Lead mineral transformation by fungi

Abstract

Pyromorphite (Pb5(PO4)3Cl), the most stable lead mineral under a wide range of geochemical conditions [1], can form in urban and industrially contaminated soils [2] [3] [4] [5]. It has been suggested that the low solubility of this mineral could reduce the bioavailability of lead, and several studies have advocated pyromorphite formation as a remediation technique for lead-contaminated land [3] [5] [6], if necessary using addition of phosphate [6]. Many microorganisms can, however, make insoluble soil phosphate bioavailable [7] [8] [9] [10], and the solubilisation of insoluble metal phosphates by free-living and symbiotic fungi has been reported [11] [12] [13] [14] [15]. If pyromorphite can be solubilised by microbial phosphate-solubilising mechanisms, the question arises of what would happen to the released lead. We have now clearly demonstrated that pyromorphite can be solubilised by organic-acid-producing fungi, for example Aspergillus niger, and that plants grown with pyromorphite as sole phosphorus source take up both phosphorus and lead. We have also discovered the production of lead oxalate dihydrate by A. niger during pyromorphite transformation, which is the first recorded biogenic formation of this mineral. These mechanisms of lead solubilisation, or its immobilisation as a novel lead oxalate, have significant implications for metal mobility and transfer to other environmental compartments and organisms. The importance of considering microbial processes when developing remediation techniques for toxic metals in soils is therefore emphasised.

Microbial Relatives of the Seed Storage Proteins of Higher Plants: Conservation of Structure and Diversification of Function during Evolution of the Cupin Superfamily

“…It has also been exploited in the solubilization of heavy metals from bauxite, clay, sand, sewage sludge, and other metal bearing materials. In many of these applications, Aspergillus niger is favored as the best species for oxalic acid production (251,252,279), in contrast to the medical dangers of such production by this organism.…”

Fungal Bioweathering of Mimetite and a General Geomycological Model for Lead Apatite Mineral Biotransformations

“…1; Table 1). The bioleaching of other lead apatites, such as pyromorphite and vanadinite, by A. niger and other organic acid-producing fungi with the simultaneous bioprecipitation of lead oxalate has been described in the literature (39,44,45). This suggests the existence of a common pattern in fungal bioleaching of the main lead apatites Fig.…”

“…This work examined the stability of natural mimetite [Pb 5 (AsO 4 ) 3 Cl] in the presence of the ubiquitous soil fungus Aspergillus niger, which possesses well-known geoactive properties (1,2,39,40,(44)(45)(46)(47)(48)(49)(50)(51)(52)(53), including citric, gluconic, and oxalic acid production (51,54,55). Experiments clearly revealed the complete bioweathering of a pure natural mimetite by the fungus and the simultaneous bioprecipitation of pure lead oxalate [Pb(C 2 O 4 )] as a new mycogenic biomineral ( Fig.…”

“…The organism used for the bioleaching tests was Aspergillus niger van Tieghem (ATCC 201373), from the culture collection of the Geomicrobiology Group (University of Dundee). A. niger was chosen because it has been shown to have significant geoactive properties in mineral bioweathering of the lead apatites pyromorphite and vanadinite (1,2,39,40,(44)(45)(46)(47)(48)(49)(50)(51)(52)(53). Moreover, this fungus is a common soil saprotroph and can produce substantial amounts of organic acids, e.g., oxalic, citric, and gluconic acids (51,54,55 15.…”

An Acidophilic Bacterial-Archaeal-Fungal Ecosystem Linked to Formation of Ferruginous Crusts and Stalactites

“…In addition to prokaryotes, fungi were also shown to be involved in the dissolution of inorganic materials, which is mostly explained by their morphological and physiological flexibility and also by their ability to create various symbiotic relationships (Sayer et al 1999;Ehrlich, 2006;Gadd et al 2007;Gadd, 2007;Gadd, 2008;Gadd, 2010). Even in the harshest environments, fungi are fundamental components of all rock types.…”