title: Detoxification of mercury by methanobactin from Methylosinus trichosporium OB3b.
abstract: Many methanotrophs have been shown to synthesize methanobactin, a novel biogenic copper-chelating agent or chalkophore. Methanobactin binds copper via two heterocyclic rings with associated enethiol groups. The structure of methanobactin suggests that it can bind other metals, including mercury. Here we report that methanobactin from Methylosinus trichosporium OB3b does indeed bind mercury when added as HgCl2 and, in doing so, reduced toxicity associated with Hg(II) for both Alphaproteobacteria methanotrophs, including M. trichosporium OB3b, M. trichosporium OB3b ΔmbnA (a mutant defective in methanobactin production), and Methylocystis sp. strain SB2, and a Gammaproteobacteria methanotroph, Methylomicrobium album BG8. Mercury binding by methanobactin was evident in both the presence and absence of copper, despite the fact that methanobactin had a much higher affinity for copper due to the rapid and irreversible binding of mercury by methanobactin. The formation of a gray precipitate suggested that Hg(II), after being bound by methanobactin, was reduced to Hg(0) but was not volatilized. Rather, mercury remained associated with methanobactin and was also found associated with methanotrophic biomass. It thus appears that although the mercury-methanobactin complex was cell associated, mercury was not removed from methanobactin. The amount of biomass-associated mercury in the presence of methanobactin from M. trichosporium OB3b was greatest for M. trichosporium wild-type strain OB3b and the ΔmbnA mutant and least for M. album BG8, suggesting that methanotrophs may have selective methanobactin uptake systems that may be based on TonB-dependent transporters but that such uptake systems exhibit a degree of infidelity.
authors.affiliation: Department of Civil and Environmental Engineering, The University of Michigan, Ann Arbor, Michigan, USA.
authors.forename: Alexey
authors.initials: A
authors.lastname: Vorobev
authors.forename: Sheeja
authors.initials: S
authors.lastname: Jagadevan
authors.forename: Bipin S
authors.initials: BS
authors.lastname: Baral
authors.forename: Alan A
authors.initials: AA
authors.lastname: Dispirito
authors.forename: Brittani C
authors.initials: BC
authors.lastname: Freemeier
authors.forename: Brandt H
authors.initials: BH
authors.lastname: Bergman
authors.forename: Nathan L
authors.initials: NL
authors.lastname: Bandow
authors.forename: Jeremy D
authors.initials: JD
authors.lastname: Semrau
mesh_terms: D020561:Alphaproteobacteria / Q000187:drug effects; D007093:Imidazoles / Q000378:metabolism*; D008658:Inactivation, Metabolic; D008627:Mercuric Chloride / Q000378:metabolism* / Q000633:toxicity*; D008772:Methylococcaceae / Q000187:drug effects; D042083:Methylocystaceae / Q000187:drug effects; D020602:Methylosinus trichosporium / Q000187:drug effects* / Q000378:metabolism*; D009842:Oligopeptides / Q000378:metabolism*; D010084:Oxidation-Reduction
chemical_list: D007093:Imidazoles; D009842:Oligopeptides; C491147:methanobactin; D008627:Mercuric Chloride