Biogenic Synthesis of Gold Nanoparticles by Plant-Growth-Promoting Bacteria Isolated from Philippine Soils
Plant-growth-promoting bacteria (PGPB) and actinomycetes isolated from Philippine soils were screened for their ability to extracellularly synthesize gold nanoparticles (Au0) from ionic gold (Au3+). Sixteen isolates, which include 12 PGPBs and four actinomycetes, were tested for the presence of nitrate reductase activity. Nitrate reductase is one of the enzymes responsible in the bioreduction of ionic gold. Ten PGPBs exhibited nitrate reductase activity after 5 d of incubation at 37 °C. All the four tested actinomycetes did not exhibit the aforementioned enzyme activity. Promising PGPB isolates for gold nanoparticle synthesis were selected based on their level of nitrate reductase activity. Extracellular synthesis of gold nanoparticles was determined by incubation of the PGPB culture supernatant with gold (III) chloride trihydrate (HAuCl4•3H2O) for 7 d at 28 °C. UV/Vis scanning spectroscopy of the culture supernatants of PGPBs 1 and 5 showed absorbance peaks of gold nanoparticles at 570 nm and 541 nm, respectively. Transmission electron microscopy (TEM) of the promising PGPBs 1 and 5 showed the presence of gold nanoparticles in the 10–100 nm size range. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) analysis confirmed the production of gold nanoparticles by PGPB 5.
Key Words: electron microscopy, gold nanoparticles, green chemistry, nanotechnology, plant-growth-promoting bacteria
Abbreviations: AuNPs – gold nanoparticles, EDX – energy dispersive X-ray, NADH – reduced form of nicotinamide adenine dinucleotide, NB – nutrient broth, NEED – N-(1-napthy) ethelenediamine dihydrochloride solution, PGPB – plant-growth promoting bacteria, SEM – scanning electron microscopy, TEM – transmission electron microscope