Silver Nanoparticles Synthesized by Using Bacillus cereus SZT1 Ameliorated the Damage of Bacterial Leaf Blight Pathogen in Rice

Abstract

Amongst serious biotic factors deteriorating crop yield, the most destructive pathogen of rice is Xanthomonas oryzae pv. oryzae (Xoo), which causes bacterial leaf blight (BLB) disease. This study involved targeted use of biogenic silver nanoparticles (AgNPs) to control BLB in order to cope with the disadvantages of chemical disease control. AgNPs were biologically synthesized from natively isolated Bacillus cereus strain SZT1, which was identified through 16S rRNA gene sequence analysis. Synthesis of AgNPs in bacterial culture supernatant was confirmed through UV-VIS spectroscopy. Fourier transform infrared spectroscopy (FTIR) confirmed that the existence of AgNPs was stabilized with proteins and alcoholic groups. X-ray diffraction (XRD) data revealed the crystalline nature and imaging with scanning electron microscopy (SEM) and transmission electron microscopy (TEM), showing the spherical shape of AgNPs with particle sizes ranging from 18 to 39 nm. The silver presence in AgNPs was further confirmed by energy dispersive spectra. Biogenic AgNPs showed substantial antibacterial activity (24.21 ± 1.01 mm) for Xoo. In a pot experiment, AgNPs were found to be effective weapons for BLB by significantly increasing the plant biomass with a decreased cellular concentration of reactive oxygen species and increased concentration of antioxidant enzyme activity.

Keywords: B. cereus; BLB; antimicrobial activity; nanotechnology; rice; silver nanoparticles.

Figure 1

Growth curves of B. cereus SZT1 in the presence of different AgNO₃ concentrations.

Figure 2

Phylogenetic tree of B. cereus SZT1 with the type strains of genus Bacillus. The evolutionary history was inferred using the maximum likelihood (ML) method. The percentages (≥50%) of replicate trees in which the associated taxa clustered together in the bootstrap test (1000 replicates) are shown. Evolutionary distances were computed using the Timura–Nei model and are in units of the number of base substitutions per site.

Figure 3

Antibacterial activity of silver nanoparticles (AgNPs) synthesized from B. cereus SZT1 in various concentrations against Xanthomonas oryzae pv. oryzae (Xoo). (a) measurement of antibacterial activity through well-diffusion assay; (b) measurement of antibacterial activity through inhibition of bacterial cell density.

Figure 4

UV-VIS spectrum of cell free supernatant containing biogenic AgNPs synthesized by using B. cereus SZT1 after 24 h. The absorption spectrum of biogenic AgNPs showed a strong peak at 418.99 nm.

Figure 5

Characterization of the biogenic AgNPs synthesized from B. cereus SZT1. (a) FTIR spectra of the biogenic AgNPs synthesized from B. cereus SZT1 in the wavelength range of 350-4000 cm⁻¹; (b) XRD spectrum of biogenic AgNPs synthesized from B. cereus SZT1.

Figure 6

Characterization of the biogenic AgNPs synthesized from B. cereus SZT1. (a) Transmission electron microscopy; (b) scaning electron microscopy; (c) EDS spectrum.