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This paper investigates Aspergillus niger's behaviour in the presence of mobile Al 3+ species by evaluating the changes in oxalate exudation at various aluminium contents. When the fungus was exposed to Al 3+ , no significant changes in oxalate production were observed until 100 mg.L -1 aluminium was reached resulting in oxalate production decrease by 18.2%. By stripping the culture medium completely of phosphate, even more prominent decrease by 34.8% and 67.1% at 10 and 100 mg.L -1 aluminium was observed, respectively, indicating the phosphate's significance instead of Al 3+ in oxalate production. Our results suggest that the low phosphate bioavailability, which most likely resulted from its interaction with Al 3+ , stimulated the overproduction of oxalate by A. niger. Furthermore, when the fungus was incubated in aluminium-free media supplemented with 0.1 mM of phosphate, oxalate production increased up to 281.5 μmol.g -1 , while at 1.85 mM of available phosphate only 80.7 μmol.g -1 of oxalate was produced. This indicates that oxalic acid is produced by fungus not as a mean to detoxify aluminium, but as an attempt to gain access to additional phosphate., Competing Interests: Declaration of competing interest The author declare that they have no known competing financial interest or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2019. Published by Elsevier Inc.)

This paper provides a unique comparison of the performance of four wild-type Aspergillus niger strains in remediation of aluminium(III)-contaminated aqueous solutions. The direct fungal aluminium removal via biosorption and bioaccumulation was compared among all fungal strains, including bioaccumulation efficiency during dynamic and static cultivation. Our results indicate that aluminium bioaccumulation by living biomass outperformed biosorption, although biosorption by non-living biomass is a less time-demanding process. Among others, only one strain significantly differed regarding comparison of dynamic and static bioaccumulation. In this case, a significantly higher removal performance was achieved under dynamic cultivation conditions at initial aluminium(III) concentrations over 2.5 mg L -1 . Although the fungal sensitivity towards aluminium(III) differed among selected fungal strains, there was no apparent correlation between the strains' removal performance and their adaptive mechanisms.

This contribution investigates aluminium mobilization from main aluminium pools in soils, phyllosilicates and oxyhydroxides, by acidic and chelating exometabolites of common soil fungi Aspergillus niger and A. clavatus. Their exometabolites' acidity as well as their ability to extract aluminium from solid mineral phases differed significantly during incubation. While both strains are able to mobilize aluminium from boehmite and aluminium oxide mixture to some extent, A. clavatus struggles to mobilize any aluminium from gibbsite. Furthermore, passive and active fungal uptake of aluminium enhances its mobilization from boehmite, especially in later growth phase, with strong linear correlation between aluminium bioaccumulated fraction and increasing culture medium pH. We also provide data on concentrations of oxalate, citrate and gluconate which are synthesized by A. niger and contribute to aluminium mobilization. Compared to boehmite-free treatment, fungus reduces oxalate production significantly in boehmite presence to restrict aluminium extraction efficiency. However, in presence of high phyllosilicates' dosages, aluminium is released to an extent that acetate and citrate is overproduced by fungus. Our results also highlight fungal capability to significantly enhance iron and silicon mobility as these elements are extracted from mineral lattice of phyllosilicates by fungal exometabolites alongside aluminium., (Copyright © 2017 Elsevier Inc. All rights reserved.)

This contribution investigates the efficient and environmentally friendly aluminium leaching from red mud (bauxite residue) by 17 species of filamentous fungi. Bioleaching experiments were examined in batch cultures with the red mud in static, 7-day cultivation. The most efficient fungal strains in aluminium bioleaching were Penicillium crustosum G-140 and Aspergillus niger G-10. The A. niger G-10 strain was capable to extract up to approximately 141 mg·L(-1) of aluminium from 0.2 g dry weight red mud. Chemical leaching with organic acids mixture, prepared according to A. niger G-10 strain's respective fungal excretion during cultivation, proved that organic acids significantly contribute to aluminium solubilization from red mud., (Copyright © 2015 Elsevier Inc. All rights reserved.)

Bioleaching of aluminium mineral boehmite by filamentous fungus Aspergillus niger was compared to chemical leaching by citric, oxalic and hydrochloric acids to evaluate the significance of A. niger’s metabolites on aluminium mobilization from this natural component of the aluminium ore. Our results highlighted that leaching efficiency of hydrochloric acid at pH 2 was 2.7 times lower compared to fungal bioleaching efficiency. When the organic acids were compared, oxalic acid was a stronger aluminium leaching agent than citric acid. The results suggest that fungal metabolites significantly promoted the release of aluminium and that their acidic properties, despite being useful, were not the most critical factor in the bioleaching of aluminium. [ABSTRACT FROM AUTHOR]

