Extracellular Synthesis and Characterization of Silver Nanoparticles from Alkaliphilic Pseudomonas sp

Bio-nanotechnology offers eco-friendly processes for the synthesis of stable nanoparticles (NPs). We hypothesized that microorganisms isolated from the root nodules of leguminous plants would biosynthesize silver (Ag) bio-nanoparticles. Clover root nodules enriched with nutrient broth (NB) produced four distinct colonies on NA plates. Microbial colonies were purified by repeated streaking and designated as SS6, SS7, SS8, and SS9 for identification using 16S rRNA sequencing. Four species of Pseudomonas were identified with a similarity score of over 99% using the EZ Taxon search engine, and tested for extracellular biosynthesis of AgNPs. Microorganism Pseudomonas taiwanensis-SS8 with alkaliphilic growth characteristics reduced the AgNO3 solution into AgNPs in the shortest time period. AgNPs were characterized using UV-Vis spectrophotometry and electron and transmission electron microscopy. A number of physical (i.e., temperature and time) and chemical (i.e., pH and growth media) parameters were optimized. An efficient polydispersal biosynthesis of AgNPs at pH 8-9 after 48 hrs in NB growth medium was observed. In addition, the AgNPs showed antimicrobial properties against 16 commonly occurring pathogenic microorganisms.