Remediation of Metal Contaminated Soil by Organic Metabolites from Fungi I—Production of Organic Acids

Abstract

Investigations were made on living strains of fungi in a bioremediation process of three metal (lead) contaminated soils. Three saprotrophic fungi (Aspergillus niger, Penicillium bilaiae, and a Penicillium sp.) were exposed to poor and rich nutrient conditions (no carbon availability or 0.11 M D-glucose, respectively) and metal stress (25 µM lead or contaminated soils) for 5 days. Exudation of low molecular weight organic acids was investigated as a response to the metal and nutrient conditions. Main organic acids identified were oxalic acid (A. niger) and citric acid (P. bilaiae).

Firing Range Soils Yield a Diverse Array of Fungal Isolates Capable of Organic Acid Production and Pb Mineral Solubilization

“…Most of our environmental isolates originating from highly Pb-contaminated soils produced large quantities of mixed acids (Ն10 mM). This high level of organic acid production, as well as variable compositions of the acid mixture, has been documented in the model organisms A. niger and Penicillium bilaiae due to varying substrate C and N sources (3,36,39).…”

“…The well-characterized fungal model species A. niger has been repeatedly tested, with mixed results, for organic acid secretion, bioleaching, and remediation potential for heavy metals from various substrates, including municipal waste and fly ash (5), lowgrade mining ores (6,36), and a number of soils (3,6,39,44). A. niger is reported to produce organic acids in large quantities under specific laboratory culture conditions, with as much as 90% of the total mass of acids produced consisting of oxalic and citric acids (39).…”

“…Soil fungi have been recognized recently as potentially significant contributors to the mobilization of heavy metals by means of organic acid production in contaminated soils (2,3) and lowgrade mining ore (36) in a process often termed bioleaching. Fungal production of low-molecular-weight organic acids (LMWOAs) has been almost exclusively studied in model organisms, such as Aspergillus spp.…”

“…Fungal production of low-molecular-weight organic acids (LMWOAs) has been almost exclusively studied in model organisms, such as Aspergillus spp. (2,3,16,27,36,39,56). Despite the fact that it is a process that may contribute significantly to Pb mobilization in soils, no thorough studies of these processes in indigenous soil fungi have been reported.…”

Contaminación Ambiental Por Metales Pesados en México: Problemática Y Estrategias De Fitorremediación

“…Se ha demostrado que los ácidos orgánicos excretados por las bacterias rizosféricas también tienen efecto en la movilización de metales como el Pb, Ni, Cu, Cd y Zn (Fasim et al 2002, Arwidsson et al 2010, Li et al 2010. Esto se asume debido a la excreción de los ácidos orgánicos al suelo que ocasiona una disminución del pH (Sheng y Shia 2006), que a su vez libera los cationes metálicos al medio.…”