Biosynthesis of Stable Antioxidant ZnO Nanoparticles by <i>Pseudomonas aeruginosa</i> Rhamnolipids

<div><p>During the last several years, various chemical methods have been used for synthesis of a variety of metal nanoparticles. Most of these methods pose severe environmental problems and biological risks; therefore the present study reports a biological route for synthesis of zinc oxide nanoparticles using <i>Pseudomonas aeruginosa</i> rhamnolipids (RLs) (denoted as <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a>) and their antioxidant property. Formation of stable <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles gave mostly spherical particles with a particle size ranging from 35 to 80 nm. The <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles were characterized by UV-visible (UV–vis) spectroscopy, scanning electron microscopy, transmission electron microscopy, dynamic light scattering, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), and thermal gravimetric analysis. The UV–vis spectra presented a characteristic absorbance peak at ∼360 nm for synthesized <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles. The XRD spectrum showed that <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles are crystalline in nature and have typical wurtzite type polycrystals. Antioxidant potential of <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles was assessed through 2,2–diphenyl-1-picrylhydrazyl (DPPH), hydroxyl, and superoxide anion free radicals with varying concentration and time of the storage up to 15 months, while it was found to decline in bare ZnO nanoparticles. Similarly, the inhibitory effects on β-carotene oxidation and lipid peroxidation were also observed. These results elucidate the significance of <i>P</i>. <i>aeruginosa</i> RL as effective stabilizing agents to develop surface protective ZnO nanoparticles, which can be used as promising antioxidants in biological system.</p></div

Characterization of RL@ZnO nanoparticles.

<p>(A) UV–vis spectra of <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles (orange line) and RL (black line). A characteristic absorption peak of <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles (10 µg/mL) was recorded at ∼A₃₆₀ nm wavelength. (B) XRD pattern of <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles for a typical wurtzite type polycrystals and particle size was found to be ∼27 nm. (C) SEM image of <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles demonstrates clearly the formation of aggregation of ZnO nanoparticles. (D) EDX image of <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles indicates the presence of zinc and oxygen molecules only.</p

Biofabricated Silver Nanoparticles Act as a Strong Fungicide against <i>Bipolaris sorokiniana</i> Causing Spot Blotch Disease in Wheat

<div><p>The present study is focused on the extracellular synthesis of silver nanoparticles (AgNPs) using culture supernatant of an agriculturally important bacterium, <i>Serratia</i> sp. BHU-S4 and demonstrates its effective application for the management of spot blotch disease in wheat. The biosynthesis of AgNPs by <i>Serratia</i> sp. BHU-S4 (denoted as bsAgNPs) was monitored by UV–visible spectrum that showed the surface plasmon resonance (SPR) peak at 410 nm, an important characteristic of AgNPs. Furthermore, the structural, morphological, elemental, functional and thermal characterization of bsAgNPs was carried out using the X-ray diffraction (XRD), electron and atomic microscopies, energy dispersive X-ray (EDAX) spectrometer, FTIR spectroscopy and thermogravimetric analyzer (TGA), respectively. The bsAgNPs were spherical in shape with size range of ∼10 to 20 nm. The XRD and EDAX analysis confirmed successful biosynthesis and crystalline nature of AgNPs. The bsAgNPs exhibited strong antifungal activity against <i>Bipolaris sorokiniana</i>, the spot blotch pathogen of wheat. Interestingly, 2, 4 and 10 µg/ml concentrations of bsAgNPs accounted for complete inhibition of conidial germination, whereas in the absence of bsAgNPs, conidial germination was 100%. A detached leaf bioassay revealed prominent conidial germination on wheat leaves infected with <i>B. sorokiniana</i> conidial suspension alone, while the germination of conidia was totally inhibited when the leaves were treated with bsAgNPs. The results were further authenticated under green house conditions, where application of bsAgNPs significantly reduced <i>B. sorokiniana</i> infection in wheat plants. Histochemical staining revealed a significant role of bsAgNPs treatment in inducing lignin deposition in vascular bundles. In summary, our findings represent the efficient application of bsAgNPs in plant disease management, indicating the exciting possibilities of nanofungicide employing agriculturally important bacteria.</p></div

Molecular characterization of <i>P</i>. <i>aeruginosa</i> CEMS077.

<p>Phylogenetic tree showing relationship of CEMS077 with other strains of <i>Pseudomonas</i> species based on 16S rRNA gene sequences retrieved from NCBI GenBank. Arrow represents the status of strain CEMS077 from this study in phylogenetic tree.</p

Characterization of RL@ZnO nanoparticles.

<p>(A) The representative TEM microphotographs of bare ZnO nanoparticles (a) and <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles (b) at an accelerating voltage of ∼200 kV. Inset of the figure (b) depicts the particle size analysis. (B) Band gap plot of <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles, calculated by Tauc plot formula. (C) FTIR spectra of RL extract (red line) and <a href="mailto:RL@ZnO" target="_blank">RL@ZnO</a> nanoparticles (black line). The spectra shown are representatives of the three independent experiments.</p

Biosynthesis of AgNPs by supernatant of <i>Serratia</i> sp. BHU-S4 (A).

<p>Culture supernatant without 1₃ showed no color change (C) and after adding 1 mM AgNO₃ showed visual color change from yellow to dark brown. (B) UV-visible absorption spectrum of bsAgNPs and 1 mM aqueous solution of AgNO₃.</p

EDAX spectrum (A), FTIR spectrum (B) and TGA graph (C) of bsAgNPs by <i>Serratia</i> sp. BHU-S4.

<p>EDAX spectrum (A), FTIR spectrum (B) and TGA graph (C) of bsAgNPs by <i>Serratia</i> sp. BHU-S4.</p