Characterization and AntimicrobialProperties of Silverand Silver Oxide Nanoparticles Synthesized by Cell-Free Extract ofa Mangrove-Associated Pseudomonas aeruginosaM6 Using Two Different Thermal Treatments.

Synthesis of silver nanoparticles by cell-free extract(CFE) of Pseudomonas aeruginosaM6isolated from a mangroveecosystem was demonstrated using two physical methods, namely, boiling(conventional thermal treatment (CTT)) and microwave treatment (MWT)at pH 9. X-ray diffraction (XRD) analysis revealed the presence ofsmaller (10.4 nm), pure silver nanoparticles synthesized via CTT (C-NPs)and larger silver oxide nanoparticles in majority with negligibleconcentration of pure silver particles by MWT. Transmission electronmicroscopy (TEM) analysis showed that C-NPs are spherical in shape.Atomic force microscopy (AFM) analysis also confirmed the presenceof large-sized, aggregated nanoparticles synthesized via MWT (M-NPs).Electrophoresis indicated the size and charge-based mobility in agarosegel (0.4%), wherein the C-NPs moved faster than M-NPs, because oftheir relatively smaller size. The zeta potential value of C-NPs andM-NPs was found to be −30.1 mV and −23.1 mV, respectively.Fourier transform infrared (FT-IR) results revealed that both C-NPsand M-NPs were capped with proteins, but with different conformations.Furthermore, TEM analysis of bacterial cells exposed to aqueous silvernitrate showed the presence of spherical silver nanoparticles accumulatedin periplasmic space, indicating the possible involvementof periplasmic nitrate reductase in this process. In addition, bothC-NPs and M-NPs have also shown good antibacterial and anticandidalactivities. Thus, marine Pseudomonas aeruginosaM6 can be a potential source for the synthesis of silver nanoparticles. [ABSTRACT FROM AUTHOR]