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Biosynthesis of gold nanoparticles (GNPs) using fungal extracellular filtrate as the source of reducing and capping agent is reported here. The study includes the fabrication of GNPs using a soil fungus CO1 in a very effective way for material synthesis. Morphological, molecular, and phylogenetic studies of the fungus CO1 show that it is similar to the Aspergillus austwickii. Aspergillus austwickii CO1 is reported for the first time for GNPs synthesis in this paper. The characteristic surface plasmon resonance (SPR) peak for colloidal GNPs was observed at 532 nm. The GNPs remained stable for about 90 days at room temperature. The optimum temperature, pH, and substrate concentration were 100 °C, pH 9, and 1 mM AuCl4− concentration, respectively, to obtain maximum possible stability and monodispersity of synthesized GNPs. The GNPs were characterized using instrumental analysis. Transmission electron microscopy analysis confirmed the formation of spherical particles of size 14.7 ± 6.9 nm. The kinetics of the GNPs synthesis reaction was investigated by measuring particle size and zeta potential as a function of time. The stability of biosynthesized GNPs was better than chemically synthesized citrate-GNPs (Cit-GNPs) when exposed to high ionic concentration by the addition of sodium chloride in the GNP solution. The biosynthesized GNPs were able to resist aggregation even with the addition of 0.2 mM of NaCl, while Cit-GNPs aggregated at much lower concentration of 0.05 mM NaCl. Selective reactivity of the GNPs was observed toward Mg2+ ions, with a minimum detection limit of 40 ppm. Detection could be visualized by naked eye also. Thus, the non-toxic biosynthesized GNPs could further assist in the Mg2+ optical sensing application of water. [ABSTRACT FROM AUTHOR]

Tungsten is an important alloying component for the production of different materials. Its efficient extraction from different sustainable resources is necessary to meet the growing demand in the future. In this context, an attempt has been made to recover it from a goldmine overburden sample using the fungal bioleaching technique. The sample contains 0.023% of WO3 in the form of scheelite. The prospect of bioleaching for tungsten recovery from the sample was evaluated by varying pulp density from 1 to 7% (w/v). The leaching rate of tungsten decreased with the increase of pulp density. The maximum tungsten recovery of 86.8% (w/w) could be achieved at the condition of pulp density, 1% (w/v); pH, 6.8; temperature, 32 °C; speed, 120 rpm; contact time, 10 days. Growth of the fungal strain Aspergillus niger in terms of organic acids production was evaluated during the bioleaching experiment and found to be maximum at the pulp density of 1% (w/v). The leaching kinetics of tungsten followed the chemical control model. [ABSTRACT FROM AUTHOR]

The present work deals with the use of iron/sulfur-oxidizing bacterium Acidithiobacillus ferrooxidans for the desulfurization of a coal sample from Assam, India. The coal sample contains 3.87% w/w of organic sulfur, 1.4% w/w pyritic sulfur, and 1.29% w/w of sulfate sulfur which altogether are contributing to its total sulfur content of 6.56% w/w. The microbial process followed the oxidative-desulfurization mechanism for the removal of sulfur from the coal sample. The bacterium performed cleavage of the sulfide bonds in pyrite to release the inorganic sulfur. Mass spectroscopic analysis revealed that the bacterial strain A. ferrooxidans performed oxidative desulfurization of a model sulfur-containing organic compound dibenzothiophene to 2-hydroxy biphenyl through the formation of dioxy-dibenzothiophene. A. ferrooxidans cells played the catalytic role to release the sulfur present in organic and inorganic form in the coal sample. The microbial desulfurization process conducted in a shake flask scale (500 mL) removed about 79% of total sulfur from the coal sample in 14 days. [ABSTRACT FROM AUTHOR]

Mineralogically distinct coal samples respond differently to microbial attack. In the present study, a mixed meso-acidophilic bacterial consortium predominantly comprising of Acidithiobacillus ferrooxidans strain was investigated for its biodesulphurization abilities for three distinct sulphur bearing samples (Goa CPC, Rajasthan Lignite, Assam Coal) of Indian origin in iron (9K+) and iron-free (9K−) media. A media devoid of Fe (II) iron was more effective for sulphur removal with maximum desulphurization of 45.19% for Assam coal followed by 36.8% for Rajasthan Lignite and 23.38% for CPC respectively. The proximate analysis, FTIR patterns and XRD analysis of the samples provided better insights into understanding the mineralogical and compositional changes in the coal matrix. Owing to the higher efficiency, Assam coal was additionally subjected to further optimization studies and characterization of the treated coal through TGA. The study indicated that the gross calorific values for all the samples increased following microbial treatment in 9K− media thereby providing a scope for further scale-up studies. [ABSTRACT FROM AUTHOR]

