83 research outputs found
Bio-nanotechnology application in wastewater treatment
The nanoparticles have received high interest in the field of medicine and water purification, however, the nanomaterials produced by chemical and physical methods are considered hazardous, expensive, and leave behind harmful substances to the environment. This chapter aimed to focus on green-synthesized nanoparticles and their medical applications. Moreover, the chapter highlighted the applicability of the metallic nanoparticles (MNPs) in the inactivation of microbial cells due to their high surface and small particle size. Modifying nanomaterials produced by green-methods is safe, inexpensive, and easy. Therefore, the control and modification of nanoparticles and their properties were also discussed
The biogeochemistry of gold
The biosphere catalyzes a variety of biogeochemical reactions that can transform gold. Microbial weathering contributes to the mobilization of gold by releasing elemental gold trapped within minerals and by solubilizing gold via oxidation-promoting complexation. Subsequent microbial destabilization of gold complexes coupled with bioprecipitation and biomineralization can immobilize gold, completing the cycle. Secondary gold can occur as colloidal particles, crystalline gold and bacteriomorphic structures, the latter being a controversial form of `biogenic' gold.Gordon Southam, Maggy F. Lengke, Lintern Fairbrother and Frank Reit
Floating gold grains and nanophase particles produced from the biogeochemical weathering of a gold-bearing ore
A gold-bearing ore from the San Salvador vein, Capillitas mine, Argentina, was exposed to an enriched, iron- and sulfur-oxidizing bacterial consortium for two months in an experimental system that represented an oxidized, acid-leached weathering environment. Within this laboratory model, the dissolution of metal sulfide minerals by the bacterial consortium liberated gold grains that floated on water. Surficial crevices on grains contained detrital material associated with μm-scale, gold-rich bacteriomorphic structures interpreted to be relics of gold dissolution. The presence of nanophase gold particles, i.e., colloids and octahedral platelets, was attributed to gold reprecipitation. These secondary gold structures suggest that gold dissolution/reprecipitation, i.e., cycling, was occurring concurrently with the bacterially catalyzed dissolution of metal sulfides. The flake-like morphology and small size of gold grains, i.e., high surface area to volume ratio increased by μm-scale surface dissolution textures, would have enhanced their propensity to float. The liberation of buoyant gold grains and secondary gold particles could contribute to rapid gold mobility and dispersion in natural environments.Jeremiah Shuster, Maggy Lengke, María Florencia Márquez-Zavalía, Gordon Southa
Mechanisms of gold biomineralization in the bacterium Cupriavidus metallidurans
While the role of microorganisms as main drivers of metal mobility and mineral formation under Earth surface conditions is now widely accepted, the formation of secondary gold (Au) is commonly attributed to abiotic processes. Here we report that the biomineralization of Au nanoparticles in the metallophillic bacterium Cupriavidus metallidurans CH34 is the result of Au-regulated gene expression leading to the energy-dependent reductive precipitation of toxic Au(III)-complexes. C. metallidurans, which forms biofilms on Au grains, rapidly accumulates Au(III)-complexes from solution. Bulk and microbeam synchrotron X-ray analyses revealed that cellular Au accumulation is coupled to the formation of Au(I)-S complexes. This process promotes Au toxicity and C. metallidurans reacts by inducing oxidative stress and metal resistances gene clusters (including a Au-specific operon) to promote cellular defense. As a result, Au detoxification is mediated by a combination of efflux, reduction, and possibly methylation of Au-complexes, leading to the formation of Au(I)-C-compounds and nanoparticulate Au0. Similar particles were observed in bacterial biofilms on Au grains, suggesting that bacteria actively contribute to the formation of Au grains in surface environments. The recognition of specific genetic responses to Au opens the way for the development of bioexploration and bioprocessing tools
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