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The role of mercury resistance genes...

Schaefer, Jeffra K.

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The role of mercury resistance genes in the environment and the factors controlling their expression.

Record Type:	Electronic resources : Monograph/item
Title/Author:	The role of mercury resistance genes in the environment and the factors controlling their expression./
Author:	Schaefer, Jeffra K.
Description:	200 p.
Notes:	Source: Dissertation Abstracts International, Volume: 66-01, Section: B, page: 0163.
Contained By:	Dissertation Abstracts International66-01B.
Subject:	Biogeochemistry. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3160324
ISBN:	0496938002

The role of mercury resistance genes in the environment and the factors controlling their expression.
Schaefer, Jeffra K.

The role of mercury resistance genes in the environment and the factors controlling their expression. - 200 p.

Source: Dissertation Abstracts International, Volume: 66-01, Section: B, page: 0163.

Thesis (Ph.D.)--Rutgers The State University of New Jersey - New Brunswick and University of Medicine and Dentistry of New Jersey, 2005.

Methylmercury accumulation in fish is a widespread concern due to the potential health effects in consumers. Curiously, similar concentrations of methylmercury were observed in fish from Hg contaminated and pristine environments. This "Hg accumulation paradox" can be described by an inverse relationship observed between the percent of total Hg as methylmercury (%MeHg) and the total Hg (HgT) concentration in two ecosystems of New Jersey, Berry's Creek in the Meadowlands and the Pine Barren lakes. One explanation for this phenomenon is that Hg(II) induction of mercury resistance ( mer) genes leads to increased volatilization of methylmercury in ecosystems impacted by Hg contamination. This hypothesis was supported by increased enrichment and diversity of mer genes, increased mer transcript abundance, and high rates of reductive demethylation (kdeg = 0.19 d-1) by the native microbial community in the waters of Berry's Creek (113--4220 ng/L HgT), as compared to the Pine Barren lakes (0.3--5.4 ng/L HgT) where low rates of oxidative demethylation were observed. Additionally, in the estuarine portion of Berry's Creek, a positive correlation was observed between the demethylation rate and HgT concentration, suggesting the importance of the mer inducer, Hg(II), for activity. Although methylmercury degradation in aerobic surface waters of Berry's Creek was dominated by the mer-mediated reductive pathway, a switch to oxidative demethylation (kdeg = 0.12--0.17 d-1) was observed in anoxic sediments from these same sites regardless of the high HgT concentrations (5.8--917 mug/g). Therefore, mer processes are repressed in anoxic sediments where methylmercury is produced (kmeth = 0--0.18 d-1 in Berry's Creek). Studies with the Hg-resistant denitrifier, Pseudomonas stutzeri OX, suggests that reduced intracellular Hg(II) transport may be responsible for decreased mer expression under anaerobic as compared to aerobic conditions. Although methylation processes appear to control the %MeHg in sediments, the activities mediated by the mer operon are clearly a critical factor in reducing the methylmercury concentration as it partitions into surface waters where fish live, thus decreasing the amount of methylmercury available for accumulation into food webs.

ISBN: 0496938002Subjects--Topical Terms:

545717
Biogeochemistry.

The role of mercury resistance genes in the environment and the factors controlling their expression.
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245 1 4 $a The role of mercury resistance genes in the environment and the factors controlling their expression.
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500 $a Source: Dissertation Abstracts International, Volume: 66-01, Section: B, page: 0163.
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502 $a Thesis (Ph.D.)--Rutgers The State University of New Jersey - New Brunswick and University of Medicine and Dentistry of New Jersey, 2005.
520 $a Methylmercury accumulation in fish is a widespread concern due to the potential health effects in consumers. Curiously, similar concentrations of methylmercury were observed in fish from Hg contaminated and pristine environments. This "Hg accumulation paradox" can be described by an inverse relationship observed between the percent of total Hg as methylmercury (%MeHg) and the total Hg (HgT) concentration in two ecosystems of New Jersey, Berry's Creek in the Meadowlands and the Pine Barren lakes. One explanation for this phenomenon is that Hg(II) induction of mercury resistance ( mer) genes leads to increased volatilization of methylmercury in ecosystems impacted by Hg contamination. This hypothesis was supported by increased enrichment and diversity of mer genes, increased mer transcript abundance, and high rates of reductive demethylation (kdeg = 0.19 d-1) by the native microbial community in the waters of Berry's Creek (113--4220 ng/L HgT), as compared to the Pine Barren lakes (0.3--5.4 ng/L HgT) where low rates of oxidative demethylation were observed. Additionally, in the estuarine portion of Berry's Creek, a positive correlation was observed between the demethylation rate and HgT concentration, suggesting the importance of the mer inducer, Hg(II), for activity. Although methylmercury degradation in aerobic surface waters of Berry's Creek was dominated by the mer-mediated reductive pathway, a switch to oxidative demethylation (kdeg = 0.12--0.17 d-1) was observed in anoxic sediments from these same sites regardless of the high HgT concentrations (5.8--917 mug/g). Therefore, mer processes are repressed in anoxic sediments where methylmercury is produced (kmeth = 0--0.18 d-1 in Berry's Creek). Studies with the Hg-resistant denitrifier, Pseudomonas stutzeri OX, suggests that reduced intracellular Hg(II) transport may be responsible for decreased mer expression under anaerobic as compared to aerobic conditions. Although methylation processes appear to control the %MeHg in sediments, the activities mediated by the mer operon are clearly a critical factor in reducing the methylmercury concentration as it partitions into surface waters where fish live, thus decreasing the amount of methylmercury available for accumulation into food webs.
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