen species (ROS) assay. Results: The initial indication of silver nanoparticles synthesis was noticed by the colour change in the reaction mixture and the absorption maximum at 421 nm in UV-Vis. analysis; whereas, the FTIR analysis displayed the biological functional groups responsible for the capping and stabilization of silver nanoparticles. SEM and TEM micrographs revealed the surface morphology, spherical shape, and smallest particle size as 18.91 nm. The EDS and XRD patterns confirmed the involvement of various elements during the synthesis of silver nanoparticles and the crystalline, face-centered cubic nature, respectively. The silver nanoparticles displayed considerable antimicrobial activity against human pathogens even at low MIC and MBC concentrations and exhibited increased anticancer activity against A549 and MCF-7 cell lines, where the ability of silver nanoparticles to significantly restrict the growth of tumour cells was observed at IC50 values of 69.04µg/ml and 138.30µg/ml, respectively. Conclusion: Streptomyces sp. PG12 synthesized silver nanoparticles show significant anticancer activity against A549 and MCF-7 cell lines. Keywords: Silver nanoparticles, Streptomyces sp., Antimicrobial activity, ROS expression, Human lung and breast cancer cell lines © 2021 The Authors. Published by Innovare Academic Sciences Pvt Ltd. This is an open access article under the CC BY license (https://creativecommons.org/licenses/by/4.0/) DOI: https://dx.doi.org/10.22159/ijpps.2021v13i8.41876. Journal homepage: https://innovareacademics.in/journals/index.php/ijpps. INTRODUCTION Nanotechnology is the concept that deals with the production, manipulation, characterization, and applications of nano-scale materials whose size usually ranges between 1 to 100 nm. Nano- materials prepared from metals offer unique properties of size, shape, and larger surface area to volume ratio [1]. In the recent decade, these metal nanoparticles prepared using gold, silver, platinum, copper, zinc, lead, iron, and many more are extensively used for various applications in divergent fields such as nano- medicine, electrical, agriculture, pharmaceuticals, cosmetics, food industry, textiles, and data storage [2, 3]. Silver is more often considered for synthesizing nanoparticles due to potential antimicrobial, antioxidant, anti-inflammatory, and anticancer activities. The recent advancements in nano-science have pointed out the significance of silver nanoparticles (AgNPs) in the areas of biomedical, DNA sequencing, biological sensors, plasmonics, catalysis, energy generation, and clean water technology [4, 5]. Generally, AgNPs are produced by one of two paths, i.e., ‘top-down’ or ‘bottom-up’ strategies via physical or chemical or biological synthesis routes. The physical and chemical techniques require more energy, thermal ablation, and hazardous chemicals that are carcinogenic and induce genotoxicity. Hence, due to its low cost, non-toxicity, and eco-friendly nature, the biological synthesis method is essential [6, 7]. The greener approach of AgNPs synthesis is carried out by employing biological resources like algae, lichens, bacteria, yeast, fungi, actinobacteria, and plant extracts. Among the microorganisms, bacteria are considered the ideal source for metal nanoparticles synthesis, owing to their metal resistance mechanism, which helps them reduce ionic silver (Ag + ) into elemental (Ag°) NPs [8, 9]. The microbial synthesis method of AgNPs allows for safer, cheaper, and more stable metallic AgNPs as the microbes produce various secondary metabolites, which actively participate in the reduction, capping, and stabilization [10]. The increasing multi-drug resistance in human pathogenic microorganisms is of great concern, and there is an urgent need for the development of broad-spectrum antimicrobials to treat severe infections. The AgNPs have gained importance as the alternative for antibacterial and antifungal agents and help reduce toxicity, avoid the side effects in patients, and prevent pathogens [11, 12]. Cancer is ranked top on the list of deadly diseases as the second leading cause for the most deaths across the globe, and the numbers are expected to increase further [13]. From the past few decades, AgNPs are extensively used as cytotoxic agents against various human cancers. The microbial AgNPs synthesized using species of Pseudomonas [14], Enterococcus [15], and Streptomyces [16, 17] have successfully prevented the growth of tumour cells. Actinomycetes belong to Gram-positive, aerobic and filamentous bacteria with high G+C content. Many of the Actinomycetales members are known for their peculiar capacity to produce bioactive secondary metabolites having properties from antimicrobial to anticancer and many more [18-20]. Because of these essential biological properties of actinobacterial secondary metabolites, the culture filtrate of Streptomyces sp. PG12 was to investigate for the extracellular synthesis of AgNPs and their evaluation for antimicrobial and anticancer potential. MATERIALS AND METHODS Collection of pathogens The pathogenic microorganisms such as Staphylococcus aureus (MTCC6908), Pseudomonas aeruginosa (MTCC424), Enterococcus International Journal of Pharmacy and Pharmaceutical Sciences Print ISSN: 2656-0097 | Online ISSN: 0975-1491 Vol 13, Issue 8, 2021