Effect of Montmorillonite and Trace Elements on the Growth of Penicillium frequentans: I. Ammonium Nitrogen Source

In laboratory studies, the addition of clay to culture media has been shown to increase microbial growth and metabolic activity. The objective of this study was to determine the influence of montmorillonite clay and three trace element treatments on the growth of Penicillium frequentans with NH₄-N as the N source. The fungus was grown in 100 ml of a defined basal medium with glucose as the carbon-energy source and NH₄Cl as the N source. The trace element treatments were (i) no trace elements, (ii) trace-element solution 1 which contained the following final concentration of trace elements (µg/ml): FeSO₄·7H₂O, 0.20; ZnSO₄·7H₂O, 5.0; CuSO₄·5H₂O, 0.02; CoSO₄·7H₂O, 0.02; Na₂MoO₄·2H₂O, 0.02; and H₃BO₃, 0.10; and (iii) trace element solution 2 which contained a 0.1M pH 6.0 phosphate buffer plus the following final concentration of trace elements (µg/ml): Fe₂(SO₄)₃·nH₂O, 10.0; ZnSO₄·7H₂O, 2.5; CuSO₄·5H₂O, 0.5; CoCl₂·6H₂O, 1.5; Na₂MoO₄·2H₂O, 2.5; H₃BO₃, 0.5; MnSO₄·H₂O, 1.0; and CaCl₂, 10.0. Either clay, at a concentration of approximately 500 mg/100 ml, or distilled water (controls) was added in dialysis tubing to the trace-element treatments. In the no trace element treatment, the biomass of the control was increased from 624 to 1,211 mg with the addition of clay. In the trace-element solution 1, biomass was increased from 1,084 to 1,197 mg with the addition of clay. In both treatments, the addition of clay increased CO₂ evolution, glucose and N utilization, and the economic coefficient of cell synthesis. Neither biomass nor metabolic activity was increased in the trace element-solution 2 with clay addition. There were no significant differences in biomass production among the no trace element treatment with clay, the trace-element solution 1 with clay, and the trace-element solution 2 with or without clay. Except for the trace-element solution 2, which contained a phosphate buffer, the addition of clay resulted in a decrease in the pH of the medium. In all three treatments, the addition of clay increased the Cu and Fe content of the fungus. With the addition of clay, the Zn content of the fungus increased in all treatments except the trace element solution 1. After fungal growth, the structural Zn and Cu contents of the clay, in the no trace-element treatment, were reduced from 51 to 21 µg/g and 37 to 21 µg/g, respectively. It appeared that P. frequentans removed trace elements from the clay for growth which accounted for a large portion of the stimulation in growth due to clay.