Biogenic Synthesis and Nematicidal Potential of Silver Nanoparticles Derived from Indigenous Microbes of Vietnam's Central Highlands.

Green silver nanoparticles (AgNPs) biosynthesis via microbe-mediated processes has many advantages, attracting much attention in research. In this study, the biosynthesis of green AgNPs using cell-free fermented broth (CFFB) of native bacterial strains in the Vietnam Central Highlands jungle was first exploited. After screening more than 60 strains, CFFB from strain LV-V3 showed the most effective AgNPs biosynthesis ability, with AgNPs synthesis efficiency of 76.7809%. This potential strain was identified as Pantoea coffeiphila via 16S rRNA gene sequence identification. The most suitable condition for green AgNPs biosynthesis was determined at a AgNO₃/CFFB ratio of 3:1, a CFFB dilution of 1:20, 1.5 mM AgNO₃, 70 °C, pH 6, and a 48-h reaction time. AgNPs characteristics were evaluated via UV-Vis, SEM, TEM, XRD, and FTIR analysis. The obtained AgNPs are spherical and small in average size (8.5 nm). Furthermore, their stability was examined over 3 months, showing high stability with their shape, UV-Vis absorption, and zeta potential, with no significant change. The novel bioactivity of these green AgNPs was evaluated against the black pepper nematode. The inhibition of both egg-hatching and second-stage juveniles of AgNPs was much better than that of CFFB at all tested concentrations. Evidence of the penetration ability of AgNPs biosynthesized from P. coffeiphila LV-V3 fermented broth into eggs and juveniles, involved in its strong anti-nematode effect, was also elucidated. This research indicated green AgNPs from a novel microbial source from the Vietnam Central Highlands jungle for effectively managing plant-parasitic nematodes.