Methylation of Selenium in the Aquatic Environment

Chau, Y. K.; Wong, Pak Chung; Silverberg, B. A.; Luxon, P. L.; Bengert, G. A.

doi:10.1126/science.192.4244.1130

Cited by 188 publications

(79 citation statements)

References 12 publications

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“…The methylation activities of the freshwater samples were measured by using the modified procedure of Chau et al (4). Flasks (150 ml) containing 50-ml portions of freshwater samples, supplemented or not supplemented with nutrient broth (0.5%), glucose (0.1%), and sodium selenite or (methyl)selenocysteine (Sigma) (10 ppm), were sealed and incubated for 1 week at 25°C.…”

Section: Methodsmentioning

confidence: 99%

“…In most environments, it is also observed after addition of inorganic and organic selenium compounds, suggesting that a broadly distributed process(es) is involved (4,8,15,20,27). Bacteria have been identified as the predominant Se-methylating organisms (7,11).…”

mentioning

confidence: 99%

“…The Se-methylating bacteria have been found to mainly belong to two bacterial groups, the Proteobacteria (Enterobacter cloacae, Aeromonas sp., Pseudomonas sp., Rhodospirillum, Rhodocyclus) and the Cytophagales (Flavobacterium sp.) (4,7,9). Bacterial exposure to oxyanions (selenate [SeO 4 2Ϫ ] or selenite [SeO 3 2Ϫ ]) or organic forms of selenium (selenocystine, selenocysteine, selenomethionine) was found to generate dimethyl selenide (DMSe) and, at a lesser extent, dimethyl diselenide (DMDSe) (7,25,27).…”

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confidence: 99%

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Freshwater Bacteria Can Methylate Selenium through the Thiopurine Methyltransferase Pathway

Ranjard

Nazaret

Cournoyer

2003

Appl Environ Microbiol

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Involvement of the bacterial thiopurine methyltransferase (bTPMT) in natural selenium methylation by freshwater was investigated. A freshwater environment that had no known selenium contamination but exhibited reproducible emission of dimethyl selenide (DMSe) or dimethyl diselenide (DMDSe) when it was supplemented with an organic form of selenium [(methyl)selenocysteine] or an inorganic form of selenium (sodium selenite) was used. The distribution of the bTPMT gene (tpm) in the microflora was studied. Freshwater bacteria growing on 10 M sodium selenite and 10 M sodium selenate were isolated, and 4.5 and 10% of the strains, respectively, were shown by colony blot hybridization to hybridize with a Pseudomonas syringae tpm DNA probe. Ribotyping showed that these strains are closely related. The complete rrs sequence of one of the strains, designated Hsa.28, was obtained and analyzed. Its closest phyletic neighbor was found to be the Pseudomonas anguilliseptica rrs sequence. The Hsa.28 strain grown with sodium selenite or (methyl)selenocysteine produced significant amounts of DMSe and DMDSe. The Hsa.28 tpm gene was isolated by genomic DNA library screening and sequencing. BLASTP comparisons of the deduced Hsa.28 bTPMT sequence with P. syringae, Pseudomonas aeruginosa, Vibrio cholerae, rat, and human thiopurine methyltransferase sequences revealed that the levels of similarity were 52 to 71%. PCR-generated Escherichia coli subclones containing the Hsa.28 tpm open reading frame were constructed. E. coli cells harboring the constructs and grown with sodium selenite or (methyl)selenocysteine produced significant levels of DMSe and DMDSe, confirming that the gene plays a role in selenium methylation. The effect of strain Hsa.28 population levels on freshwater DMSe and DMDSe emission was investigated. An increase in the size of the Hsa.28 population was found to enhance significantly the emission of methyl selenides by freshwater samples supplemented with sodium selenite or (methyl)selenocysteine. These data suggest that bTPMT can play a role in natural freshwater selenium methylation processes.

