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.