Rhamnolipids functionalized AgNPs-induced oxidative stress and modulation of toxicity pathway genes in cultured MCF-7 cells
Graphical abstract
Introduction
Development of a reliable, eco-friendly and toxicity-free synthesis of metal nanoparticles (NPs) is an important aspect of nanotechnology research [1]. Lately, the biomimetic and green synthesis of AgNPs using polymer matrices such as starch [2], chitosan [3], cyclodextrins [4], and microbial biomass [5], [6], [7] has been extensively pursued. Microbial synthesis of NPs yields stable particles due to protein capping and interaction with other reducing agents such as nitrate reductase [8], naphthoquinones [9], and anthraquinones [10], secreted by the organisms. Furthermore, synthetic chemicals such as amine and carboxylate surfactants [11], cationic cetylpyridinium, or anionic sodium dodecyl sulphate, or non-ionic Brij 56 [12] have also been used for NPs synthesis. These surfactants are tension-active molecules, amphipathic in nature with both hydrophilic and hydrophobic moieties, and exhibit surface-active properties. With the increasing demand for greener bioprocesses and novel enhancers for NPs synthesis, the biosurfactants, and/or biosurfactant producing microbes are emerging as an alternate source. Thus, biosurfactants with the high surface activity and low critical micelle concentrations (CMC) are regarded as promising substitutes for synthetic surfactants [13]. Several microorganisms like bacteria, fungi, yeasts, and algae are good sources of biosurfactants and offer many advantages over their chemical counterparts. Therefore, the biosurfactant mediated synthesis of NPs is regarded as a clean, non-toxic, and environmentally acceptable “green chemistry” procedure, resulting in reduced NPs aggregation and uniform morphology. Furthermore, the lower toxicity, higher biodegradability, better environmental compatibility, higher foaming, high selectivity and specific activity at extreme temperatures, pH, and salinity [14] are some added advantages over the chemical surfactants.
In this context, the natural rhamnolipids, a subclass of glycolipids produced by bacteria, could serve as simple and economical stabilizer for AgNPs synthesis. Rhamnolipids from Pseudomonas aeruginosa strain BS-161R and its mutant EBN-8 have earlier been used for synthesis of silver NPs (AgNPs) in reverse micelles and composite rhamnolipids-gold NPs microtubules [15], [16]. Pseudomonas species are well known for their capability to produce rhamnolipid biosurfactants on different carbon sources [17], [18]. This has prompted us to develop a simple one-pot method for synthesis of highly stable and dispersible Rh-AgNPs. In this study, we report the role of natural rhamnolipids extracted from the culture supernatant of P. aeruginosa strain JS-11, as a stabilizing agent in synthesis of AgNPs. The synthesized Rh-AgNPs were characterized using the analytical techniques, viz., UV-visible spectrophotometry, XRD spectroscopy, TEM, FTIR and AFM. Rh-AgNPs induced antiproliferative activity and involvement of oxidative stress and toxicity pathways genes have been investigated in human breast adenocarcinoma (MCF7) cells, as an in vitro model.
Section snippets
Bacterial strain characterization and screening for rhamnolipid production
The soil bacteria P. aeruginosa strain JS-11 has been obtained from culture collection of our laboratory [19]. The strain JS-11 was screened for rhamnolipids biosynthesis using the mineral salt-CTAB-methylene blue agar plates, following the method of Inka and Fritz [20]. Briefly, the cell-free culture supernatant (30 μL) was loaded into each pre-cut wells in methylene blue agar plate. The plate was then incubated at 37 °C for 72 h. A dark blue halo zone around the culture was considered as
Synthesis and stability of Rh-AgNPs
The rhamnolipids released by P. aeruginosa strain JS-11 in LB and mineral salt medium containing 4% glucose resulted in decreased surface tension of the medium from 69 mN m−1 to 31 mN m−1, which confirms the presence of biosurfactant in the culture medium. This corroborates with the observations of Rahman et al. [27]. The concentration of the extracted rhamnolipids from the strain JS-11 was determined to be 325 mg/L. The rhamnolipids emulsion in Milli Q water (Supplementary Fig. 1) has been used as
Conflict of interest
There is no conflict of interest.
Acknowledgments
The Chair for DNA research, King Saud University, Riyadh, for this study, is greatly acknowledged. JM is also grateful to the Visiting Professor Program (VPP), King Saud University for all support to carry out this collaborative research.
References (43)
- et al.
Spectroscopic characterization of gold nanoparticles formed by cells and S-layer proteins of Bacillus sphaericus JG-A12
Mater. Sci. Eng.
(2007) - et al.
Morphology and antibacterial activity of carbohydrate-stabilized silver nanoparticles
Carbohydr. Res.
(2010) - et al.
The synthesis of chitosan-based silver nanoparticles and their antibacterial activity
Carbohydr. Res.
(2009) - et al.
Production of antimicrobial silver nanoparticles in water extracts of the fungus Amylomyces rouxii strain KSU-09
Bioresour. Technol.
(2010) - et al.
Biogenic synthesis of silver nanoparticles and their synergistic effect with antibiotics: a study against Gram-positive and Gram-negative bacteria
Nanomedicine
(2010) - et al.
Extracellular biosynthesis of silver nanoparticles using the fungus Fusarium oxysporum
Colloids Surf. B: Biointerfaces
(2003) - et al.
Surfactant-mediated nanoparticle assembly of catalytic mesoporous crystalline iron oxide materials
Catal. Today
(2004) - et al.
Synthesis of silver nanoparticles in reverse micelles stabilized by natural biosurfactant
Colloids Surf. A – Physicochem. Eng. Asp.
(2006) - et al.
Olive oil mill effluent (OOME) new substrate for biosurfactant production
Bioresour. Technol.
(1993) - et al.
Biodegradation of isoproturon using a novel Pseudomonas aeruginosa strain JS-11 as a multi-functional bioinoculant of environmental significance
J. Hazard. Mater.
(2011)