title: The Use of a Mercury Biosensor to Evaluate the Bioavailability of Mercury-Thiol Complexes and Mechanisms of Mercury Uptake in Bacteria.
abstract: As mercury (Hg) biosensors are sensitive to only intracellular Hg, they are useful in the investigation of Hg uptake mechanisms and the effects of speciation on Hg bioavailability to microbes. In this study, bacterial biosensors were used to evaluate the roles that several transporters such as the glutathione, cystine/cysteine, and Mer transporters play in the uptake of Hg from Hg-thiol complexes by comparing uptake rates in strains with functioning transport systems to strains where these transporters had been knocked out by deletion of key genes. The Hg uptake into the biosensors was quantified based on the intracellular conversion of inorganic mercury (Hg(II)) to elemental mercury (Hg(0)) by the enzyme MerA. It was found that uptake of Hg from Hg-cysteine (Hg(CYS)2) and Hg-glutathione (Hg(GSH)2) complexes occurred at the same rate as that of inorganic complexes of Hg(II) into Escherichia coli strains with and without intact Mer transport systems. However, higher rates of Hg uptake were observed in the strain with a functioning Mer transport system. These results demonstrate that thiol-bound Hg is bioavailable to E. coli and that this bioavailability is higher in Hg-resistant bacteria with a complete Mer system than in non-resistant strains. No difference in the uptake rate of Hg from Hg(GSH)2 was observed in E. coli strains with or without functioning glutathione transport systems. There was also no difference in uptake rates between a wildtype Bacillus subtilis strain with a functioning cystine/cysteine transport system, and a mutant strain where this transport system had been knocked out. These results cast doubt on the viability of the hypothesis that the entire Hg-thiol complex is taken up into the cell by a thiol transporter. It is more likely that the Hg in the Hg-thiol complex is transferred to a transport protein on the cell membrane and is subsequently internalized.
authors.affiliation: Department of Environmental Sciences, Rutgers University, New Brunswick, New Jersey, United States of America.
authors.forename: Udonna
authors.initials: U
authors.lastname: Ndu
authors.affiliation: Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey, United States of America.
authors.forename: Tamar
authors.initials: T
authors.lastname: Barkay
authors.affiliation: Department of Marine Sciences, University of Connecticut, Groton, Connecticut, United States of America.
authors.forename: Robert P
authors.initials: RP
authors.lastname: Mason
authors.affiliation: Department of Environmental Health, Harvard School of Public Health, Boston, Massachusetts, United States of America.
authors.forename: Amina
authors.initials: A
authors.lastname: Traore Schartup
authors.affiliation: Marine Chemistry Department, King Abdul-Aziz University, Jeddah, Saudi Arabia.
authors.forename: Radwan
authors.initials: R
authors.lastname: Al-Farawati
authors.affiliation: Department of Biochemistry and Microbiology, Rutgers University, New Brunswick, New Jersey, United States of America.
authors.forename: Jie
authors.initials: J
authors.lastname: Liu
authors.affiliation: Department of Environmental Sciences, Rutgers University, New Brunswick, New Jersey, United States of America.
authors.forename: John R
authors.initials: JR
authors.lastname: Reinfelder
mesh_terms: D001412:Bacillus subtilis / Q000378:metabolism*; D001682:Biological Availability; D001692:Biological Transport; D015374:Biosensing Techniques; D003553:Cystine / Q000378:metabolism; D004926:Escherichia coli / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D008628:Mercury / Q000737:chemistry* / Q000378:metabolism*; D013438:Sulfhydryl Compounds / Q000737:chemistry*
chemical_list: D013438:Sulfhydryl Compounds; D003553:Cystine; D008628:Mercury; D005978:Glutathione