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Freshwater Bacteria Can Methylate Selenium through the Thiopurine Methyltransferase Pathway

Ranjard

Nazaret

Cournoyer

2003

Appl Environ Microbiol

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“…Inorganic and organic Se compounds undergo microbial transformations in fresh water sediments mainly to dimethylselenide (47), such transformations being a factor in the metalloid's cycling. At present, it is not possible to assess the specific impact of acidification on Se biotransformations.…”

Section: Selenium and Acidity In Aquatic Ecosystemsmentioning

confidence: 99%

Potential impact of acid precipitation on arsenic and selenium.

Mushak¹

1985

Environ Health Perspect

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The potential impact of acidic precipitation on the environmental mobility of the metalloids arsenic (As) and selenium (Se) has not been given much attention and is poorly understood. As with other elements, the interest here is the potential effect of environmental acidification on environmental behavior in ways that are relevant to human exposure to these metalloids. Available information on acid precipitation and the environmental behavior of these metalloids do, however, permit some preliminary conclusions to be drawn.Both As and Se appear to be mobilized from household plumbing into tap water by the corrosive action of soft, mildly acidic water, while surface water catchment systems in areas impacted by acidic deposition may contain elevated soluble As levels.Acidification of aquatic ecosystems that are drinking water sources may pose the prospect of enhanced release of As from sediment to water as well as reduction in water levels of Se. Acidification of ground waters, where As appears to be especially mobile, is of particular concern in this regard.The potential impact of acidic deposition on As and Se in soils cannot readily be assessed with respect to human exposure, but it would appear that the behavior of these metalloids in poorly buffered, poorly immobilizing soils, e.g., sandy soils of low metal hydrous oxide content, would be most affected. The effect is opposite for the two elements; lowered pH would appear to enhance As mobility and to reduce Se availability.Altered acidity of both soil and aquatic systems poses a risk for altered biotransformation processes involving both As and Se, thereby affecting the relative amounts of different chemical forms varying in their toxicity to humans as well as influencing biogeochemical cycling.

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“…Biomethylation of sulphur (S) occurs in marine and terrestrial environments, and contributes significantly to the global biogeochemical S cycle (mostly via dimethyl sulphide (DMS)) 11 . Due to chemical similarities between Se and S, it has been postulated that the elements have similar biomethylation pathways 12,13 . Similarly to Se, arsenic (As) is a trace element irregularly distributed in soils and groundwater, and elevated levels of inorganic As in groundwater in Southeast Asia, for example, have resulted in serious human health problems 14 .…”

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confidence: 99%

Natural wetland emissions of methylated trace elements

et al. 2014

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Natural wetlands are well known for their significant methane emissions. However, trace element emissions via biomethylation and subsequent volatilization from pristine wetlands are virtually unstudied, even though wetlands constitute large reservoirs for trace elements. Here we show that the average volatile fluxes of selenium (o0.12 mg m À 2 day À 1 ), sulphur (o37 mg m À 2 day À 1 ) and arsenic (o0.54 mg m À 2 day À 1 ) from a pristine peatland are considerable and consistent over two summers. We compare these fluxes with the total concentrations in the peat and show that selenium is up to 40 times more efficiently volatilized than arsenic, and over 100 times more efficiently volatilized than sulphur. We further show that the volatilization of selenium and arsenic increases with temperature, implying that emissions of these health-relevant trace elements will increase with global warming. We suggest that biomethylation and volatilization in wetlands play a crucial role in the mobilization and global biogeochemical cycling of trace elements.

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Methylation of Selenium in the Aquatic Environment

Cited by 188 publications

References 12 publications

Freshwater Bacteria Can Methylate Selenium through the Thiopurine Methyltransferase Pathway

Freshwater Bacteria Can Methylate Selenium through the Thiopurine Methyltransferase Pathway

Potential impact of acid precipitation on arsenic and selenium.

Natural wetland emissions of methylated trace elements

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