title: Chemical mimicking of bio-assisted aluminium extraction by Aspergillus niger's exometabolites.
abstract: 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.
authors.affiliation: Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkovičova 6, Bratislava 842 15, Slovakia.
authors.forename: Katarína
authors.initials: K
authors.lastname: Boriová
authors.affiliation: Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkovičova 6, Bratislava 842 15, Slovakia. Electronic address: urik@fns.uniba.sk.
authors.forename: Martin
authors.initials: M
authors.lastname: Urík
authors.affiliation: Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkovičova 6, Bratislava 842 15, Slovakia.
authors.forename: Marek
authors.initials: M
authors.lastname: Bujdoš
authors.affiliation: Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkovičova 6, Bratislava 842 15, Slovakia.
authors.forename: Ivana
authors.initials: I
authors.lastname: Pifková
authors.affiliation: Faculty of Natural Sciences, Comenius University, Mlynská dolina, Ilkovičova 6, Bratislava 842 15, Slovakia.
authors.forename: Peter
authors.initials: P
authors.lastname: Matúš
mesh_terms: D000144:Acids, Acyclic / Q000378:metabolism*; D000535:Aluminum / Q000378:metabolism; D000536:Aluminum Hydroxide / Q000378:metabolism*; D000537:Aluminum Oxide / Q000378:metabolism*; D001234:Aspergillus niger / Q000378:metabolism*; D019343:Citric Acid; D008903:Minerals / Q000378:metabolism; D012987:Soil
chemical_list: D000144:Acids, Acyclic; D008903:Minerals; D012987:Soil; D019343:Citric Acid; D000536:Aluminum Hydroxide; D000535:Aluminum; D000537:Aluminum Oxide
keywords: Aluminium; Extraction; Fungal metabolites; Mobility; Organic acids