A nonspecific synergistic effect of biogenic silver nanoparticles and biosurfactant towards environmental bacteria and fungi

Chojniak Joanna,Płaza Grażyna,Libera Marcin,Król Ewa

doi:10.1007/s10646-018-1899-3

Abstract

The present study focused on the evaluation of a nonspecific synergistic effect of biogenic silver nanoparticles (AgNPs) in combination with biosurfactants against environmental bacteria and fungi. The AgNPs were synthesized in the culture supernatants of the biosurfactant producer Bacillus subtilis grown in brewery effluent, molasses or Luria-Bertani media. Antibacterial activities were tested against Gram-positive and Gram-negative bacteria, while the antifungal activity was tested against phytopathogens. The interactions between biogenic AgNPs and DNA were investigated using a cryo-TEM technique. The presence of biosurfactant significantly increased the stability of biogenic AgNPs and enhanced their antimicrobial activities. The physical properties and antimicrobial activity of biogenic AgNPs were compared with chemically synthesized Ag nanoparticles. Biogenic silver nanoparticles showed a broad spectrum of activity against bacteria and fungi. They were most active against phytopathogenic fungi and Gram-positive bacteria and less active against Gram-negative bacteria. The nonspecific synergistic effect of biogenic AgNPs and biosurfactant on the phytopathogenic fungi was especially observed. In this report, the new roles of biosurfactants as a biogenic AgNPs stabilizer and enhancer of their antimicrobial properties are presented. Our results revealed that the biologically synthesized AgNPs by the biosurfactant-producing bacterium Bacillus subtilis grown on agro-industrial wastes, such as molasses and brewery effluent, could be used as a promising new nanoagent against microbes.

Highlights

Nanobiotechnology has recently emerged as an area of interest a result of an active integration between microbial biotechnology and nanotechnology
The antibacterial activity of biosynthesized AgNPs was found to be highly effective against Gram-positive bacteria, whereas the antibacterial activity against Gram-negative was found to be mild
The highest antimicrobial activity of the biogenic AgNPs was observed against Paenibacillus bercinonensis and Micrococcus luteus (Fig. 1a) The maximum zones of inhibition diameters were 14 and 16 mm for Paenibacillus bercinonensis and Micrococcus luteus, respectively

Summary

Introduction

Nanobiotechnology (bionanotechnology, nanobiology) has recently emerged as an area of interest a result of an active integration between microbial biotechnology and nanotechnology. The biosynthesis of metal nanoparticles (MeNPs) has been developed as an alternative, environmentally benign nanobiotechnological method. Recognizing the importance of developing eco-friendly methods for the synthesis of biologically active nanoparticles, scientists have recently started looking into research relating to the synthesis of metallic nanoparticles with the additional use of biosurfactants as capping agents (Kiran et al 2010; Reddy et al 2009a; Reddy et al 2009b; Singh et al 2011). It was observed that biosurfactants produced by microorganisms can play a very important role in the process of metallic nanoparticle aggregation and stabilization. One of the biosurfactant modes of action is through adsorbing onto metallic nanoparticles (MeNPs), surface-stabilizing the nanoparticles and preventing subsequent aggregation (Chen and Yeh 2002; Kvitek et al 2008).

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Results

Conclusion