Energy-driven uptake of humic acids by Aspergillus niger

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Abstract
The uptake of humic acids by mycelia of Aspergillus niger was demonstrated to be energy-dependent with a sensitivity to sodium azide and to 2,4-dinitrophenol. Greatest uptake of humic acids by submerged mycelium occurred at pH 3.0 and at 32 °C. The rate of uptake was influenced by the concentration of humic acids with an apparent Km of 0.2 mg/ml and with a Vmax of 0.13 mg humic acids per gram mycelial dry weight∙10 min−1. In the absence of an added energy source, Vmax of 0.05 mg humic acids per gram mycelial dry wt∙10 min−1 was obtained; however, the affinity for humic acids by this uptake system was the same as for the energy-driven process. Apparent binding of humic acids to cell structures was indicated because only 41.8% of the humic acids taken up by the energy-dependent system could be recovered.

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