Process optimization for green synthesis of silver nanoparticles by Sclerotinia sclerotiorum MTCC 8785 and evaluation of its antibacterial properties

Abstract

Background: Eco-friendly synthesis of nanoparticles is viewed as an alternative to the chemical method and initiated the use of microorganisms for synthesis. The present study has been designed to utilize plant pathogenic fungi Sclerotinia sclerotiorum MTCC 8785 strain for synthesis and optimization of silver nanoparticles (AgNPs) production as well as evaluation of antibacterial properties. The AgNPs were synthesized by reduction of aqueous silver nitrate (AgNO3) solution after incubation of 3-5 days at room temperature. The AgNPs were further characterized using UV-visible spectroscopy, Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Reaction parameters including media, fungal biomass, AgNO3 concentration, pH and temperature were further optimized for rapid AgNPs production. The antibacterial efficacy of AgNPs was evaluated against Escherichia coli ATCC 25922 and Staphylococcus aureus ATCC 25923 by disc diffusion and growth kinetics assay at the concentration determined by the minimum inhibitory concentration (MIC).

Results: AgNPs synthesis was initially marked by the change in colour from pale white to brown and was confirmed by UV-Vis spectroscopy. Optimization studies showed that potato dextrose broth (PDB) media, 10 g of biomass, addition of 2 mM AgNO3, pH 11 and 80 °C temperature resulted in enhanced AgNPs synthesis through extracellular route. TEM data revealed spherical shape AgNPs with size in the range of 10 nm. Presence of proteins capped to AgNPs was confirmed by FTIR. AgNPs showed antibacterial activity against E. coli and S. aureus at 100 ppm concentration, corresponding MIC value.

Conclusion: S. sclerotiorum MTCC 8785 mediated AgNPs was synthesized rapidly under optimized conditions, which showed antibacterial activity.

Keywords: Antibacterial activity; Green synthesis; Optimization; Sclerotinia sclerotiorum; Silver nanoparticles.

Fig. 1

UV–Vis spectra of AgNPs synthesized using CFF of S. sclerotiorum MTCC 8785. Inset Change in color in CFF after addition of 1 mM AgNO₃ at pH 7 followed by incubation at 30 °C

Fig. 2

UV–Vis spectra of AgNPs synthesis using fungi grown in different media followed by addition of 1 mM AgNO₃ in CFF of 5 gm biomass and incubated in pH 7 at 30 °C

Fig. 3

UV–Vis spectra of AgNPs synthesis using fungi grown in PDB media followed by addition of different concentration of AgNO₃ in CFF of 5 gm biomass and incubated in pH 7 at 30 °C

Fig. 4

UV–Vis spectra of AgNPs synthesis using fungi grown in PDB media followed by addition of 2 mM AgNO₃ in CFF from different fungal biomass and incubated in pH 7 at 30 °C

Fig. 5

UV–Vis spectra of AgNPs synthesis using fungi (10 gm biomass) grown in PDB media followed by incubation in different pH at 30 °C

Fig. 6

UV–Vis spectra of AgNPs synthesis using fungi grown in PDB media followed by addition of 2 mM AgNO₃ in CFF of 10 gm biomass and incubated in pH 11 at different temperature

Fig. 7

TEM images of AgNPs synthesized at 30 °C, pH 7 with 1 mM AgNO₃ at low (a) and high magnification (c). TEM images for AgNPs synthesized at 80 °C, pH 11 with 2 mM AgNO₃ at low (b) and high magnification (d)

Fig. 8

FTIR spectra of a cell free filtrate and b synthesized AgNPs

Fig. 9

Growth profiles of a E. coli and b S. aureus in the presence of varying amounts of AgNPs (25–125 ppm)

Fig. 10

Zone of inhibition at different concentration of AgNPs against A E. coli and B S. aureus. a Cell free filtrate, b 25 ppm, c 50 ppm, d 75 ppm and e 100 ppm of AgNPs, f ampicillin (10 µg/disc) for E. coli and amikacin (30 µg/disc) for S. aureus, g 100 ppm of AgNO₃