Presence of microorganisms in soils strongly affects mobility of metals. This fact is often excluded when mobile metal fraction in soil is studied using extraction procedures. Thus, the first objective of this paper was to evaluate strain Aspergillus niger ’s exometabolites contribution on aluminium mobilization. Fungal exudates collected in various time intervals during cultivation were analyzed and used for two-step bio-assisted extraction of alumina and gibbsite. Oxalic, citric and gluconic acids were identified in collected culture media with concentrations up to 68.4, 2.0 and 16.5 mmol L −1 , respectively. These exometabolites proved to be the most efficient agents in mobile aluminium fraction extraction with aluminium extraction efficiency reaching almost 2.2%. However, fungal cultivation is time demanding process. Therefore, the second objective was to simplify acquisition of equally efficient extracting agent by chemically mimicking composition of main organic acid components of fungal exudates. This was successfully achieved with organic acids mixture prepared according to medium composition collected on the 12th day of Aspergillus niger cultivation. This mixture extracted similar amounts of aluminium from alumina compared to culture medium. The aluminium extraction efficiency from gibbsite by organic acids mixture was lesser than 0.09% which is most likely because of more rigid mineral structure of gibbsite compared to alumina. The prepared organic acid mixture was then successfully applied for aluminium extraction from soil samples and compared to standard single step extraction techniques. This showed there is at least 2.9 times higher content of mobile aluminium fraction in soils than it was previously considered, if contribution of microbial metabolites is considered in extraction procedures. Thus, our contribution highlights the significance of fungal metabolites in aluminium extraction from environmental samples, but it also simplifies the extraction procedure inspired by bio-assisted extraction of aluminium by common soil fungus A. niger . [ABSTRACT FROM AUTHOR]

Abstract: Nanometer-sized titanium dioxide was used as a solid-phase extractant for the separation and preconcentration of trace amounts of Al(III) prior to its determination by electrothermal atomic absorption spectrometry (ET AAS) and inductively coupled plasma optical emission spectrometry (ICP OES). The optimal conditions for the proposed solid phase extraction (SPE; 50mg TiO2, 10min extraction time, pH 6.0, HCl and HNO3 as eluents) and ET AAS measurement (1500°C pyrolysis and 2600°C atomization temperatures, Mg(NO3)2 as matrix modifier) were obtained. The adsorption capacity of TiO2 was 4.1mg Al g−1 TiO2. Two modes of the proposed procedure were compared, (I) batch and elution mode with the elution of Al from TiO2 phase by nitric or hydrochloric acid, and (II) batch and slurry mode (without elution) with the direct TiO2 phase-slurry sampling. Finally, the batch and slurry mode of nanometer-sized TiO2 SPE with slurry ET AAS detection and quantification was preferred and used for the determination of trace amounts of total dissolved cationic Al species in synthetic and natural water samples. The method accuracy was checked by the analysis of lake water CRM TMDA-61 and by the technique of analyte addition (sample spiking). Under the optimal conditions, the calibration curve for batch and slurry TiO2 SPE with a 10-fold preconcentration was linear up to 40μg L−1 Al. The limit of detection (LOD) and the limit of quantification (LOQ) was 0.11μg L−1 Al and 0.35μg L−1 Al, respectively, with a preconcentration factor of 20 and a relative standard deviation (RSD) lower than 5%. [Copyright &y& Elsevier]

Abstract: An optimized BCR three-step sequential extraction procedure, several single extractions and the reactive aluminium determination after chelating ion-exchange on Iontosorb Salicyl were used for the fractionation of Al in soil samples from a mining area with sulphidic deposits. The aluminium amounts released by used extraction procedures were valuated and discussed. The new indicative values of fractional Al concentrations in five Chinese certified reference materials (GBW 07103, 07304, 07401, 07405, 07407) were determined after Al fractionation by optimized BCR three-step sequential extraction procedure. The aluminium toxicity indexes calculated for two different soil extracts and plant samples were used for assessment of Al toxicity to plants. It can be concluded that the most sensitive indicator of increasing aluminium toxicity to plants is determination of reactive Al species in soil solution by chelating ion-exchange solid phase extraction. The atomic absorption spectrometry with nitrous oxide-acetylene flame was used for determination of total Al amounts and the Al concentration in different extraction fractions as well. [Copyright &y& Elsevier]

Abstract: The aim of the presented work is to evaluate the selectivity of the operationally defined procedures for the aluminium fractionation in the reference materials and the environmental samples affected by the mining activity. The combination of the sequential optimized BCR (European Commission Community Bureau of Reference) three-step, the single (H2O, CaCl2, Na2S2O4, NH4F, (NH4)2C2O4, HCl, NTA, EDTA, DTPA) and the solid phase chelating ion-exchange extraction procedures was performed for the aluminium fractionation in the samples. The amount of the reactive Al determined by the solid phase extraction on the chelating resin Iontosorb Salicyl is the most important operationally defined fraction of aluminium from the aspect of its negative effects on the environment. The available Al concentrations obtained from the different operationally defined fractionation methods were compared. The flame atomic absorption spectrometry was used for the aluminium quantification. The X-ray diffraction analyse of the samples was performed for the mineral composition determination. The precision, the repeatability and the accuracy for the all steps of the optimized BCR sequential extraction procedure were checked on six reference materials (SRM 2710, RSS SO-2, RSS SO-4, CRM SA-B, SRM RTH 912, CRM 025-050). The precision and the repeatability were very good with the R.S.D. values ≤11%. The fraction specific accuracy was excellent. The new indicative fractional Al values in the used reference materials are published. [Copyright &y& Elsevier]