Biosorption and solubilization of copper oxychloride fungicide by Aspergillus niger and the influence of calcium

Abstract

The biosorption of copper oxychloride fungicide particulates(∼1 μm diameter), at concentrations ranging from 25 to 500 ppm active ingredient (ai), by pelleted mycelium of Aspergillus niger grown on Czapek Dox medium was evaluated. The concentration of the fungicide adsorbed to the mycelium, remaining suspended or solubilized in the medium, was determined by analysis of its copper content (CuF)using atomic absorption spectrophotometry (AAS). 2-day-old pellets exhibited highbiosorption efficiency ranging from 97 ± 1.0 to 88 ± 1.2% of the initially added fungicide concentrations, respectively, within 10 min. However, underthe same conditions, amounts of the removed fungicide by 6-day-old mycelial pellets were significantly lower and ranged from 0.5 ± 0.03 to 0.15 ± 0.01%. Scanning electron microscopy studies of 2-day-old pellets supplemented with thefungicide revealed predominant aggregations of clumps and dense particulates on the hyphal tips. The adsorbed CuF of 125 ppm ai fungicide subsequently decreased from 7.5 ± 0.5 to 2.1 ± 0.1 μmol Cu (mg dry wt)^-1 after 12 h incubation. Simultaneously, the soluble portion of CuF remaining in the medium increased from 0.9 ± 0.6 to4.9 ± 0.2 μmol Cu ml^-1. The presence of 50 mM CaCl₂ resulted in a decrease of the adsorbed CuF to 3.5 ± 0.5 μmol Cu (mg dry wt)^-1 and solubilizedcopper in the medium increased to 5.9 ± 0.8 μ mol Cu ml^-1. Additionally, the cellular copper contents attained after 2 h were 0.08 ± 0.01 and 0.16 ± 0.007 μmol Cu (mg dry wt)^-1 in absence and presence of calcium, respectively. The addition of calcium to glucose-starved pellets greatly increased the medium [H⁺] which was conclusively discussed in relation to Ca²⁺/H⁺ exchangecapacity of the fungal cells. These results are of potential environmental,biotechnological and agricultural importance.