Physiological constraints on bromoform (CHBr₃) production by Ulva lactuca (Chlorophyta)

Physiological factors affecting bromoform (CHBr 3 ) production by Ulva lactuca were investigated using metabolic inhibitors and presumed substrates of bromoperoxidase (BrPO). The metabolic inhibitors were used at a verified physiologically active concentration. Bromoform production was nearly tripled in the light (376 ± 92 pg cm −2 h −1 ) compared to the dark (114 ± 70 pg cm −2 h −1 ), was inhibited in the light in the presence of the photosynthetic inhibitor DCMU, and was inhibited in the dark in the presence of mitochondrial respiratory inhibitor rotenone. Removal of H 2 O 2 from seawater (treatment with catalase) decreased CHBr 3 production in the light and dark. Addition of H 2 O 2 to incubations at either 1.0 mM or 100 µM significantly decreased CHBr 3 production in the light and inhibited photosynthesis. In the dark, CHBr 3 production was decreased and respiration inhibited in the presence of 1 mM H 2 O 2 ; CHBr 3 production was enhanced and respiration was not affected in the presence of 100 µM H 2 O 2 . Removal of dissolved organic matter (DOM) from seawater decreased CHBr 3 production, as did the addition of alternative BrPO substrates. These results suggest the presence of an extracellular and intracellular BrPO that protects the alga from both internally produced and externally present H 2 O 2 . The results show that H 2 O 2 produced as a result of photosynthetic and respiratory electron transport, presumably by superoxide dismutase, is available to BrPO for bromination, and that the bromination of an unidentified metabolite (presumably Βߚketo acids) and a component of DOM leads to the production of volatile polybromomethanes.