Since the sulfur specific cleavage is vital for the organic sulfur removal from fossil fuel, we explored potential bacterial strains of MTCC (Microbial Type Culture Collection) to desulfurize the Dibenzothiophene (DBT) through C-S bond cleavage (4-S pathway). MTCC strains Rhodococcus rhodochrous (3552), Arthrobacter sulfureus (3332), Gordonia rubropertincta (289), and Rhodococcus erythropolis (3951) capable of growing in 0.5 mM DBT were examined for their desulfurization ability. The presence of dsz genes as well as the metabolites was screened by polymerase chain reaction (PCR) and HPLC, respectively. All these strains showed > 99% DBT desulfurization with 10 days of incubation in minimal salt medium. From the HPLC analysis it was further revealed that these MTCC strains show differences in the end metabolites and desulfurize DBT differently following a variation in the regular 4-S pathway. These findings are also well corroborating with their respective organization of dszABC operons and their relative abundance. The above MTCC strains are capable of desulfurizing DBT efficiently and hence can be explored for biodesulfurization of petrochemicals and coal with an eco-friendly and energy economical process. [ABSTRACT FROM AUTHOR]

In the current era, the alarming rate at which coal is being burned as a fuel is causing concern with regard to the release of sulphur oxides. According to reports, global coal consumption has increased by 0.4% in 2014. While countries like UK, Ukraine etc. have witnessed a decline in coal consumption, some others like India, China, Africa and North America have increased their use of coal to meet the energy requirements of the growing human population. The increasing use of coal has led to extensive investigations for finding an ecofriendly clean coal technology. Dibenzothiophene (DBT) and some of its alkylated derivatives present in the form of organic sulphur in coal have received a great deal of attention in the past few years because of their recalcitrant nature. Considering the economic and environmental prospects, biodesulphurization is being regarded as an effective tool for the degradation of DBT, with concomitant application towards sulphur removal from coal. Owing to the importance of microbial applications towards production of clean coal, the present review discusses some of the recent findings in the area of DBT biodegradation. In addition, current advances in coal biodesulphurization are reviewed, concluding with a consideration of future prospects for the rapidly growing energy sector. [ABSTRACT FROM AUTHOR]

Biosynthesis of monodispersed nanoparticles, along with determination of potential responsible biomolecules, is the major bottleneck in the area of bionanotechnology research. The present study focuses on an ecofriendly, ambient temperature protocol for size controlled synthesis of gold nanoparticles, using the fungus Aspergillus terreus IF0. Gold nanoparticles were formed immediately, with the addition of chloroauric acid to the aqueous fungal extract. Synthesized nanoparticles were characterized by UV-Vis spectroscopy, TEM-EDX, and XRD analysis. Particle diameter and dispersity of nanoparticles were controlled by varying the pH of the fungal extract. At pH 10, the average size of the synthesized particles was in the range of 10-19 nm. Dialysis to obtain high and lowmolecular weight fraction followed by FTIR analysis revealed that biomolecules larger than 12 kDa and having -CH, - NH, and -SH functional groups were responsible for bioreduction and stabilization. In addition, the synthesized gold nanoparticles were found to be selectively bactericidal against the pathogenic gram negative bacteria, Escherichia coli. [ABSTRACT FROM AUTHOR]

Study of six different freshwater microalgae, collected from Odisha, eastern region of India, has been carried out to find out their potential for biodiesel production. The growth, total lipid, and fatty acid composition of six microalgal strains were determined. Chlorella sp. IMMTCC-2, which exhibited high lipid content with considerable amount of unsaturated fatty acids, was selected for culture in a self-designed photobioreactor in order to study the scale-up possibilities. The result shows significant increase in lipid accumulation from logarithmic phase to stationary phase in the photobioreactor, i.e., from 12.4 to 28.3%. Analyses of the present results suggest that Chlorella sp. IMMTCC-2 is appropriate for biodiesel production. [ABSTRACT FROM AUTHOR]

