SORPTION OF HEAVY-METALS TO THE FILAMENTOUS BACTERIUM THIOTHRIX STRAIN A1

A study was undertaken to determine the ability of the filamentous bac terium Thiothrix strain Al to sorb heavy metals from solution. Cells o f Thiothrix strain Al were harvested, washed, and suspended in solutio ns of metals. After an equilibration period, biomass was separated fro m solution and the metal content in acid-digested cells and/or filtrat es was determined by atomic absorption spectrophotometry. Sorption of nickel and zinc was very rapid; most of the sorbed metal was bound in less than 10 min. The sorption data for copper fit the Freundlich isot herm, and nickel and zinc data fit biphasic Freundlich isotherms. Sorp tion of both nickel and zinc was dependent on cell age. Cells harveste d 24 h after inoculation sorbed approximately one-half of the amount o f metal per gram cell protein than did cells harvested after 48, 72, o r 96 h. Calcium and magnesium effectively competed with zinc for bindi ng sites, whereas potassium had only a slight effect on the capacity o f cells to sorb zinc. The primary mechanism of metal sorption apparent ly was ion exchange, because 66 to 75% of nickel or zinc could be deso rbed by placing metal-laden cells in a solution of 5 mM CaCl2. A compe tition experiment with nickel and zinc indicated that both metals occu pied the same sorption sites. The strong chelating agents EDTA and NTA effectively prevented metal uptake, but lactate enhanced the uptake o f nickel. Thiothrix strain Al grown in nickel-containing medium had a relatively low uptake of nickel compared with uptake by resting cells suspended in a simple buffer solution.