Proteomics study of silver nanoparticles toxicity on Bacillus thuringiensis

Highlights

• Study the Silver Nanoparticle, (AgNPs), toxicity on soil beneficial bacteria.

• Evaluate the proteins pattern of B. thuringiensis, (Bt), AgNPs treated.

• Study the mechanism of Bt toxicity from proteomics points of view.

Abstract

Emerging technologies in functional genomics and proteomics provide a way of achieving high-throughput analyses, understanding effects on protein populations and sub-populations and follow up environmental stresses. To accomplish these, the action of homemade spherical Silver nanoparticles colloidal suspension (AgNPs) against Bacillus thuringiensis (isolate from Oryza sativa L. rhizosphere) was investigated by a proteomic approach (2-DE and NanoLC/FT-ICR MS identification). Thirty four responsive (up/down regulated) proteins were identified. Proteomic results revealed that an exposure of B. thuringiensis cells with different concentrations of AgNPs resulted in an accumulation of envelope protein precursors, indicative of the dissipation of a proton motive force. Identified proteins are involved in oxidative stress tolerance, metal detoxification, transcription and elongation processes, protein degradation, cytoskeleton remodeling and cell division. The expression pattern of these proteins and their possible involvement in the nontoxicity mechanisms were discussed.

Introduction

It has been discovered that silver and its related compounds are effective anti-microbial agents. They have a variety of applications including a prophylactic effect for human infections, the treatment of wounds and on plant and animal microbial diseases (Navarro et al., 2008). Silver nanoparticles (AgNPs) as a newborn form of silver represent a novel generation of anti-microbial, anti-fungal and anti-viral applications against a very broad range of microorganisms (Kim et al., 2008, Rai et al., 2009). Environmental pollution caused by AgNPs, particularly contamination of soil and water resources, has been accelerated as a result of global industrialization and is considered a major risk for communities throughout the world (Navarro et al., 2008).

Soil ecosystems have been exposed to toxic compounds, among which are AgNPs (Filip, 2002). Some of the soil bacteria communities have an outstanding ability to adapt to a polluted environment according to employ various unique mechanisms (Wang et al., 2007). Consequently, polluted soil is faced with new kinds of micro flora; some have changed significantly, others are simply missing. Several negative effects on soil beneficial bacteria, suggesting that they have adverse reactions to pollution such as nanoparticles (Filip, 2002, Wang et al., 2007). Bacillus thuringiensis (Bt) is a Gram-positive soil-dwelling bacterium, commonly used as a biological pesticide. Its cry toxin is extracted and used as a pesticide. Many Bt strains produce crystal proteins (proteinaceous inclusions), called δ-endotoxins, that have insecticidal action. This compound has led to their use as an insecticide, and Bt genes are used to genetically modify crops recently (Höfte and Whiteley, 1989).

A bacterial cell can react simultaneously to a wide variety of stresses (Vollmer et al., 2008). Stress response mechanism of bacteria enables them to survive adverse and mutable conditions in their immediate environments. Various mechanisms have been suggested to bacterial responses following the different environmental fluctuations. The stress response in bacteria involves a number of systems that act against an external stimulus. A complex network of global regulatory systems in bacteria certifies that various stress response systems interact with each other and this leads to a coordinated and effective response.

Proteomics is a fastest developing field of research and it contributes substantially to our understanding of organisms at the cellular level (Lok et al., 2006, Navarro et al., 2008). In addition, this is the study of functions and regulation of biological systems based on analysis of the protein expression profile. Furthermore, there is general agreement that soil bacterial proteomics may be a tool for its better management. Because of the ability of soil to stabilize extracellular proteins over various mechanisms, development of bacterial proteomics needs an assessment of the efficiency of protein extraction from various soil types. In the case of nanotechnology environment proteomics Li et. al. used the gel-base proteomics together with other biochemical studies to evaluate the AgNPs action on Staphylococcus aureus (Li et al., 2011). The aim of this study was to evaluate the action of homemade spherical colloidal AgNPs suspension against Bacillus thuringiensis (isolate from Oryza sativa L. rhizosphere) from proteomic point of view using the gel-base combined NanoLC/FT-ICR MSMS method.