title: Enhanced availability of mercury bound to dissolved organic matter for methylation in marine sediments.
abstract: The forms of inorganic mercury (HgII) taken up and methylated by bacteria in sediments still remain largely unknown. From pure cultures studies, it has been suggested that dissolved organic matter (DOM) may facilitate the uptake either by acting as a shuttle molecule, transporting the HgIIatom to divalent metal transporters, or by binding HgIIand then being transported into the cell as a carbon source. Enhanced availability of Hg complexed to DOM has however not yet been demonstrated in natural systems. Here, we show that HgIIcomplexed with DOM of marine origin was up to 2.7 times more available for methylation in sediments than HgIIadded as a dissolved inorganic complex (HgII(aq)). We argue that the DOM used to complex HgIIdirectly facilitated the bacterial uptake of HgIIwhereas the inorganic dissolved HgII-complex adsorbed to the sediment matrix before forming bioavailable dissolved HgIIcomplexes. We further demonstrate that differences in net methylation in sediments with high and low organic carbon content may be explained by differences in the availability of carbon to stimulate the activity of Hg methylating bacteria rather than, as previously proposed, be due to differences in HgIIbinding capacities between sediments.
authors.affiliation: Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT 06340, USA; Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA.
authors.forename: Nashaat M
authors.initials: NM
authors.lastname: Mazrui
authors.affiliation: Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT 06340, USA; Center for Environment and Sustainability, University of Gothenburg, Box 170, SE-405 30,Gothenburg, Sweden.
authors.forename: Sofi
authors.initials: S
authors.lastname: Jonsson
authors.affiliation: Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA.
authors.forename: Sravan
authors.initials: S
authors.lastname: Thota
authors.affiliation: Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton CT 06340, USA; Department of Chemistry, University of Connecticut, 55 North Eagleville Road, Storrs CT 06269, USA.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Mason