Nickel uptake and release in nickel-resistant and - sensitive strains of Scenedesmus acutus f. alternans (Chlorophyceae)

Abstract Intracellular uptake and extracellular adsorption of Ni 2+ were compared in three Niresistant (B4, Cu-Tol, and Ni-Tol) and one Ni-sensitive (UTEX 72) strains of Scenedesmus acutus f. alternans , to assess the role of these processes in Ni-resistance. Intracellular uptake was highest in the most sensitive strain (UTEX 72) during a 24 h exposure to 50 fmol Ni 2+ per cell (equivalent to 50 μM). However, B4 could grow longer and accumulated substantially more Ni 2+ than UTEX 72 after a 3 days exposure period, suggesting that B4 is a Ni-accumulator. Ni 2+ transport rate in Cu-Tol and Ni-Tol was only about 1 3 that in UTEX 72, indicating that Ni-Tol and Cu-Tol exclude Ni 2+ . A positive linear relationship was found between intracellular uptake and extracellular adsorption and Ni 2+ dosage in all four strains in the range of 2–500 fmol Ni 2+ per cell. Although extracellular adsorption as percentage of total uptake was lowest in UTEX 72 in most cases studied, all four strains bound substantial amounts of Ni 2+ to their cell surface, suggesting that extracellular binding contributes only slightly to Ni-resistance in these strains. That low temperature and darkness strongly inhibited but did not abolish Ni 2+ uptake in all four strains suggests that active transport was the major means of Ni 2+ uptake, but that passive Ni 2+ transport also existed. All four strains released more Ni 2+ in dark than under light after 28 h of resuspension in Ni-free medium, suggesting that Ni 2+ release is a passive process which is counteracted by active Ni 2+ uptake in the light. Ni-resistance in these strains can not be attributed to active Ni 2+ release.