BROMINATING ACTIVITY OF THE SEAWEED ASCOPHYLLUM-NODOSUM - IMPACT ON THE BIOSPHERE

Macroalgae are an important source of volatile halogenated organic compounds, such as bromoform and dibromomethane. The mechanism by which these compounds are formed is still elusive. We report that the brown seaweeds Laminaria saccharina, Laminaria digitata, Fucus vesiculosis, Pelvetia canaliculata, and Ascophyllum nodosum and the red seaweeds Chondrus crispus and Plocamium hamatum contain bromoperoxidases. The intact plants are able to brominate exogeneous organic compounds when H2O2 and Br- are added to seawater. Further, we show that the brominating activity of the brown macroalga A. nodosum, which contains a vanadium bromoperoxidase located on the thallus surface, occurs when the plant is exposed to light and not in the dark. The rate of bromination of exogenous organic compounds in seawater by this plant is 68 nmol (g of wet alga)-1 h-1. HOBr is a strong biocidal agent and we propose that the formation of HOBr by this seaweed is part of a host defense system.