The effect of Plant Growth Promoting Rhizobacteria (Bacillus sp.) and silver nanoparticles on Zea mays was evaluated. The silver nanoparticles were synthesized from Tagetes erecta (Marigold) leaf and flower extracts, whereas PGPR isolated from spinach rhizosphere. The silver nanoparticles (AgNPs) were purified using ultra centrifugation and were characterized using UV–Vis spectroscopy at gradient wavelength and also by High Resolution Transmission Electron microscopy (HRTEM). The average particles size of AgNPs was recorded approximately 60 nm. Almost all potential isolates were able to produce Indole Acetic Acid (IAA), ammonia and Hydrogen cyanide (HCN), solubilized tricalcium phosphate and inhibited the growth of Macrophomina phaseolina in vitro but the isolate LPR2 was found the best among all. On the basis of 16S rRNA gene sequence, the isolate LPR2 was characterized as Bacillus cereus LPR2. The maize seeds bacterized with LPR2 and AgNPs individually showed a significant increase in germination (87.5%) followed by LPR2 + AgNPs (75%). But the maximum growth of root and shoot of maize plant was observed in seeds coated with LPR2 followed by AgNPs and a combination of both. Bacillus cereus LPR2 and silver nanoparticles enhanced the plant growth and LPR2 strongly inhibited the growth of deleterious fungal pathogen. Therefore, LPR2 and AgNPs could be utilized as bioinoculant and growth stimulator, respectively for maize.

In the present study, gold (AuNPs) and gold-silver bimetallic nanoparticles (Au-Ag BMNPs) were fabricated by using water extract of leaves of Triticum aestivum - a crop plant, and their bactericidal potency was checked against selected pathogenic bacterial strains. The phytofabricated AuNPs and BMNPs were analyzed for their physical attributes using UV–Visible and Fourier transformed infrared spectroscopy, Dynamic light scattering, High-resolution transmission electron microscopy, Energy-dispersive X-ray spectroscopy. HRTEM analysis revealed that both kinds of NPs were highly crystalline in nature and of spherical and oval-shaped. AuNPs size was found in the range of 5-40 nm, whereas BMNPs showed their size in the range of 5-30 nm. HRTEM results were corroborated by DLS results which revealed the average hydrodynamic diameter of AuNPs and BMNPs in the range of 29.08 and 26.56 nm, respectively. UV-visible spectroscopy showed high-intensity single spectral peaks at 540 and 480 nm for AuNPs and BMNPs, respectively. FTIR analysis demonstrated that protein, flavanones, hydroxyl, carboxylate groups, and reducing sugars were responsible for reducing and capping of both NPs. Bactericidal efficiency of synthesized NPs was evaluated using agar-well diffusion and XTT-colorimetric assays against K. pneumoniae, S. typhimurium, E. aerogenes, E. coli, M. luteus, S. aureus, S. mutans and S. epidermidis. K. pneumonia and S. typhimurium were found to be the most sensitive bacteria towards BMNPs-mediated (MIC: 400 µg/ml) and AuNPs-mediated toxicity (MIC: 800 µg/ml). It was observed that BMNPs generally possessed more powerful bactericidal effect against all bacterial strains in comparison to AuNPs. MIC and MBC values were observed in the concentration range of 400 µg/ml-1.5 mg /ml for different bacterial strains. Furthermore, it was demonstrated that phytosynthesized AuNPs have their own bactericidal effect, but at higher concentrations (>100 µg/ml), and bactericidal effect of BMNPs was due to the synergistic effect of both Ag and Au ions, which was also observed to be concentration-dependent.

The application of silver nanoparticles (AgNPs)-based antibacterial therapeutics has emerged as a feasible alternative to traditional antibiotic therapy due to cost-effectiveness and lower possibility of non-evolution of resistant strains. In the present paper, the aqueous extract of wheat (Triticum aestivum) and rice (Oryza sativa) leaflets were used for the fabrication of well-dispersed AgNPs of average size 19.11 and 33.85 nm, respectively, under the controlled condition of pH 10.0 + 0.1 and temperature 80°C + 1°C. This bottom-up approach of AgNPs production was simple, eco-friendly, inexpensive, and highly reproducible. The synthesized AgNPs were characterized by UV-Visible spectroscopy, dynamic light scattering, fourier transform infrared spectroscopy, high-resolution transmission electron microscopy, and energy-dispersive X-ray. Agarwell diffusion and (2, 3-bis [2-methyloxy-4-nitro-5-sulfophenyl]-2H-tetrazolium-5-carboxanilide) (XTT) colorimetric methods revealed the bactericidal potential of synthesized AgNPs against Gram-positive and Gram-negative pathogenic bacteria with minimum inhibitory concentration (MIC) values ranges from 125 to 500 µg/ml. AgNPs presented better potency against Gram-negative bacteria compared to Gram-positive bacteria. Interestingly, Staphylococcus aureus, Klebsiella pneumoniae, and Escherichia coli demonstrated a hormetic response (positive stimulated growth) at a sub-lethal concentration (<7.81 µg/ml) of AgNPs, which were 0.39%-1.56% of MIC values of the respective bacterial strains.