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

Abstract

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 Ϯ 92 pg cm Ϫ2 h Ϫ1 ) compared to the dark (114 Ϯ 70 pg cm Ϫ2 h Ϫ1 ), 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 M 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 M 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 ␤-keto acids) and a component of DOM leads to the production of volatile polybromomethanes.Bromoform (CHBr 3 ) is an important source of tropospheric organobromine that can penetrate into the stratosphere in chemically significant amounts, in spite of its relatively short atmospheric lifetime (Sturges et al. 2000). Over the past decade, marine algal production of bromoform and other polyhalomethanes have been repeatedly demonstrated and it has been estimated that marine algae produce approximately 70% of global bromoform (Carpenter and Liss 2000).Bromoperoxidase (BrPO) has been identified as the brominating enzyme. Its activity requires H 2 O 2 , bromide ion, and a suitable organic substrate. Theiler et al. (1978) proposed a mechanism for polybromomethane biosynthesis that involved the bromination by BrPO of ␤-keto acids (e.g., 3-oxooctanoic acid) and cyclic ␤-diketones that are found in marine algae. Bromination produces an intermediate brominated heptanone that yields CH 2 Br 2 , CHBr 3 , and 1-pentyl bromide on hydrolysis. Wever et al. (1991) proposed that CHBr 3 is produced in situ from components of DOM (dissolved organic matter) that are brominated by a reaction with hypobromous acid (HOBr), which itself is a product of BrPO activity.In vivo bromination of phenol red by Ascophyllum nodusum was shown to be enhanced in the presence of exogenous H 2 O 2 (Wever et al. 1991). Similarly, bromoform (CHBr 3 ) production was enhanced with the addition of H 2 O 2 1 C...

Gaseous emissions from flooded rice paddy agriculture

“…It would be unlikely that 1‐butene is not photochemically produced, but these results suggest that future studies of 1‐butene production from terrestrial plants may be worthwhile. Bromoform is known to be emitted from several macroalgea [ Carpenter and Liss , 2000; Manley and Barbero , 2001] although emissions by terrestrial plants have not yet been observed. Seasonally integrated bromoform emissions in planted chambers (0.025 ± 0.013 mg m −2 ) were higher than those from control chambers (0.014 mg m −2 ), but not significantly so.…”

CHBr3, CH2Br2, and CHClBr2in U.S. coastal waters during the Gulf of Mexico and East Coast Carbon cruise

“…Current evidence suggests that marine CHBr 3 , CH 2 Br 2 , and CHClBr 2 are primarily produced naturally, such as by macroalgae, ice algae and phytoplankton [e.g., Carpenter and Liss , 2000; Gschwend and MacFarlane , 1986; Manley and Barbero , 2001; Manley et al , 1992; Moore et al , 1996; Sturges et al , 1992, 1993; Tokarczyk and Moore , 1994]. CHBr 3 and CHClBr 2 also have anthropogenic sources as by‐products of water disinfection [e.g., Nieuwenhuijsen et al , 2000; Quack and Wallace , 2003; Ram et al , 1990].…”

BIOGEOCHEMICAL CYCLES | Iodine

“…Whether the evolved volatile iodine species produced by marine algae have a biological function is currently unknown. They may simply be a by-product of the intra-and intercellular removal of the H 2 O 2 from algal tissue (Manley and Barbero, 2001), alternatively they may also act to deter the grazing of zooplankton. These biological phenomena have, however, significant impacts on atmospheric chemistry on scales from the local and global (see Section Reactive Iodine Species in the Atmosphere).…”