Abstract
The effect of Cd2+ and a combination of Cd2+ with non-inhibiting levels of metals like Ca2+, Zn2+ and Hg2+ on the uptake of ammonia and phosphate by Anacystis nidulans IU625 (ATCC 27144) was investigated. Increasing concentrations of Cd2+ resulted in the subsequent inhibition of both NH4+ and PO43- uptake. The uptake kinetics was studied by monitoring short-term uptake rates at varying substrate levels. The values for Vmax (maximum uptake capacity) and Km (half saturation constant) were obtained using the double reciprocal plot. The NH4+ uptake as such, was found to be more sensitive to the heavy metal than the PO43- uptake as fairly low levels of Cd2+ were sufficient to inhibit the process significantly. However, the uptake kinetics for both NH4+ and PO43- was altered if Cd2+ was present in combination with other divalent cations such as Ca2+, Zn2+ and Hg2+. Zn2+ acted antagonistically to Cd2+ toxicity. Similarly, the Ca2+-Cd2+ combination protected against inhibition by Cd2+ ions. Hg2+ behaved differently: the Cd2+-Hg2+ combination resulted in increased inhibition.
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