Bromoperoxidase and iodoperoxidase enzymes and production of halogenated methanes in marine diatom cultures

Abstract

Halogenated methanes produced in the oceans are important as carriers of chlorine, bromine, and iodine into the atmosphere. There they play roles in the regulation of ozone in the stratosphere and perhaps in the Arctic troposphere at polar sunrise. While the mechanisms for the production of some polyhalogenated compounds by marine macrophytes have previously been substantially elucidated, the same has not been true in the case of marine phytoplankton. We describe laboratory experiments on the production of various brominated and iodinated compounds in cultures of marine diatoms, obtained from the Provasoli‐Guillard Center for Culture of Marine Phytoplankton collections (Bigelow Laboratory for Ocean Sciences, Maine, USA; CCMP). Species examined included Nitzschia sp. (CCMP 580), Nitzschia arctica, Porosira glacialis, and two Navicula sp. (CCMP 545 and 546). A suite of brominated compounds, notably bromoform and dibromomethane, is produced by the Nitzschia and Porosira species. Nitzschia sp.(CCMP 580) was grown in sufficient quantities to allow the identification of a bromoperoxidase enzyme, which is assumed to be responsible not only for the CHBr3 and CH2Br2 production but also for CH2I2 which was measured in those cultures. Chloroiodomethane was produced, either directly by the algae or by a photochemical reaction of CH2I2. One Navicula species (CCMP 545), found to produce CH2I2 and CH2ClI, was shown to possess an iodoperoxidase. Bromoform and dibromomethane were not detected in cultures of this species. Other compounds produced in certain of these non axenic cultures included methyl and ethyl iodide, and bromoiodomethane.

Changing concentrations of CO, CH 4 , C 5 H 8 , CH 3 Br, CH 3 I, and dimethyl sulfide during the Southern Ocean Iron Enrichment Experiments

“…1E) and CH 3 Cl remained unchanged. Methyl halides are known to be produced in seawater by marine microorganisms (32)(33)(34)(35). Some methyl halides are known to be chemically removed from seawater by nucleophilic attack (36), hydrolysis (37), and bacteria (38)(39)(40).…”

Halocarbons associated with Arctic sea ice

“…Concentrations of all other halocarbons are higher in sea ice brine and in ice covered waters, consistent with production by ice diatoms [e.g. Moore et al 1996] or by other ice processes such as the concentration effect or abiotic reactions . Table 2.…”

“…Previous work monitoring production of halocarbons over the life cycle of diatoms has shown that production is greatest during growth, and less during stationary and dying phases [Moore et al 1996], which explains a lower halocarbon ratio between the ice brine and dense algae mats than the cell density ratio. When halocarbon concentrations in the different sample types collected at the ice station are compared (Figure 9), the potential for some halocarbons to be enhanced in sea ice brine is clear, though the range is large and overlaps with the seawater concentrations.…”

“…Diatoms are known to live in sea ice brine channels [Garrison & Buck 1989], and the production of halocarbons by diatoms is well established [Sturges et al 1992, Tokarczyk & Moore 1994, via enzymes active in the metabolism of the cell [Manley 2002, Moore et al 1996.…”

Alternatives to Methyl Bromide: A Florida Perspective.

“…While methyl bromide is abundant in the atmosphere, soil fumigation is just one source of the material. Other sources include, emissions from leaded gasoline (113) and biomass burning (6), as well as natural sources such as oceans (80), salt marshes (102), rice paddies (101) and litter decomposition. It is estimated that approximately 30% of methyl bromide emissions result from soil fumigation (126).…”