Biogenic Synthesis of Silver Nanoparticles Using Phyllanthus emblica Fruit Extract and Its Inhibitory Action Against the Pathogen Acidovorax oryzae Strain RS-2 of Rice Bacterial Brown Stripe.

Md Mahidul Islam Masum,Yang Zhang,Yasmine Abdallah,Chenqi Yan,Ezzeldin Ibrahim,Wen Qiu,Bin Li,Khattak Arif Ali,Mst Mahfuja Siddiqa

doi:10.3389/fmicb.2019.00820

Abstract

Biogenic synthesis of silver nanoparticles (AgNPs) using plants has become a promising substitute to the conventional chemical synthesis method. In this study, we report low-cost, green synthesis of AgNPs using fresh fruit extract of Phyllanthus emblica. The biosynthesized AgNPs was confirmed and characterized by analysis of spectroscopy profile of the UV-visible and Energy dispersive spectrophotometer, Fourier transform infrared, X-ray diffraction pattern, and electron microscopy images examination. UV-visible spectra showed a surface resonance peak of 430 nm corresponding to the formation of AgNPs, and FTIR spectra confirmed the involvement of biological molecules in AgNPs synthesis. In spherical AgNPs, the particle size ranged from 19.8 to 92.8 nm and the average diameter was 39 nm. Synthesized nanoparticles at 20 μg/ml showed remarkable antimicrobial activity in vitro against the pathogen Acidovorax oryzae strain RS-2 of rice bacterial brown stripe, while 62.41% reduction in OD600 value was observed compared to the control. Moreover, the inhibitory efficiency of AgNPs increased with the increase of incubation time. Furthermore, AgNPs not only disturbed biofilm formation and swarming ability but also increased the secretion of effector Hcp in strain RS-2, resulting from damage to the cell membrane, which was substantiated by TEM images and live/dead cell staining result. Overall, this study suggested that AgNPs can be an attractive and eco-friendly candidate to control rice bacterial disease.

Highlights

In recent decades, the development of new and effective antimicrobials against infections caused by antibiotic-resistant bacteria has been increasingly interested
The synthesis of AgNPs in the solution was confirmed by the results of UV-visible spectrophotometers, which exhibited a spectrum of surface plasmon resonance (SRP) ranging from 430 to 436 nm of absorption band (Figure 2B)
Results of the Enzyme-linked immune sorbent assay (ELISA) showed that Acidovorax oryzae (Ao) strain RS-2 treated with AgNPs caused increased secretion of Hcp protein as compared to the control.These results are pretty congruent with the observations of Dong et al, 2016), who reported that camptothecin, a monoterpenoid indole alkaloid antimicrobial compound, caused the up-regulated expression of hcp and the increased secretion of Hcp in live Ao strain RS-2 detected on ELISA analysis

Summary

Introduction

The development of new and effective antimicrobials against infections caused by antibiotic-resistant bacteria has been increasingly interested. Previous studies have demonstrated that AgNPs have potential antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Serratia marcescens (Kim et al, 2007; Oves et al, 2013; Aziz et al, 2016). Several methods have been described for the synthesis of AgNPs, such as chemical reduction, microemulsions, radiation, hybrid methods, photochemical reduction and sonoelectrochemical, microwave-based systems and recently green synthesis route (Socol et al, 2002; Solanki and Murthy, 2010; Nadagouda et al, 2011; Iravani et al, 2014). Green synthesis route of AgNPs using several microorganisms, plants, and algae is natural, biocompatible, and environmentally safe methods (Bhattacharya and Gupta, 2005; Mohanpuria et al, 2008; Aziz et al, 2015)

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