The Production of Oxalate by Aspergillus niger under Different Lead Concentrations

Abstract

In this study, using a typical acid-producing fungi, Aspergillus niger (A. niger, CGMCC 23272), we investigated the capacity of organic acid production under different lead (Pb) concentrations. A. niger has a high Pb tolerance, which can maintain the growth of hypha at 1500 mg/L Pb concentration. Oxalic acid is the primary organic acid produced by A. niger. A. niger was shown to maintain the ability to produce oxalic acid under different Pb concentrations, which ranged from 522.8 to 1130.5 mg/L. The formed lead oxalate also confirmed the production of oxalic acid by A. niger. Meanwhile, the formation of lead oxalate minerals dominated the resistance of Pb toxicity by A. niger. More than 95% of Pb cations were removed by A. niger under different Pb concentrations. The high Pb toxicity (1500 mg/L) could stimulate pyruvate dehydrogenase enzyme activities, which increased from 0.05 to 0.13 nmol/min/g after three days of incubation. The low Pb toxicity (500 and 1000 mg/L) could improve the production of oxalic acid by A. niger. This indicates that the metabolism of organic acid by A. niger can be improved by a high Pb concentration via the tricarboxylic acid cycle.