Manganese uptake and Mn(II) oxidation by the alga Scenedesmus subspicatus

Abstract:

To examine the relationships among manganese concentration in the culture medium, algae growth, manganese uptake and Mn(II) oxidation on the algal surface, we exposed the unicellular alga Scenedesmus subspicatus to a broad range of free Mn²⁺ ion concentrations. Extra- and intracellular manganese concentrations were distinguished by reducing the Mn oxides with ascorbate. A large fraction of the Mn bound by the algae occurred as reducible Mn(III/IV) oxides formed by Mn(II) oxidation, presumably on the algal surface, although these algal cells of small size are not likely to build up a large pH gradient at their surface. Limitation of growth occurred when [Mn²⁺] was lower than about 1×10^-9 M, which corresponded to an intracellular content of 10^-7 mol Mn (g algae dry weight)^-1. Inhibition of growth occurred at high [Mn²⁺], at which high concentrations of Mn (>1×10^-5 Mol Mn (g algae dry weight)^-1) were present both intracellularly and as extracellular Mn oxides. Phytoplankton collected in various lakes contained intracellular Mn and extracellular Mn oxides in similar concentrations as the Scenedesmus cultures.