Biosynthesis and characterization of zinc oxide nanoparticles from an estuarine-associated actinobacterium Streptomyces spp. and its biotherapeutic applications.

The present study was conducted to biosynthesize zinc oxide nanoparticles (ZnONPs) by an estuarine associated actinobacterium Streptomyces spp., characterized its spectral features and also determined its biomedical properties. At first, ZnONPs were synthesized by actinobacterial-mediated reduction of zinc oxide metal and then, it was characterized by following standard methodologies. The biosynthesized ZnONPs were confirmed through the reduction of Zn ions with the strong intensity range (3 eV) at zinc region and the absorption range of 363 nm. The XRD pattern of biosynthesized ZnONPs showed six intensive peaks with 2θ values of 36.38-83.34º. This ZnONPs exhibited spherical in shape with the average size ranges in between 51.42 and 65.13 nm. The antimicrobial efficacy of various concentrations of ZnONPs was determined against both bacterial and fungal pathogens and it revealed the highest growth inhibition against E. coli (22 mm) at 20 μl concentration with the respective MIC and MBC values of 0.625 μg/ml and ≤ 2.5 μg/ml. Similarly, the antifungal activity represented the maximum (20 mm) zone of growth inhibition against Candida fructus at 20 μl concentration. Furthermore, the in vitro antioxidant, anti-inflammatory and antibiofilm efficiency of ZnONPs were tested. The result inferred that the maximum in vitro total antioxidant activity (70.86%), DPPH (79.26%), nitric oxide (67.31%) and hydroxyl radical (76.83%) scavenging activities were noted at 125 μg/ml concentration of ZnONPs with the respective half maximal inhibitory concentration (IC50) values of 81.69, 83.42, 76.09 and 82.46 μg/ml. In in vitro anti-inflammatory activity study, the maximum concentration (500 μg/ml) of ZnONPs showed the inhibition of 94.62% with the IC50 value of 146.70 μg/ml. Finally, the ZnONPs effectively reduced the biofilm formation with the highest percentage (91.08%) of inhibition against E. coli at 75 μg/ml concentration. Based on these results, it could be concluded that the actinobacterium Streptomyces spp., mediated biosynthesized ZnONPs has biomedical potential with antimicrobial, antioxidant, antiinflammatory and antibiofilm properties.