A bacterial strain isolated from a contaminated soil degraded phenol as the sole source of carbon and energy. It was identified as Serratia plymuthica with the help of its biochemical, physiological and morphological characteristics. The bacterium was able to tolerate and degrade phenol up to a concentration of 1050mgl−1. High concentration of phenol in minimal medium had inhibitory effect on bacteria. The bacterium was able to degrade other aromatic compounds like benzoic acid, ortho-, meta-, para-cresol, protocatechuate, catechol and tryptophan. Phenol was degraded through ortho-pathway. Crude cell extract showed presence of ring cleavage enzyme catechol 1,2-dioxygenase. Specific activity of catechol 1,2-dioxygenase was 0.134μmolemin−1 mg−1 protein. Effect of phenol as inhibitory substrate show that higher the concentration of phenol in the medium more is the negative effect on growth of bacteria and subsequent biodegradation. This bacterium grew well in pH range of 5 to 9 and temperature range of 30 to 40°C. Presence of other carbon source like glucose in the phenol minimal medium affects negatively the rate of degradation of phenol but increases the specific growth rate of the bacteria. [Copyright &y& Elsevier]

A native isolate, 9C, identified as Rhodococcus ruber (Genbank Accession number – KY029073) was studied for dibenzothiophene degradation and subsequent bio-desulphurization of three different sulphur bearing materials (NE coal containing organic sulphur; lignite containing pyritic sulphur and a calcined petroleum-coke) of Indian origin. The isolate could degrade 0.25 mM DBT through the 4S pathway within 7 days. Preliminary studies for sulphur removal using the 9C isolate indicated NE coal to be more amenable (29% sulphur removal) followed by Lignite (15.87%) and CPC (14.83%) respectively. Characterization through XRD and FTIR along with the proximate and ultimate analysis of all the samples provided more insights into the changes in calorific values as well as the chemical constitution of the samples following microbial treatment. Owing to the amenability of NE coal, the effect of time, size fraction and pulp density were optimized. The best bio-desulphurization conditions for NE coal indicated 36% total sulphur removal (organic–53%, pyritic–18% and sulphate sulphur–14% respectively). Analytical characterization studies confirmed that the energy value of the NE coal was not affected due to biodesulphurization, rather it contributed towards an increase in gross calorific value from 6698 cal/g to 6812 cal/g following microbial treatment. [ABSTRACT FROM AUTHOR]

Two ore samples, one obtained from a partially leached heap with suspended operations for about four years and the other through sonic drilling of a discarded dump were tested for the amenability/feasibility of copper extraction through reactor and column leaching. Mineralogical analysis of the samples indicated the dominant sulphide minerals to be chalcopyrite and pyrite. Various process parameters such as the effect of acid concentration, time, oxidant, pulverization and temperature were studied for the reactor leaching experiments. A maximum of 91% Cu extraction can be achieved while leaching the pulverized sonic drilled sample at 90 °C for 3 h. On the other hand, column leaching studies at 1 kg scale showed 65–70% Cu extraction with an acid concentration of 2.7% ( v / v ) for both the samples. Sequential leaching of the chemically leached residues of both sonic drilled and heap leached pad sample yielded additional 13.2% and 22.2% Cu, respectively in 20 days of bacterial leaching using a mixed culture of meso-acidophilic bacterial consortium. Column leaching studies showed that the heap leached pad sample was more amenable to leaching than the sonic drilled one. Further, during the downstream processing of the leach liquors, the solvent extraction efficiency was about 95% and the Cu metal deposited by electrowinning was of 99.9% purity. A tentative process flowsheet for the recovery of copper was also prepared. [ABSTRACT FROM AUTHOR]

The nickeliferous chromite overburden (COB) awaits a suitable technology to extract the obstinate nickel ingrained in its goethite matrix. In the present study, a novel Bio-Reduction Acid Leaching (BRAL) approach has been proposed using dissimilatory iron reducing bacteria (DIRB) which is inherently capable of transforming iron mineral phases via bio-reduction (BR). Mineralogical characterization of the bio-reduced COB using XRD and FTIR confirmed the phase transformation of goethite to hematite and magnetite with exposure of the nickel oxide peaks. Further, morphological characterization using FESEM vividly highlighted the changes of acicular goethite to granular magnetite deposits on the extra polymeric substance (a scaffold for electron transfer) secreted by DIRB consortium over the surface of COB. Further, enhanced nickel extraction was achieved with a reductive acid leaching (AL) approach with 6N sulfuric acid and 2% glucose (reducing agent) at 65 °C for 6 h. A cumulative of 83.6% nickel was achieved through this BRAL approach. The pregnant leach solution (PLS) generated as a result of the AL approach was subjected to a hydrometallurgical route to recover metallic nickel. Solvent extraction (SX) of the PLS was performed using 0.5 M NaD2EHPA as extractant. The pregnant nickel-loaded electrolyte was subjected to electrowinning (EW) to recover metallic nickel of 99.6% purity. The process flow-sheet is believed to provide a suitable eco-friendly, potential method to efficiently extract nickel from low grade nickel laterites to meet the ever growing demands caused by depletion of high grade nickel sulfidic ores. [ABSTRACT FROM AUTHOR]

