Binding of manganese by Antarctic Phaeocystis pouchetii and the role of bacteria in its release

The growth of Antarctic Phaeocystis pouchetii and associated bacteria in culture, and the binding and release of manganese were investigated using cultures derived from three clonal isolates collected from Prydz Bay, Antarctica, in November and December 1982. The cultured strains accumulated manganese from the culture medium. The concentration of Mn²⁺ in the alga was up to 58 times that of the medium. The Mn²⁺ apparently binds to the mucilage secreted by the cells and gives the alga its characteristic brown colour. Oxidation or complexing of Mn²⁺ by P. pouchetii was also indicated. Bacterial growth on the mucilage is inhibited in rapidly growing cultures by acrylic acid produced in the mucilage. Once the growth of P. pouchetii and production of ccrylic acid slow, bacterial numbers increase, leading to the solubilization of the mucilage and the release of Mn²⁺. In cool-temperate, subpolar and polar seas where P. pouchetii may form dense blooms, the binding and subsequent release of manganese may have important consequences for competing phytoplankton.