Research articleAn Aspergillus aculateus strain was capable of producing agriculturally useful nanoparticles via bioremediation of iron ore tailings
Introduction
Iron ore tailings are abundant environmental contaminant from mining sites. World iron ore resources are estimated to be greater than 800 billion tons with more than 230 billion tons of iron (https://minerals.usgs.gov). Brazil is the largest producer of iron ore followed by China, Australia, India and Russia, with these countries in particular having mining contamination problems. About 3220 MT of iron ore was produced globally during 2014, with generation of huge amounts of mining waste. This waste is primarily stored in large impoundments known as tailing dams and is not effectively remediated.
The concentration and availability of metals in the polluted environment in and around mines and other polluting industries, along with the nature of metals and temperature, affect the microbial population living in those conditions. Some fungi are known to thrive in these stressed conditions, as they can tolerate extreme temperature, pH and metal concentrations (Baldrian, 2003; Gavrilescu, 2004; Milova-Ziakova et al., 2016). Some of these fungi have the ability to convert the metal waste material into nanoparticles, thereby neutralising their toxic effects. There are several reports on fungi being applied as bioleaching agents to dissolve metals from waste materials (Bosshard et al., 1996; Dacera and Babel, 2008; Khan et al., 2014; Madrigal-Arias et al., 2015), ores (Biswas et al., 2013; Mishra and Rhee, 2014; Mulligan et al., 2004) and minerals (Amiri et al., 2011; Anjum et al., 2010; Brisson et al., 2016; Hosseini et al., 2007). According to these studies, organic acids such as citric acid, oxalic acid and gluconic acid, exogenously produced by the fungus, can help in the leaching of metals due to their chelating or reducing abilities. This ability of microbes to tolerate high metal ion concentrations and convert this metal waste into nanoparticles, has encouraged scientists to use these microbes as eco-friendly nanofactories for the biological synthesis of nanoparticles (Duran et al., 2005; Khan et al., 2014). Some Aspergillus strains have been shown to be resistant to high metal concentrations by modifying their metabolic activities to tolerate these metals (Chakraborty et al., 2013; Kumari et al., 2015; Santhiya and Ting, 2005; Seh-Bardan et al., 2012).
Myconanomining (Fungi mediated bioleaching and conversion of bulk metallic elements/compounds into nanostructures) is considered safe and ecologically benign for the conversion of bulk inorganic (metal based) materials into nanostructured forms. The use of this myconanomining approach for bioleaching and biosynthesis of nanoparticles from tailings waste offers several advantages over other environmental biological process, such as: (i) Higher biomass production; (ii) fungal secretome contains large amounts of extracellular proteins with diverse functions; (iii) more biosorption of metallic elements/compounds at low pH; and (iv) high metal reducing activity of secretome. Here, the fungal biomass aqueous extract containing secretome is used for bioleaching from collected iron ore tailings, with the subsequent biosynthesis of nanoparticles for use as plant nutrient Fe.
In this study we isolated several new strains from contaminated iron ore tailing of mining sites and discovered a new strain of Aspergillus aculeatus (strain T6) that efficiently converts iron ore tailings into nanoparticles. These particles were then applied to a model plant growth system (mungbean seeds) and show to seed emergence activity.
Section snippets
Materials used
All chemicals used in this study were purchased from Fischer Scientific (Mumbai, India) and were of analytical grade. Potato dextrose agar, Potato dextrose broth, Mycological peptone, Agar Extra pure used were procured from HiMedia (Mumbai, India) and were sterilized by autoclaving at 120 °C for 15 min at 15 psi before use. Mungbean (Vigna radiata) seeds (Type 44 variety) was purchased locally.
Iron ore tailings collection and analysis
Iron ore tailings (brick red in color) were collected from Codli mines, Goa, India (24°35′58″N
Elemental analysis and particle size imaging of iron ore tailings
The metal content of the collected iron ore tailings was determined using AAS (Table 1) and the morphological characteristics by TEM. Iron was the most abundant metal (∼42,000 ppm), followed by aluminium (∼34,000 ppm). Our results show lower iron proportionately to other metals, compared with previous studies, although some variation with location is expected (Ilyas et al., 2013; Pappu et al., 2011).
TEM showed an aggregated crystalline structure with irregularly shaped amorphous particles with
Conclusion
In this study, bioleaching from tailings waste, using a cell-free extract of A. aculeatus strain T6, was carried out and the formation of protein capped NPs was observed. A fall in pH of cell-free extract during fermentation indicated the release of organic acids, which are at least partially responsible for the bioleaching from these wastes. The biologically synthesized NPs stabilized in solution due to the protein coating matrix. The biosynthesized NPs were investigated as a source of
Acknowledgement
We acknowledge Ms. Deeprajni for HPLC, Ms. Shikha for SEM, Mr. Ranjit and Mr. Palak for AAS and Mr. Chandrakant and Mr. Aditya for TEM analysis. Dr. Sashidhar and Ms. Richa are also acknowledged for assisting in molecular work. The PhD Scholarship provided to AB by Deakin University, Australia and infrastructure support extended by The Energy and Resources Institute, India is also acknowledged.
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