Release of reactive bromine and iodine from diatoms and its possible role in halogen transfer in polar and tropical oceans

Abstract

An in situ incubation assay measuring the bromination and iodination of phenol red was developed to detect the release of reactive bromine and iodine (primarily hypobromous acid [HOBr] and hypoiodous acid [HOI], respectively) from a putative extracellular bromoperoxidase of marine diatoms. Six of 11 species showed significant release compared to controls. Polar species were particularly active, releasing 0.6-180 fmol HOBr cell 21 h 21 (0.04-1.8 mmol HOBr [mg total chlorophyll] 21 h 21 ; at the seawater bromide concentration, 840 mmol L 21 ) and 1.9-271 fmol HOI cell 21 h 21 (0.02-2.7 mmol HOI [mg total chlorophyll] 21 h 21 , at 100 mmol L 21 iodide). Porosira glacialis consistently showed the highest rates of release. Several temperate diatoms, including Achnanthes cf longipes, known to have a bromide-sensitive peroxidase involved in stalk formation, and warmwater species also showed the ability to release reactive bromine and iodine. This release was influenced by light, temperature, bromide (and iodide) concentration, H 2 O 2 concentration, and pH. The rate of HOBr release by polar diatoms was much greater than bromoform emissions measured by others from laboratory cultures and seaice algae in the field. This indicates that most of the HOBr released may react with dissolved organic matter (DOM) to form nonvolatile bromine organics. Some fraction of diatom-produced HOBr and HOI may also form volatile Br 2 and I 2 , which could transfer to the polar troposphere. The reaction of diatom-released reactive bromine and iodine with seawater DOM may represent the major mechanism in the formation of oceanic polybromo-and polyiodo-methanes.

Transformation of iodate to iodide in marine phytoplankton driven by cell senescence

“…However, upon re-supply of nitrate, iodide production stopped and the concentration declined while cells resumed exponential growth. Thus, an iodide oxidation mechanism must have been active during this time that oxidised 80 nmol l -1 iodide over 25 d. Diatoms have been observed previously to oxidise iodide to iodate (Sugawara & Terada 1967), and other phytoplankton have been shown to possess iodoperoxidases (Murphy et al 2000, Hill & Manley 2009, though these enzymes are normally not capable of oxidising iodide to iodate. A review of the literature on this subject reveals only one reference to a chloroperoxidase in the fungus Caldariomyces fumago that can oxidise iodide to iodate (Thomas & Hager 1968).…”

Characterization of Iodine-Related Molecular Processes in the Marine Microalga Tisochrysis lutea (Haptophyta)

“…In Laminaria digitata, the haloperoxidases play a key role in the specific uptake of iodide from seawater and nucleotide sequences encoding for vanadium iodoperoxidases were reported (Colin et al, 2005;Leblanc et al, 2006;Verhaeghe et al, 2008). In microalgae, some studies reported haloperoxidase activity (Moore et al, 1996;Murphy et al, 2000;Hill and Manley, 2009;Hughes and Sun, 2016), however, putative genes encoding putative iodoperoxidases have not been identified to date. Moreover, iodotyrosine deiodinases were only described in metazoan and bacteria (Phatarphekar et al, 2014;Taylor and Heyland, 2017) and iodothyronine deiodinases were restricted to metazoa and between social amoebae (Lobanov et al, 2007;Orozco et al, 2012;Singh et al, 2014).…”

Distribution, transport, and production of volatile halocarbons in the upper waters of the ice‐covered high Arctic Ocean

“…It has then been shown that production of halocarbons by the macroalgae Ulva Lactuca in light decreased with >80% when DOM was removed from the incubation seawater [Manley and Barbero, 2001], which supports such a mechanism. More recently, it has also been shown that species of diatoms release HOBr and IOBr, which may react with extracellular DOM [Hill and Manley, 2009]. Although most widespread in eukaryotic organisms, bromoperoxidases, although generally with lower halogenating activity, have also been identified in bacteria, e.g., in Pseudomonas aureofaciens [Van Pée and Lingens, 1985], and it has been shown that cyanobacteria may produce halocarbons [Johnson et al, 2011;Karlsson et al, 2008;Schall et al, 1996].…”