Dumping of low-grade chalcopyrite encompasses several environmental problems. Despite slow dissolution rate, meso-acidophilic bioleaching is preferred for the extraction of copper from such ores. In the present study, meso-acidophilic bioleaching of a low-grade chalcopyrite in the presence of an acid-processed waste newspaper (PWp) is discussed for the first time. The study illustrated a strong catalytic response of PWp with enhanced bio-recovery of copper from acid-conditioned chalcopyrite. A maximum of 99.13% copper recovery (0.36% Cu dissolution/day) was obtained in 6 days of bioleaching in the presence of 2 gL − 1 PWp in contrast to only 5.7% copper in its absence. FTIR analysis of bioleached residues revealed similar spectral patterns to the original acid-conditioned ore in the presence of PWp, thus indicating less development of passivation layer which was also confirmed through a complementary Raman characterization of the bioleached residues. Further, a reaction mechanism (chemistry) was proposed suggesting the possible role of PWp as the electron donor under oxygen limiting conditions which facilitated microbial reduction of Fe (III). The resulting biochemical changes provided an energy source for the bacteria, thus allowing free flow of electrons through the ore surface, thus contributing towards enhanced bioleaching of copper. [ABSTRACT FROM AUTHOR]

The most adverse outcome of increasing industrialization is contamination of the ecosystem with heavy metals. Toxic heavy metals possess a deleterious effect on all forms of biota; however, they affect the microbial system directly. These heavy metals form complexes with the microbial system by forming covalent and ionic bonds and affecting them at the cellular level and biochemical and molecular levels, ultimately leading to mutation affecting the microbial population. Microbes, in turn, have developed efficient resistance mechanisms to cope with metal toxicity. This review focuses on the vital tolerance mechanisms employed by the fungus to resist the toxicity caused by heavy metals. The tolerance mechanisms have been basically categorized into biosorption, bioaccumulation, biotransformation, and efflux of metal ions. The mechanisms of tolerance to some toxic metals as copper, arsenic, zinc, cadmium, and nickel have been discussed. The article summarizes and provides a detailed illustration of the tolerance means with specific examples in each case. Exposure of metals to fungal cells leads to a response that may lead to the formation of metal nanoparticles to overcome the toxicity by immobilization in less toxic forms. Therefore, fungal-mediated green synthesis of metal nanoparticles, their mechanism of synthesis, and applications have also been discussed. An understanding of how fungus resists metal toxicity can provide insights into the development of adaption techniques and methodologies for detoxification and removal of metals from the environment. • Review focuses on mechanisms used by fungus to resist the toxicity by heavy metals. • Mechanisms:biosorption, bioaccumulation, biotransformation, and efflux of metal ions. • Interaction with toxic metals-copper, arsenic, zinc, cadmium, nickel is discussed. • Exposure of metals to fungal cells leads formation of metal nanoparticles. • Fungal-mediated metal nanoparticles synthesis-mechanism-applications discussed. [ABSTRACT FROM AUTHOR]

Bionanotechnology has revolutionized nanomaterial synthesis by providing a green synthetic platform using biological systems. Among such biological systems, microalgae have tremendous potential to take up metal ions and produce nanoparticles by a detoxification process. The present study explores the intracellular and extracellular biogenic syntheses of silver nanoparticles (SNPs) using the unicellular green microalga Scenedesmus sp. Biosynthesized SNPs were characterized by AAS, UV-Vis spectroscopy, TEM, XRD, FTIR, DLS, and TGA studies and finally checked for antibacterial activity. Intracellular nanoparticle biosynthesis was initiated by a high rate of Ag(+) ion accumulation in the microalgal biomass and subsequent formation of spherical crystalline SNPs (average size, 15-20 nm) due to the biochemical reduction of Ag(+) ions. The synthesized nanoparticles were intracellular, as confirmed by the UV-Vis spectra of the outside medium. Furthermore, extracellular synthesis using boiled extract showed the formation of well scattered, highly stable, spherical SNPs with an average size of 5-10 nm. The size and morphology of the nanoparticles were confirmed by TEM. The crystalline nature of the SNPs was evident from the diffraction peaks of XRD and bright circular ring pattern of SAED. FTIR and UV-Vis spectra showed that biomolecules, proteins and peptides, are mainly responsible for the formation and stabilization of SNPs. Furthermore, the synthesized nanoparticles exhibited high antimicrobial activity against pathogenic gram-negative and gram-positive bacteria. Use of such a microalgal system provides a simple, cost-effective alternative template for the biosynthesis of nanomaterials in a large-scale system that could be of great use in biomedical applications.