Biosynthesis of silver nanoparticles using actinomycetes, phytotoxicity on rice seeds, and potential application in the biocontrol of phytopathogens

Abstract

To find effective silver nanoparticles (AgNPs) for control of phytopathogens, inthis study, two strains of actinomycetes isolated from the soil of the Brazilianbiome Caatinga (Caat5–35) and from mangrove sediment (Canv1–58) wereutilized. The strains were identified by using the 16S rRNA gene sequencing asStreptomycessp., related toStreptomyces mimosusspecies. The obtained AgNPswere coded as AgNPs35and AgNPs58and characterized by size andmorphology using dynamic light scattering, zeta potential, transmissionelectron microscopy, and Fourier transformed infrared (FTIR). The antifungalactivity of the AgNPs35and AgNPs58was evaluatedin vitroby the minimalinhibitory concentration (MIC) assay on the phytopathogens,Alternariasolani,Alternaria alternata, andColletotrichum gloeosporioides. The phytotoxiceffect was evaluated by the germination rate and seedling growth of rice(Oryza sativa). AgNPs35and AgNPs58showed surface plasmon resonance andaverage sizes of 30 and 60 nm, respectively. Both AgNPs presented sphericalshape and the FTIR analysis confirmed the presence of functional groups suchas free amines and hydroxyls of biomolecules bounded to the external layer ofthe nanoparticles. Both AgNPs inhibited the growth of the three phytopatho-gens tested, andA. alternatewas the most sensible (MIC≤4 μM). Moreover,the AgNPs35and AgNPs58did not induce phytotoxic effects on thegermination and development of rice seedlings. In conclusion, these AgNPsare promising candidates to biocontrol of these phytopathogens withoutendangering rice plants.