EFFECT OF NICKEL ON CERTAIN PHYSIOLOGICAL AND BIOCHEMICAL BEHAVIORS OF AN ACID-TOLERANT CHLORELLA-VULGARIS

This study concerns the inhibitory effects of acid pH and nickel on gr owth, nutrient (NO3- and NH4+) uptake, carbon fixation, O-2 evolution, electron transport chain and enzyme (nitrate reductase and ATPase) ac tivities of acid tolerant and wild-type strains of Chlorella vulgaris. Though a general reduction in all these variables was noticed with de creasing pH, the tolerant strain was found to be metabolically more ac tive than the wild-type. A reduced cation (NH4+, Na+, K+ and Ca2+) upt ake, coupled with a facilitated influx of anions (NH4+, PO43- and HCO3 -), suggested the development of a positive membrane potential in acid tolerant Chlorella. Nevertheless, a tremendous increase in ATPase act ivity at decreasing pH revealed the involvement of superactive ATPase in exporting H+ ions and keeping the internal pH neutral. A difference in Na+ and K+ efflux of the two strains at decreasing pH suggests the re is a difference in membrane permeability. The low toxicity of Ni in the acid tolerant strain may be due to the low Ni uptake brought abou t by a change in membrane potential as well as in permeability. Hence, the development of superactive ATPase and a change in both membrane p otential and permeability not only offers protection against acidity, but also co-tolerance to metals.