Antimicrobial Activity and Mechanism of Inhibition of Silver Nanoparticles against Extreme Halophilic Archaea - PubMed (original) (raw)

Antimicrobial Activity and Mechanism of Inhibition of Silver Nanoparticles against Extreme Halophilic Archaea

Rebecca S Thombre et al. Front Microbiol. 2016.

Abstract

Haloarchaea are salt-loving halophilic microorganisms that inhabit marine environments, sea water, salterns, and lakes. The resistance of haloarchaea to physical extremities that challenge organismic survival is ubiquitous. Metal and antibiotic resistance of haloarchaea has been on an upsurge due to the exposure of these organisms to metal sinks and drug resistance genes augmented in their natural habitats due to anthropogenic activities and environmental pollution. The efficacy of silver nanoparticles (SNPs) as a potent and broad spectrum inhibitory agent is known, however, there are no reports on the inhibitory activity of SNPs against haloarchaea. In the present study, we have investigated the antimicrobial potentials of SNPs synthesized using aqueous leaf extract of Cinnamomum tamala against antibiotic resistant haloarchaeal isolates Haloferax prahovense RR8, Haloferax lucentense RR15, Haloarcula argentinensis RR10 and Haloarcula tradensis RR13. The synthesized SNPs were characterized by UV-Vis spectroscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy, dynamic light scattering, X-ray diffraction and Fourier transform infrared spectroscopy. The SNPs demonstrated potent antimicrobial activity against the haloarchaea with a minimum inhibitory concentration of 300-400 μg/ml. Growth kinetics of haloarchaea in the presence of SNPs was studied by employing the Baranyi mathematical model for microbial growth using the DMFit curve fitting program. The C. tamala SNPs also demonstrated cytotoxic activity against human lung adenocarcinoma epithelial cell line (A540) and human breast adenocarcinoma cell line (MCF-7). The mechanism of inhibition of haloarchaea by the SNPs was investigated. The plausible mechanism proposed is the alterations and disruption of haloarchaeal membrane permeability by turbulence, inhibition of respiratory dehydrogenases and lipid peroxidation causing cellular and DNA damage resulting in cell death.

Keywords: Baranyi model; Cinnamomum tamala; antibiotic resistant; antimicrobial; cytotoxicity; extreme haloarchaea; membrane permeability; silver nanoparticles.

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Figures

FIGURE 1

FIGURE 1

(A) UV-Vis spectra of SNP synthesized using C. tamala extract; inset figure: color change from pale yellow (0 h) to dark brown (5 h) indicating synthesis of nanoparticles. (B) FEG-SEM of SNPs synthesized using C. tamala leaf extract depicting spherical nanoparticles. (C) Energy Dispersive X-ray spectrum of SNPs biosynthesized using C. tamala leaf extract. (D) Fourier transform infrared spectra of SNPs synthesized using C. tamala leaf extract.

FIGURE 2

FIGURE 2

Growth curve of Haloarchaea in different concentrations of SNPs: (A)Haloarcula argentinensis, (B)Haloarcula tradensis, (C)Haloferax lucentense, and (D)Haloferax prahovense.

FIGURE 3

FIGURE 3

Effect of SNPs on membrane leakage of reducing sugars in haloarchaea (A)Haloarcula argentinensis, (B)Haloarcula tradensis, (C)Haloferax lucentense, and (D)Haloferax prahovense. Error bar represents standard error.

FIGURE 4

FIGURE 4

Effect of SNPs on membrane leakage of proteins in haloarchaea (A)Haloarcula argentinensis, (B)Haloarcula tradensis, (C)Haloferax lucentense, and (D)Haloferax prahovense. Error bar represents standard error.

FIGURE 5

FIGURE 5

Effect of SNPs on respiratory chain dehydrogenase activity in haloarchaea (A)Haloarcula argentinensis, (B)Haloarcula tradensis, (C)Haloferax lucentense, and (D)Haloferax prahovense.

FIGURE 6

FIGURE 6

Effect of SNPs on membrane lipid peroxidation as detected by MDA content in haloarchaea (A)Haloarcula argentinensis, (B)Haloarcula tradensis, (C)Haloferax lucentense, and (D)Haloferax prahovense. Error bar represents standard error.

FIGURE 7

FIGURE 7

Proposed mechanism of inhibition of haloarchaea by SNPs. (A) Attachment of SNPs to cell. [1: SNPs, 2: Bacteriorhodopsin protein, 3: Electron transport chain, 4: ATPase complex, 5: Trk type Potassium ion channel, 6: Haloarchaeal genomic DNA, 7: S-layer, 8: Membrane, 9: Intracellular cytosol]. (B) Disruption of membrane integrity and leakage of intracellular constituents. (C) Inhibition of respiratory dehydrogenases and electron transport chain and generation of MDA and ROS. (D) Oxidative, DNA and cellular damage caused by ROS leading to cell death.

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