RESUMEN
The interactive effect of metal ions namely chromium and iron has been studied under controlled conditions on the diazotropic cyanobacterium Hapalosiphon stuhlmannii and the photosynthetic green alga Scenedesmus quadricauda over the exponential growth period of the cells. The work describes by employing an exponential cell growth model, the effect of metal ions both individually and in combination, on the physiological and biochemical characteristics e.g. dry weight, chlorophylls, carotenoid and protein content of the cells over the concentration range of 0.1-3.0:0.2-16.0 microg/ml of Cr:Fe. The results reveal that the interactive effect on the dry weight, chlorophyll and protein content of both the algal cells was antagonistic at the bimetallic concentrations of 0.1:16.0, 3.0:0.2 and 3.0:16.0 microg/ml but the interaction on the protein content of both the cells was synergistic at 0.1:0.2 microg/ml of Cr:Fe. Further the degree of antagonism on dry weight was higher in H. stuhlmannii than in S. quadricauda. The degree of antagonism varied with the bimetallic concentrations and was generally lower at the higher metal concentrations. The antagonistic behavior was considered to be due to adsorption of one of the metals hindering the sorption of the other and the synergistic effect, due to adsorption of one enhancing the permeability to the other metal. The varied interactions were possibly due to the formation of metal complexes with the microalgal exudes.