Effect of Inorganic and Organic Ligands on the Bioavailability of Methylmercury as Determined by Using a mer-lux Bioreporter

Abstract

A mer-lux bioreporter was constructed to assess the bioavailability of methylmercury [CH 3 Hg(II)] in Escherichia coli. The bioreporter was shown to be sensitive, with a detection limit of 2.5 nM CH 3 Hg(II), and was used to investigate the effects of chlorides, humic acids, and thiols on the bioavailability of CH 3 Hg(II) in E. coli. It was found that increasing the concentration of chlorides resulted in an increase in CH 3 Hg(II) bioavailability, suggesting that there was passive diffusion of the neutral complex (CH 3 HgCl 0 ). Humic acids were found to reduce the bioavailability of CH 3 Hg(II) in varying degrees. Complexation with cysteine resulted in increased bioavailability of CH 3 Hg(II), while assays with equivalent concentrations of methionine and leucine had little or no effect on bioavailability. The mechanism of uptake of the mercurial-cysteine complexes is likely not passive diffusion but could result from the activities of a cysteine transport system. The bioavailability of CH 3 Hg(II) decreased with increasing glutathione concentrations.

Diffusive gradients in thin films for predicting methylmercury bioavailability in freshwaters after photodegradation

“…A similar phenomenon happens also when working with living organisms. Some authors stated that an increase in DOM concentration led to a decrease in MeHg bioavailability, as tested in algae, seston and hydropsychids, or bacteria (Gorski et al, 2008;Tsui and Finlay, 2011;Luengen et al, 2012;Ndu et al, 2012) as the MeHg-DOM complexes are too large or hydrophilic to pass through the cell membrane.…”

Recent advances in the study of mercury methylation in aquatic systems

“…This "bioreporter" has been successful in showing enhanced uptake of inorganic mercury when newly deposited (Chiasson-Gould et al 2014), under low base cation concentrations (Daguené et al 2012), and at lower pH (Kelly et al 2003). The same bioreporter has been used to assess the bioavailability of MeHg, showing that increasing chloride concentration resulted in increased MeHg uptake; the presence of both humic acids and cysteine reduced MeHg bioavailability (Ndu et al 2012). This approach has also been used to show that dissolved organic carbon both mobilizes inorganic Hg and alters cell walls to facilitate uptake (Chiasson-Gould et al 2014).…”

“…For one, the bioreporter must be constructed, which can be time consuming. For example, it took Ndu et al (2012) 20 cycles before the lux reporter proteins were synthesized by the bacterium of interest. In addition, significant care must be taken to ensure that the growth medium is not contaminated with low levels of Hg that will promote light production.…”

Differentiated availability of geochemical mercury pools controls methylmercury levels in estuarine sediment and biota

“…In addition to factors controlling MeHg formation, concentration of MeHg in biota is influenced by factors regulating the entry of MeHg into the food web and its trophic transfer. Irrespective of whether the cellular uptake mechanisms involve dissolved MeHg complexes in surrounding water or in the gut, the uptake is governed by the chemical speciation of dissolved MeHg and to a large extent limited by sorption to particles or complexation with dissolved organic ligands, which are not bioavailable [15][16][17] . Yet our understanding of processes controlling the availability of different geochemical MeHg pools, and the quantitative importance of such processes at the ecosystem level, remains insufficient.…”