Size-Controlled Production of Gold Bionanoparticles Using the Extremely Acidophilic Fe(III)-Reducing Bacterium, Acidocella aromatica

Abstract

Recycling of gold-bearing "urban mine" resources, such as waste printed circuit boards (PCBs), is attracting an increasing interest. Some of the gold leaching techniques utilize acidic lixiviants and in order to eventually target such acidic leachates, the utility of the acidophilic Fe(III)-reducing heterotrophic bacterium, Acidocella (Ac.) aromatica PFBC was evaluated for production of Au (0) bionanoparticles (bio-AuNPs). Au(III) ions (as AuCl 4 − , initially 10 mg/L), were readily adsorbed onto the slightly-positively charged Ac. aromatica cell surface and transported into cytoplasm to successfully form intracellular bio-AuNPs in a simple one-step microbiological reaction. Generally, increasing the initial concentration of formate as e-donor corresponded to faster Au(III) bioreduction and a greater number of Au(0) nucleation sites with less crystal growth within 40-60 h: i.e., use of 1, 5, 10, or 20 mM formate led to production of bio-AuNPs of 48, 24, 13, or 12 nm in mean particle size with 2.3, 17, 62, and 97 particles/cell, respectively. Addition of Cu 2+ as an enzymatic inhibitor significantly decreased the number of Au(0) nucleation sites but enhanced crystal growth of individual particles. As a result, the manipulation of the e-donor concentration combined with an enzyme inhibitor enabled the 3-grade size-control of bio-AuNPs (nearly within a normal distribution) at 48, 26 or 13 nm by use of 1 mM formate, 20 mM formate (+Cu 2+ ) or 10 mM formate, respectively, from highly acidic, dilute Au(III) solutions.

Bacterial Metal Accumulation as a Strategy for Waste Recycling Management

“…Cl also shows intracellular distribution in A. aluminiidurans cells (Figure 4, corresponding elemental map). A study by Rizki et al [67] shows that Acidocella sp. cells are able to rapidly incorporate gold particles into the cell in a matter of minutes, which is consistent with our results of metal incorporation by this microorganism.…”

Biotechnological synthesis of Pd-based nanoparticle catalysts

“…aromatica was shown to reduce Au( iii ) to Au(0) nanoparticles at pH = 2.5. 211 The thermo-acidophilic archaeon Sulfolobus tokodaii was shown to reduce Pd( ii ) from acidic solutions (pH = 2). 212 The archaeon showed increased resistance to chloride concentration, successfully reducing Pd( ii ) in the presence of up to 500 mM Cl − .…”

Biogenic Platinum Nanoparticles’ Production by Extremely Acidophilic Fe(III)-Reducing Bacteria

“…So far, the biological fabrication of metal NPs explored a range of life forms, such as bacteria, yeast, fungi, algae, and plants, for metal species such Au, Ag, Pd, Pt, Ni, Co, and Fe [3,4]. The size of biogenic metal NPs can be controlled by modifying conditions such as concentrations of electron donors and reaction inhibitors [5,6]. Among those microorganisms or plants as the template for NPs' production, a number of bacterial species possess the ability to reduce soluble metal species to zero-valent nanometal.…”

“…Ac. aromatica was also shown to be useful in size-controlled bio-Au(0)NPs' production [6] as well as in reducing soluble V(V) to form V(IV) precipitates in acidic liquors [21]. To the best of our knowledge, the biological synthesis of Pt(0)NPs by extreme acidophiles is not yet known.…”